SUBCOURSE EDITIONOD1747 A

REFRIGERATION ANDAIR CONDITIONING I

REFRIGERATION AND AIR CONDITIONING I(Fundamentals)

Subcourse OD1747

Edition A

United States Army Combined Arms Support CommandFort Lee, VA 23801-1809

10 Credit Hours

INTRODUCTION

This subcourse is the first of four subcourses devoted to basic instruction in refrigeration and air conditioning.

This subcourse explains the fundamentals of electricity and their application in the refrigeration process. Itdiscusses circuits, motors, and troubleshooting. This is followed by a discussion of fundamentals and the maintenance ofthe gasoline engine. The theory of refrigeration is also explained based on the characteristics of refrigerants.

Unless otherwise stated, whenever the masculine gender is used, both men and women are included.

INTRODUCTION

WITHIN THE LAST 20 years refrigeration has become a vital part of American economy. Not only does nearly everyhousehold have its own private machine for the manufacture of ice and cold, but the vast industry of transporting, storing,and selling fresh foods would collapse overnight without the facilities to preserve fruits, meats, and vegetables. Furthermore,many amazing therapies of medical science depend upon refrigeration.

All over the world the Army maintains bases equipped with the latest war materiel for keeping the peace or fordefending our country. The men who man these bases must have suitable working conditions, proper food, and the besthospital treatment possible. In accomplishing these tasks, the Army makes use of every phase of refrigeration.Consequently, it must have men who will make a career of installing and maintaining the many refrigeration units it owns.

This course is offered to personnel who wish to improve their knowledge of the science of refrigeration. Thismemorandum explains the fundamental reactions which make up the process of present-day refrigeration. It should helpthe man who is interested in increasing his knowledge of refrigeration. Review exercises are at the end of each chapter.

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ACKNOWLEDGMENT

Grateful acknowledgement is made to Allied Chemical Corporation; E. I. du PontNemours and Company, Inc., and the American Society of Heating, Refrigeration, andAir Conditioning Engineers for permission to use illustrations from their publications.

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CONTENTS

Page

Introduction......................................................................................................................................................................i

Acknowledgement...........................................................................................................................................................ii

Chapter

1 Principles of Electricity....................................................................................................................................................1

2 Fundamentals of Gasoline Engines...............................................................................................................................41

3 Physics of Refrigeration.................................................................................................................................................48

4 Refrigerants....................................................................................................................................................................58

Glossary.........................................................................................................................................................................63

Appendix........................................................................................................................................................................66

Answer to Review Exercises.........................................................................................................................................77

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CHAPTER 1

Principles of Electricity

We all use electrical equipment, such a lights, radio,television, electric stove and heaters, refrigerators, airconditioners and many more. We use these items manytimes a day and accept them as a matter of course. Aslong as the electrical equipment operates properly, weaccept it with little concern about what actually takesplace. Each of these devices operates because electriccurrent flows through it.

2. To understand how electricity functions, you needto know the theory of electricity. The word "electric" isderived from the Greek word meaning "amber." Theancient Greeks used the word describe the strange forceof attraction and repulsion that was exhibited by amberafter it had been rubbed with a cloth. By knowing whatelectricity does, people have long ago developed theorieswhich now are proving productive.

3. After centuries of experimentation by the world’sgreatest scientists, laws by which electricity operates arebecoming more widely known and better understood.Also, the world has arrived at a generally accepted theoryof the composition of matter. Therefore you must learnabout “matter” and certain magnetic effects exhibited bymatter.

1. Electrical Fundamentals

1-1. Matter means all substance - solids, liquids, andgases. Today, the accepted theory is that matter iscomposed of three long-lived particles and many moreshort-lived particle. We are concerned only with one ofthe three long-lived particles - the electrons.

1-2. Electron Flow. Where there is a generalmovement of electrons in one direction, an electriccurrent flows. The electrons together with protons(positively charged particles) and neutrons (neutralparticles), make up atoms, of which all substances arecomposed. The protons and neutrons are in the nucleus(center of atom) and generally do not move about withina substance. The remainder of the atom is composed of

electrons, which are in constant motion about thenucleus.

1-3. Electrons move at a high rate of speed in orbitaround the nucleus and carry a negative charge. Theelectrons apparently do not bunch up as the protons do inthe nucleus. An atom may be compared to our planetarysystem, with the sun as the nucleus and the earth andother planets representing the electrons. This isillustrated in figure 1, which shows the similarity betweena hydrogen atom and our earth-sun system. Morecomplex atoms have a larger nucleus and additionalelectrons. The electrons are considered to be relativelyloose and are usually considered to be that which makeup an electric current or flow.

1-4. Electricity is often referred to as static electricityor dynamic electricity. A generator is said to producedynamic electricity, and from this comes the word“dynamo” as another name for a generator. This is amachine which converts mechanical energy to electricalenergy. Generally speaking, we are able to controldynamic electricity so that it is a useful force which wecan put to work. A battery is also a source of dynamicelectricity which we can control. The chemical action ina battery produces electrical energy which has threeuseful applications in an automobile. It drives the electricmotor which starts the engine. It supplies energy to thespark plugs as heat for ignition, and the car lamps alsouse electrical energy for light. The car's generatorrecharges the battery and supplies the electric powerwhen the engine is running. Generators and batteries arethe most widely used sources of dynamic electricity.Now let's discuss static electricity and its effects.

1-5. The effects of static electricity can be observedin dry weather when you run a comb through your hair.The crackling you hear is the result of small discharges ofelectricity, and in a dark room you can see the tinyflashes of light a mirror. Lightning in a summer storm isthe violent discharge of tremendous static charges.

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Figure 1. Structure of atoms compared to earth and sun.

A charge accumulates over a period of time, and when itbecomes great enough to overcome the resistance of theair, a bolt of lightning occurs. Static electricity is theresult of friction which dislodges enough electrons toform a charge. When the charge becomes very great, theaccumulated energy is released in the form of electricalenergy accomplished by lightning and thunder.

1-6. The next discussion will cover the three mostcommon terms in electricity: “voltage,” “current,” and“resistance.” These three words are probably the mostimportant in electrical fundamentals. If you understandthe relationship between voltage, current, and resistance,you will have a good foundation on which to build yourknowledge of electricity. Therefore, it is important thatyou learn the meaning of these terms. Since electricitycannot be seen, we will present visual comparisons tohelp you in understanding the relationships.

1-7. Voltage is one of the several terms which meanthe same thing. These terms are: “voltage,” “potential,”“electromotive force (emf),” “potential difference,” and“electrical pressure.” The last term, “electrical pressure,”comes close to telling what voltage is. For example, thevoltage of a battery is like water pressure in a hose whenthe nozzle is closed. This is called potential energy, notperforming work. When the nozzle is opened, the wateris forced out by the pressure, thus doing work. This maybe related to closing an electrical switch, such as turningon your automobile lights. The potential energy of your

battery is then released, performing the work of lightingthe lights. The voltage is expended in the lights in theform of heat and light. Remember that voltage iselectrical pressure.

1-8. The current flow is made possible by closingthe switch which lowers the resistance to the voltage.Since this circuit has a relatively high resistance, thelamps could be burned for several hours before thebattery would be discharged. The starter for the enginehas a very low resistance, so it will draw a large currentfrom the battery. It uses so much energy that the batterymay become completely discharged by operating thestarter for just a few minutes. This is reasonable becausethe starter is doing more work (converting electricalenergy into mechanical energy) than are the car lights.With the foregoing discussion in mind, let us nowconsider concise definitions of our electrical terms.

Voltage is electrical pressure.Current is the movement of electrons.Resistance is the opposition to current flow.1-9. Voltage is measured in volts. Current is

measured in amperes. Resistance is measured in ohms.One volt is the electrical pressure required to cause 1ampere of current to flow through a resistance of 1 ohm.Scientists have made experiments which show that 6280trillion electrons pass a given point each second whenthere is 1 ampere of current in a circuit.

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1-10. Resistance to electric current is present in allmatter, but one material may have much more resistancethan another. Air, rubber, glass, and porcelain have somuch resistance that they are called insulators and areused to confine electricity to its proper circuit. Therubber covering on the wires to an electric lamp preventsthe wires from touching each other and causing a shortcircuit. The rubber also protects a person who is usingthe lamp so that he does not receive an electric shock.Air acts as an insulator whenever a light switch is opened.Air fills the gap between the open contacts of the switch,and no current flows because of the high resistance.However, even air may at as a conductor if the voltage is

high enough; otherwise, there could not be the electricaldischarge which appears in a lightning strobe.

1-11. Metals are good conductors of electricity butsome are better than others. Copper and silver are bothgood conductors of electricity because of their relativelylow resistance. Aluminum is not as good, but is used forlong overhead spans because of its light weight. Iron is apoor conductor, although it is used in combination withaluminum for added strength. Alloys of nickel andchromium are used in heater element to provide aspecific resistance which passes enough current to heatthe wires to a red glow. The alloy makes it possible tooperate at high temperatures without melting. Copper is

Figure 2. Copper wire size and resistance.

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relatively cheap and a good conductor; it is the mostwidely used for wiring circuits.

1-12. The resistance of a copper wire is determinedby three things: the cross-sectional area, the length, andthe temperature. In normal temperature ranges thechange in resistance is very small. The main factors ofresistance are the area or cross section of a wire and itslength. A wire with a larger diameter will have a greatercross-sectional area than will a smaller wire, andconsequently less resistance. A long wire will have moreresistance than a short one. Figure 2 shows therelationship between wire size and resistance. The firstcolumn gives the wire by number. A No. 40 wire isabout the diameter of a hair. Sizes larger than No. 4/0(spoken as four aught) are given in thousands of circularmil (350 MCM is 350,000 circular mils). The column atthe right gives the resistance in ohms for 1000 feet ofwire. One thousand feet of No. 10 copper wire has aresistance of about 1 ohm. The safe current carryingcapacity is given in three columns which show the effectsof insulation and conduit on the heat radiation ability ofthe conductor.

1-13. Magnet Characteristics. Magnetism relatedto electricity as heat is related to light. Whenever light isproduced, we have heat; and wherever electricity isproduced in the form of an electric current, we havemagnetism. However, heat can be made without visiblelight and magnetism can be detected without an electriccurrent. The effects of magnetism make a good startingplace toward an understanding of electricity. Many ofthe fundamental laws can be demonstrated by simpleexperiments which you can perform for yourself.

1-14. A magnetic compass needle, a bar magnet, andsome iron filings are the main things required. Thecompass needle will point toward the magnetic poles ofthe earth unless iron or steel objects are close enough to

Figure 3. Attraction and repulsion between magnets.

Figure 4. Pattern of a magnetic field.

affect it. When the north pole of a bar magnet isbrought close to the north pole of the compass needle,they will repel each other, as shown in figure 3; but thereis a strong attraction between a north pole and a southpole. This illustrates the fundamental law of magnetismwhich says that like poles repel while unlike poles attract.Between two magnets there is a magnetic field made upof lines of force.

1-15. This field around a magnet can be shown byplacing a sheet of glass or paper over a bar magnet. Asiron filings are sprinkled over the surface, they assume adefinite pattern, as shown n figure 4. The magnetic fieldis strongest at the poles of the magnet, where the lines offorce are bunched closely together. Lines of force followa uniform distribution and never cross each other. Amagnetic field may be distorted by iron or influenced byanother magnetic field. A piece of soft iron willconcentrate the lines of force in a field. In the samemanner, two unlike poles brought near each other willhave their fields linked up in common with each other.

1-16. Lodestone is a natural magnet which has beenknown for many centuries. From it the first compassneedles were fashioned. Artificial magnets are made byexposing metal to a strong magnetic field. Hardened ironwill retain magnetism over a long period of time. Alloysof aluminum and nickel make even stronger magnets.

1-17. The relationship between electricity andmagnetism can be demonstrated by a strong electriccurrent passing through a conductor. If iron filings aresprinkled over a piece of cardboard, as shown in figure 5,they will show a pattern of rings surrounding theconductor. A sensitive compass held near the wire willline up at right angles to the wire, showing that the linesof force have a definite direction. The compass needle

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will swing around 180° if the current in the conductor isreversed. This requires direct current (dc) such as we getfrom a battery. The current from a battery is said tohave only one direction, so it is called direct current. Byreversing the connections of a circuit to a battery, thecurrent in that circuit may be made to take the oppositedirection.

1-18. The magnetic field produced by a singlestraight conductor is relatively weak. However, the fieldcan be concentrated by forming the conductor into a coil.In this form a coil carrying an electric current shows amagnetic pattern similar to that of a bar magnet. Thecoil develops a north pole at one end and a south pole atthe other end. The polarity may be determined by theleft-hand rule which states, “If the coil is grasped withthe left hand with the fingers pointing in the direction ofelectron flow (negative to positive), then the thumb willpoint toward the north pole of the coil.” Electrons havea negative charge so they are attracted by a positivecharge. Consequently, the electron movement in acircuit is from negative to positive. The electronmovement in the conductor is indicated by two arrowsfigure 6.

1-19. Most coils are formed around an iron corebecause the core intensifies the magnetic field. The coilwith its iron core is called a solenoid. Air offersresistance to the lines of force, which is called reluctance.Iron has less reluctance than air so that the lines of forcewill choose a path through iron rather than air whenthere is a choice. Forming the iron into the shape of ahorseshoe makes less distance between the poles of amagnet, and the field is more concentrated. Soft iron isused for the core in electromagnets, as it will lose itsmagnetism when the current in the coil stops. The coreis

Figure 5. Electric current produces magnetic field.

Figure 6. Magnetic field produced by a coil.

built up with thin sheets of soft iron which serve toinsure the loss of magnetism when the magnetizing forceis removed. An example of this is an electromagnet usedfor picking up and moving scrap iron in a salvage yard.The magnet is hung from a crane and may pick up a tenor more of iron at one time. When the load is movedinto position to be dropped, the current to the coils isshut off. The loss of magnetism in the core allows theload to fall. The strength of the field of anelectromagnet is determined by the number of turns ofwire in the coils and the magnitude of the current.

1-20. Electron Movement and Effects. Electronsflowing through conductors cause several effects. Weshall discuss some of these briefly.

1-21. Heat. Heat is generated as the electrons flowthrough the conductor. The electric coffeemaker, electricstove or heater, and such items are examples of thiseffect that we see each day. Light is a side effect of theheat generated.

1-22. Light. An incandescent lamp is made up of afilament (conductor) inclosed in an evacuated envelope.As current passes through the filament, it is heated to thepoint of glowing. If no air is allowed into the envelope,the filament will last a long time.

1-23. When electrons flow through an ionized gas atthe right pressure and value, the gas will glow. Also, if astream of electrons strikes certain compounds, thecompounds will glow. Your TV picture gives a picturebecause of this effect.

1-24. Chemical. The chemical effect of electronmovement is important. If electrons are forced to movethrough a solution of certain chemicals, one of theelements in the solution will come out of the solution inits natural state.

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Figure 7. Basic electrical symbols.

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Thus, if an electric current is sent through a solution ofcopper sulphate, pure copper is deposited on one of thecontacts immersed in the solution. A stream of electronsreaching a contact immersed in a solution can change thechemical makeup of the contact.

1-25. Magnetism. Magnetic field, identical to thosediscussed previously are produced as a direct result ofelectron movements within a conductor.

1-26. Electromagnetic Fields. The magnetic fieldsproduced by electric currents are called electromagneticfields and are composed of lines of force like all othermagnetic fields. For example, in the field around astraight wire (conductor) carrying current the lines offorce are concentric circles. The force of the field isstrongest close to the wire, and it weakens rapidly thegreater the distance from the wire.

1-27. To determine the direction of the magneticfield about a current-carrying wire, use the left-handthumb rule which states, “Hold your left hand as ifgrasping the wire in such a way that your thumb points inthe direction of the current (electron) flow. The fingersof your left hand will then point in the direction of themagnetic field about the wire.”

1-28. The magnetic field associated with a loop ofwire is much the same as the field of a bar magnet. Theloop has poles similar to those of a bar magnet, with linesof force emerging from the north pole and entering thesouth pole. The left-hand rule applied to the loop of wirewill show you which is the north and which is the southpole.

1-29. If equal currents pass through a coil of wireconsisting of 8 closely wound turns and through a single-turn loop of the same diameter as the coil, the magneticfields will be almost identical in direction at every point.However, the magnetic field strength of the 8-turn coilwill be approximately 8 times that of the single loop.This is because the fields of the 8 turns are virtuallyparallel to each other at every point and their effects arecumulative at every point.

1-30. If you spread out the 8 turns into a helical coilthe magnetic field between the turns will be very weak.This is because the fields of adjacent turns will beopposite in direction and will tend to cancel each other.Inside and outside the coil they will be strong, for theywill be cumulative. The net result will be a strong fieldof fairly uniform intensity, represented by nearly straightlines of force both inside and outside the coil.

1-31. Both of the coils, the one closely wound andthe other spread apart, will each have a north pole at oneend and a south pole at the other. The direction of thefield will depend upon the direction of the current flow.

1-32. Safety. Anyone working with electricity mustalways be on his guard because of the dangers involvedwith electricity. Follow all rules. The basic rule is tokeep clear of lines or equipment when they are energized.Do not put yourself in such a position that your bodymay become part of the circuit. Rules cannot be writtento cover every situation; your own good judgment mustgovern your actions. The man who always practicessafety will establish good working habits so that he willnaturally do his work in a safe manner. The man whoneglects safety is a menace to himself and to thoseworking around him. Carelessness or a devil-may-careattitude should not be tolerated; either will eventuallylead to the destruction of life or property.

1-33. Study the information in figure 7 so that youcan recognize and identify each item. These symbols willbe used in this chapter to make schematic diagrams ofcircuits. The purpose and application of these device willbe explained in the discussion of circuits.

1-34. An example of the use of symbols is shown infigure 8. The upper part shows a picture of a toaster, apercolator, and a hot plate. Each of these has aresistance element which converts electricity into heatwhen the appliance is plugged into an outlet. The lowerpart of the figure show how these items would be repre-

Figure 8. Comparison between picture and symbolrepresentation.

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Figure 9. Inducing voltage by moving a conductor through a field.

sented in a schematic diagram. Each item is shown bythe same resistance symbol and must be identified withlabels to distinguish which is which. Notice how muchsimpler the schematic diagram appears and yet it conveysthe same information from an electrical standpoint as themore complex picture. You could easily draw thediagram in less than a minute and it would tell anothertechnician the same story - that there were threeappliances connected to a suitable source.

2. Production of Electromotive Force

2-1. A generator is a machine which convertsmechanical energy into electrical energy. First, thegenerator must have some source of mechanical energy.The type of machinery used to supply this energy to thegenerator is usually called the prime mover.

2-2. There are a number of methods used as primemovers. Water power (hydroelectric) normally has lowoperating costs, but high installation costs. Steam power(steam turbine) has a low installation and operating costwhen used for plants of 15,000-kw capacity or more.Diesel engines are used a great deal h plants where thecapacity required is from 2,000 w to 15,000 kw.However, there are low-speed and high-speed dieselengines. The high-speed diesel engine has a lowerinstallation cost than the low-speed type, but its life is notas long. Gasoline engines should not be chosen to drivegenerators in plants which require continuous powerbecause their fuel and maintenance costs are too high.The gasoline engines are usually used for small portableunits.

2-3. The electrical power output from a generatormay be either direct current (dc) or alternating current(ac), depending upon the construction. However, inprinciple, the rotating coils and the magnetic fieldthrough which they turn are the same for both types ofgenerators. The primary difference between ac and dcgenerators is the method by which the current is takenfrom the machine.

2-4. In a generator we have two set of coils and afield: one set of coils is in motion and the other set ofcoils acts as an electromagnet to set up a magnetic field.Figure 9 shows how a conductor moving across amagnetic field has a voltage induced in it. Thegalvanometer connected to the conductor has the zeroposition of the pointer in the center of the scale so that itcan read current in either direction. As the conductor ismoved upward through the field, the galvanometerneedle is deflected to the left. When the conductor ismoved downward, the galvanometer needle is deflectedto the right, showing that the direction of current in theconductor is reversed.

2-5. Direct-Current Generator. A simplifieddiagram of a dc generator is illustrated in figure 10. Aloop of wire represents the conductor that rotates in themagnetic field. The ends the loop terminate in two copperhalf rings which are insulated from each other. Fixedbrushes make a contact with the copper to conductelectricity to the external circuit. The loop is rotated aclockwise direction. In position A, the lines of force arenot being cut by the armature conductors but no voltage isproduced. In position , with the black half of the armatureconductor

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Figure 10. Simplified diagram of a direct-currentgenerator.

toward the north pole and the black half-ring against thenegative brush, the armature conductor is cutting themaximum lines of force. At this position maximumvoltage is induced into the armature conductors with thecurrent flow through the galvanometer as indicated infigure 10. At position C, the armature conductor hasrotated 180° from position A and again no voltage isproduced. In position D, with the white half of thearmature conductor toward the north pole and with thewhite half-ring against the negative brush, the armatureconductor again is cutting the maximum lines of force,with maximum voltage being induced into the armatureconductors and with the current flow through thegalvanometer in the same direction as position B. Checkthe black brush in the figure at positions B and D andyou will see that the sides of the armature conductorchange but the brushes are stationary; they deliver directcurrent because either armature conductor in contact withthe black brush will have the same direction of motionacross the field.

2-6. A direct-current generator is quite differentfrom the working model shown in figure 10. Instead ofpermanent magnet, strong electromagnets are used. Thestrength of the field can be controlled by changing thecurrent in the field coil A variable resistance in the fieldcircuit makes it possible to control the voltage output ofthe generator. Instead of a single loop, there are manycoils of wire in the rotor. The ends of each coilterminate in opposite copper segment. These coppersegments are formed in a ring called the commutator.The rotor assembly illustrated figure 11 is an armature fora dc generator.

2-7. The ends of the armature shaft ride in bearings.The three main parts of a generator are the stator, therotor, and the end bells. The main frame of thegenerator holds the stator or field. This frame supportsthe end bells which carry the bearings. One end bellcontain the brush rig which holds the brushes. Thevoltage generated is controlled by a rheostat in the fieldcircuit that changes the strength of the electromagnets.A change in speed would also change the voltage, but itis much simpler to control by resistance.

2-8. Alternating-Current Generator. Asimplified diagram of an ac generator is shown figure12. The difference between the dc generator and theac generator is in the method used to deliver thecurrent to the brushes. In the ac generator, slipringsare used instead of a commutator. This means thatthe same side of the loop delivers current to the samebrush re-

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Figure 11. DC generator armature.

gardless of rotation; otherwise the operation is the same.2-9. The illustration shows the loop turning in a

clockwise direction. At position A, the lines of force arenot being cut by the armature conductor so no voltage isproduced. At position 3, the armature conductor iscutting the maximum lines of force, and thegalvanometer indicates the direction of current flow bythe needle pointing to the right. At position C, thegalvanometer again shows zero because the lines of forceare not being cut by the armature conductor. At positionD, the armature conductor are again cutting themaximum lines of force, and the galvanometer againshows a current flow but in the opposite direction. Whathappened? At position B, the black side of the loop ismoving down through the field and the black slipring isnegative, sending current toward the meter. At positionD, the black side of the loop is moving up through thefield. Now the black slipring is positive. Current isdirected from the white slip ring to the meter and back.The direction of current in the loop reversed itself andthe same is true in the external circuit to the meter. Theloop in the dc generator operated the same way but thecommutator acted as a mechanical device to direct thecurrent in only one direction to the external circuit.

2-10. The output frequency, or cycles, of an acgenerator is determined by it speed and the number ofpoles. A two-pole machine must be driven at 3600 rpmto produce 60 cycles per second. A four-pole machinerequires a speed of 1800 rpm for a frequency of 60cycles. The formula for frequency is

where f is the frequency, P is the number of poles, and Sis the speed rpm. The output voltage is controlled in thesame manner as described for a dc generator. A rheostatin series with the field is used to change the strength ofthe field magnet; the stronger the field, the greater thevoltage generated.

2-11. The simple ac generator discussed here wouldproduce single-phase current, as there is only one loop orwinding. A three-phase generator requires three sets ofwindings and each winding produces one phase. Thewindings are physically displaced from each other 120°apart so that maximum voltage in one winding isgenerated at a different time from that in the otherwindings. At least three wires are needed to deliverthree-phase electrical power from the generator toequipment. A single-phase voltage and current isdeveloped between any two of the wires. Phases may bedesignated by number or as A, B, C, for identification.Figure 13 shows the pattern of a three-phase current forone complete cycle. A peak occurs every 60°, or 6 timesfor each cycle. The same pattern of rise and fall shouldbe used to illustrate the cycle of three-phase voltage.

3. Direct Current Fundamentals

3-1. In order for current to flow, two things areessential: there must be a source of electrical pressure(voltage) and there must be a complete circuit. Thesource of voltage may be a battery, a generator, or someother device. The complete circuit requirement meansthat there must be a complete path from the negativeterminal through the load and back to the positiveterminal of the source. The complete path should allowthe electrons to flow freely to the load, do their work inthe load, and then move freely back to the source.

3-2. However desirable this condition is, it cannotbe completely achieved since no material used as aconductor (wire) allows the electrons to move withcomplete freedom. There is always some resistance tothe electron flow. All conductors have some resistance;just how much they have depends on the size and length ofthe con-

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Figure 12. Simplified diagram of an alternating-currentgenerator.

Figure 13. One cycle of a three-phase current.

ductors as well as on the materials of which they aremade.

3-3. The source of voltage is any device which hasan excess of electrons in one place over the number ofelectrons in another place. Connecting the two places bymeans of an electrical circuit, including resistance,permits the two places to try to equalize the number ofelectrons. The movement of electrons that results fromthis attempt is what is known as current.

3-4. Ohm’s Law and DC Circuit. Since Ohm's lawcontains two separate thoughts, it may be expressed inthe following two statements: (1) Current in anyelectrical circuit is directly proportional to the voltage, and(2) current in any electrical circuit i inversely proportionalto the resistance. Ohm's law is more generally stated asfollows: The current in a circuit is equal to the voltagedivided by the resistance. Mathematically, it is expressedas:

(1)

In this equation, I stands for the current in amperes, Efor the voltage in volts, and R for the resistance in ohms.Thus, if the source of potential is a 6-volt battery and theelectrical device is a bulb having 3 ohms of resistance,the current will be:

3-5. The equation for Ohm's law can be convertedmathematically to read as follows:

E = I X R (2)

By use of this equation, you can determine the voltageacross a component of a circuit if you know the unit'sresistance and the current flow through it. Thus, if youknow that the current through a lamp is 2 amperes andthe resistance of the amp is 3 ohm, you know that thevoltage across it must be 3 X 2, or 6 volts.

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3-6. The equation for Ohm's law can be convertedmathematically in still another way to read:

(3)

Using equation 3, you can determine the resistance ofany circuit component if you know the voltage across itand the current flowing through it. Suppose you knowthat the voltage across a lamp is 6 volts and the currentthrough it is 2 amperes. You can find the lamp'resistance by substituting in equation 3:

3-7. Using these three equations enables you to findany one of the three quantities - voltage, current, orresistance - if you know the other two.

3-8. Series Circuits. A series circuit is one inwhich there is only one path through which the currentcan flow. In figure 14 three resistances and a battery areconnected to form a series circuit. Since there is but onepath for the current all of the current passes througheach resistance and the current is the same throughoutthe entire circuit, or

It = I1 = I2 = I3, etc. (4)

3-9. The total voltage drop in the series circuit isequal to the sum of the voltages (voltage drops) acrossthe individual resistors, or

Et = E1 + E2 + E3, etc. (5)

3-10. The total resistance of the circuit is equal tothe sum of the resistances of the individual units, or

Rt = R1 + R2 + R3, etc. (6)

3-11. If one of the devices in a series circuit burnsout, there is no longer a complete path for the currentand, therefore, the other devices the circuit will notoperate.

3-12. Problem: In figure 14, three resistances areconnected in series across a 24-volt power source. Thevoltages and currents are measured and found to be asindicated in the illustration. Find:

a. The total voltage drop.b. The total current.c. The resistance of each unit.d. The total resistance.

Figure 14. Series circuit.

Solution:

a. Using equation 5:E = 8 + 12 + 4 = 24 volts

b. Using equation 4:It = 4 = 4 = 4 amperes

c. Using equation 3, the resistance of each unit iscomputed as follows:

d. Using equation 6:

Rt = 2 + 3 + 1 = 6 ohms

Check:Using equation 3, the total resistance can also be

computed as follows:

3-13. Parallel Circuits. In a parallel circuit, two ormore electrical devices provide independent paths throughwhich the current may flow. The voltage across eachdevice so connected in parallel is the same, or

Et = E1 = E2 = E3, etc. (7)

3-14. The total current in the circuit is equal to thesum of the individual currents flowing through theparallel-connected devices, or

It = I1 + I2 + I3, etc. (8)

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3-15. Thus, the total amount of current in a parallelcircuit is greater than the current in any one individualbranch or leg, and consequently the total resistance mustbe less than the value of the smallest resistance in thecircuit. The greater the number of electrical devices orresistors connected in parallel in a given circuit, thegreater will be the total current, and the smaller will bethe total resistance of the circuit.

3-16. Electrical devices are connected in parallel inany installation in order to: (1) decrease the totalresistance of the circuit and (2) allow the units to operateindependently of each other. In a parallel circuit, if oneunit burns out it does not affect the operation of theother units; one path is broken but the other circuits arestill complete.

3-17. There are several ways to calculate the totalresistance of a parallel circuit. We shall show the simplerway first, which is the product over the sum method, andthen give you the more complex general rule.

3-18. To calculate the total resistance of the parallelcircuit shown in figure 15, use the following equation andsolve for the equivalent resistance of only two paths at atime.

(9)

3-19. When the load units that are connected inparallel all have the same resistance value, the previousequation may be simplified to read:

(9A)

3-20. Problem: In the illustration accompanying theprevious discussion, three load units are connected inparallel. Using the resistance values indicated, find thetotal resistance.

Solution:a. Using equation 9, for the first two paths

b. Since 3 ohms is the equivalent resistance of thefirst two paths you may substitute a 3-ohm resistor forthem, and adding the 6-ohm resistor of the third pathredraw the circuit as shown at the right in the illustration.

c. Then, combing R(1 and 2) with R3 and usingequation 9 again, you have

3-21. The general equation for finding the totalresistance in a parallel circuit is known as the reciprocalmethod. It involves determining the reciprocal of thesum of the reciprocals of the individual resistances. Inother words, find a common denominator and divide theresistances

Figure 15. Parallel circuit.

13

into the common denominator, then add and invert, anddivide this sum to find the total resistance.

(10)

3-22. Using equation 10, the total resistance can becomputed as follows:

3-23. Series-Parallel Circuit. As shown in figure16, in a series-parallel circuit some of the units areconnected in series with each other, while other units areconnected in parallel. To solve a series-parallel problem,first convert it to a series circuit by substituting anequivalent resistance for the parallel resistances; thensolve the series circuit problem as explained previously.

3-24. Problem: In the illustration of the series-parallelcircuit a resistor is connected in series with four lampswhich are connected in parallel with each other. Thevoltage and resistances were measured and found to be asindicated. Find the current through the various parts ofthe circuit.

Solution:a. The resistance of each lamp is 4 ohms.

Therefore, using equation 9A, the equivalent resistance ofthe four lamps in parallel is

b. Substituting a 1-ohm resistor for the four lampsand using equation 6, you find the total resistance of thecircuit as follows:

R4 = 5 + 1 = 6 ohm

c. Using equation 1, you compute the total currentin the circuit to be

d. Since the total current must flow through theseries resistor, the current flow through it must be 4amperes.

e. Since the total current flowing through the fourlamps is 4 amperes and since they all have the samevalue of resistance, the current must divide evenly amongthe lamps and is therefore found to be 1 ampere througheach lamp circuit.

3-25. Power. Besides the current, voltage, andresistance of a circuit, the power must also be considered.Power is defined as the rate of doing work, and it ismeasured in a variety of units. An electric motor, forexample, is rated in terms of horsepower. Onehorsepower is the rate of doing work when a 550-poundweight is raised a distance of 1 foot in 1 second. Somemotors develop 5000 or more horsepower. Electrical

Figure 16. Series-parallel circuit.

14

Figure 17. Sine wave of current and voltage.

power is generally expressed in terms of watts. A watt isthe power consumed in a circuit through which 1 ampereflows under a pressure of 1 volt. One horsepower equals746 watts.

3-26. Most electrical devices are rated according tothe voltage that should be applied to them and alsoaccording to the amount of power they require. Forexample one lamp might be rated as a 115-volt, 40-wattlamp, while another might be rated as a 115-volt, 20-wattlamp. This means that both lamps are to be operated ona 115-volt circuit, but that twice as much power isrequired to operate the first lamp as the second.

3-27. You can compute the wattage of an electricalunit - that is, the power it requires - by multiplying thevalue of the current flowing through it by the value ofthe voltage applied to it.

P = I X E (11)

Thus, a starter motor drawing 70 amperes at a potentialof 24 volts is using 1680 watts of electrical power. Toconvert electrical power (wattage) to horsepower, dividethe electrical power rating by 746. Thus, by dividing1680 watts by 746-watts (the electrical equivalent of 1horsepower) you will find that the starter motor willdevelop approximately 2.25 horsepower.

4. Alternating-Current Fundamentals

4-1. In a dc circuit, current moves in one direction,from the negative terminal of the source through thecircuit to the positive terminal. In ac circuits, the currentflows first in one direction and then in the oppositedirection, thus the name “alternating current.”

4-2. Alternating current has largely replaced directcurrent for a number of reasons, namely: (1) ac voltagescan be increased or decreased very efficiently withtransformers, (2) ac devices are much simpler andconsequently are less prone to trouble than are dcdevices, (3) ac units are much lighter, and (4) theyoperate more efficiently.

4-3. Most electrical appliances manufactured in theUnited States have a small “data plate” which gives theelectrical information necessary for connecting theappliances to the proper electrical circuits. This data plateusually gives the voltage, frequency (cycles per second),horsepower (size of motor) or watts (for heating units),amperes, ac or dc, and the power factor. If you connectelectrical appliances per the information on the data plate,they usually give a long life of uninterrupted service.

4-4. Phase of Current and Voltage. When currentand voltage pass through their zero value and reach theirmaximum value at the same time, the current andvoltage are said to be in phase. If the current and voltagepass through zero and reach their maximum values atdifferent times, the current and voltage are said to be outof phase. In a purely inductive circuit the current reachesa maximum value later than the voltage, lagging thevoltage by 90°, or one-fourth of a cycle. In a circuitcontaining only capacitance, the current reaches itsmaximum ahead of the voltage, and the current leads thevoltage by 90°, or one-fourth of a cycle.

4-5. Figure 17 shows graphically the in-phasecondition and the effect of inductance and capacitanceon this phase relationship. The current will never lead orlag the voltage by exactly

15

90° because of the resistance of the conductor. Thenumber of degrees by which the current leads or lags thevoltage in a circuit depends on the relative amounts ofresistance, capacitance, and inductance in the circuit.

4-6. Inductance. When an alternating current flowsthrough a coil of wire, it sets up an expanding andcollapsing magnetic field about the coil. The expandingand collapsing magnetic field induces a voltage within theconductor proper which is opposite in direction to theapplied voltage.

4-7. This induced voltage opposes the appliedvoltage, thus serving to lessen the effect of the appliedvoltage. This results in the self-induced voltage tendingto keep a current moving when the applied voltage isdecreasing and to oppose a current when the appliedvoltage is increasing. This property of a coil whichopposes any change in the value of the current flowingthrough it is called inductance.

4-8. The inductance of a coil is measured in henrys,and the symbol for inductance is L. In any coil theinductance depends on several factors, principal of whichare the number of turns of wire in the coil, the cross-sectional area of the coil, and the material in the centerof the coil, or the core. A core of magnetic materialgreatly increases the inductance of the coil.

4-9. Remember, however, that even a straight wirehas inductance, small though it may be when comparedto that of a coil. All ac motors, relays, transformers, andthe like contribute inductance to a circuit.

4-10. Capacitance. Another important property ofac circuits, besides resistance and inductance, iscapacitance. While inductance is represented in a circuitby a coil and resistance by a resistor, capacitance isrepresented by a capacitor. Any two conductorsseparated by a nonconductor constitute a capacitor. Thecapacitor is used in an electrical circuit to momentarilystore electricity, smooth out pulsating dc, give moretorque to a motor by causing the current to lead thevoltage (see fig. 17), reduce arcing of contact points, andhasten the collapse of the magnetic field of an ignitioncoil to produce a hotter spark.

4-11. Power in AC Circuits. In a dc circuit, wecalculate power by using equation 11, where the voltstimes the amperes equal the watts (power). Thus, if 1ampere flows in a circuit at a potential of 200 volts, thepower is equal to 200 watts. The product of the voltageand the amperage is the true power of the circuit in thiscase.

4-12. In an ac circuit, however, the voltmeter indicates theeffective voltage and an ammeter indicates the effectivecurrent. The product of these two indicate what is calledapparent power. The relationship between true power,reactive power, and apparent power is shown graphicallyin figure l8. Only when the ac circuit is made

Figure 18. Power relations in an ac circuit.

up of pure resistance is the apparent power equal to thetrue power.

4-13. When there is capacitance or inductance in thecircuit, the current and voltage are not exactly in phasewith each other, and the true power is less than theapparent power. The true power is obtained by awattmeter indication. The ratio of the true power to theapparent power is called the power factor of the load andis usually expressed as a percentage. In equation formthe relationship is:

(12)

4-14. Problem: A 220-volt motor draws 50 amperesfrom the supply lines, but the wattmeter indicates thatonly 9350 watts are taken by the motor. What is theapparent power and what is the power factor of thecircuit?

Solution:a. Apparent power = 220 X 50 = 11,000 volt-

amperes.b. Using equation 12,

5. Transformers

5-1. A transformer is an apparatus which transformselectrical energy at one voltage into electrical energy atanother voltage. It consists of two coils which are notelectrically connected (except auto transformers) but arearranged so that the magnetic flux surrounding one coilcuts through the other coil upon buildup or collapse ofthe magnetic field. When there is an alternating currentin one coil, the varying magnetic flux

16

Figure 19. Voltage and current transformer.

creates an alternating voltage in the other winding bymutual induction. A transformer will also operate onpulsating dc but not on pure dc.

5-2. A transformer consists of three primary parts:an iron core, which provides a circuit of low reluctancefor the magnetic flux; a primary winding, which receivesthe electrical energy from the supply source; and asecondary winding, which receives electrical energy byinduction from the primary and delivers it to thesecondary circuit.

5-3. The primary and secondary coils are usuallywound, one upon the other, on a closed core obtainmaximum inductive effect between them. The turns ofinsulated wire and layers of the coil are well insulatedfrom each other by layers of impregnated paper or mica.The iron core is laminated to minimize magnetic currentlosses (eddy losses) and is usually made of speciallyprepared silicon steels since these steels have a lowhysteresis loss. (Hysteresis loss is the portion of themagnetic energy converted to heat and lost to the systemso far as useful work is concerned. It occurs withchanging magnetic polarity.)

5-4. There are two classes of transformer - voltagetransformers for stepping up or stepping down voltages,and current transformers which are generally used ininstrument circuits. In voltage transformers the primarycoils are connected in parallel across the supply voltage, asseen in figure 19. In current transformers the primarywindings are connected in series in the primary circuit.

5-5. Of the two types, the voltage transformer is themore common. There are also power-distributingtransformers for use with high voltages and heavy loads.Transformers are usually rated in kilovolt-amperes.

5-6. Principles of Operation. When an alternatingvoltage is connected across the primary terminals of atransformer, an alternating current will flow and self-induce in the primary coil a voltage which is opposite andnearly equal to the connected voltage. The differencebetween these two voltages will allow just enough currentto flow in the primary coil to magnetize its iron core.This is called the exciting (magnetizing) current.

17

Figure 20. Single-phase generator and load.

5-7. The magnetic field caused by the excitingcurrent cuts across the secondary coil and induces asecondary voltage by mutual induction. If a load isconnected across the secondary coil of the transformer,the load current flowing through the secondary coil willproduce a magnetic field which will tend to neutralize themagnetic field produced by the primary current. This, inturn, will reduce the self-induced (opposition) voltage inthe primary coil and allow more primary current to flow.

5-8. The primary current increases as the secondaryload current increases, and decreases as the secondaryload current decreases. When the secondary load isremoved, the primary current is again reduced to thesmall exciting current sufficient only to magnetize theiron core of the transformer.

5-9. Connecting Transformers in an AC Circuit.Before studying the various uses of transformers and thedifferent ways of connecting them, you shouldunderstand the difference between a single-phase circuitand a three-phase circuit.

5-10. A single-phase circuit is a circuit in which thevoltage is generated by an alternator, as shown in figure20. This single-phase voltage may be taken from asingle-phase alternator or from one phase of a three-phase alternator, as explained later.

5-11. A three-phase circuit is a circuit in which threevoltages are generated by an alternator with three coils sospaced within the alternator that the three voltagesgenerated are equal but reach their maximum values atdifferent times, as shown figure 21. In each phase of a60-cycle, three-phase generator, a cycle is generated every1/60 second.

5-12. In its rotation, the magnetic pole passes onecoil and generates a maximum voltage; one-third of acycle (1/180 second) later, this same pole passes anothercoil and generates a maximum voltage in it; and one-third of a cycle later, it passes still another coil andgenerates a

Figure 21. Sine wave of voltage outputs of single- andthree-phase generators.

maximum voltage in it. This causes the maximumvoltages generated in the three coils always to be one-third of a cycle (1/180 second) apart.

5-13. Three-phase motors and other three-phaseloads are connected with their coils or load elementsarranged so that three transmission lines are required fordelivery of power. (See fig. 22.) Transformers that areused for stepping the voltage up or down in a three-phasecircuit are electrically connected so that power isdelivered to the primary and taken from the secondary bythe standard three-wire system.

Figure 22. Three-phase generator with three conductors.

18

Figure 23. Step-down transformer, two-wire system.

5-14. However, single-phase transformers may beconnected across any two phases of a three-phase circuit,as shown figure 23. When single-phase loads areconnected to three-phase circuits, the loads are distributedequally among the three phases in order to balance theloads on the three generator coils.

5-15. Another use of the transformer is the single-phase transformer with several taps in the secondary.With this type of transformer, we can lower the voltageand also have several working voltages, as shown infigure 24. A center-tapped transformer powering a motorrequiring 220 volts, along with for lights requiring 110volts is shown in figure 25. The motor is connectedacross the entire transformer output, and the lights areconnected from the center tap to one end of thetransformer. With this connection we are using only halfof the secondary output.

5-16. This type of transformer connection is usedquite extensively because of the combinations of voltagesthat may be taken from one transformer. Variousvoltages may be picked off the secondary winding of thetransformer by inserting taps (during manufacture) atvarious points along the secondary winding. The variousamounts of voltage are obtained by connecting to anytwo taps or to one tap and either end, as shown aprevious illustration.

Figure 24. Multivoltage transformer secondary.

5-17. Transformers for three-phase circuit can beconnected in any one of several combinations of the wye(y) and delta (∆) connections. The connection useddepends on the requirements for the transformer.

5-18. Wye connection. When the wye connection isused in three-phase transformers, a fourth or neutral wiremay be used, as show in figure 26. The neutral wireserves to connect single-phase equipment to thetransformer. Voltages (120 v) between any one of thethree-phase lines and the neutral wire can be used forpower for devices such as lights or single-phase motors.Single- and three-phase equipment can be operatedsimultaneously, as show in figure 27.

5-19. In combination, all four wires can furnishpower at 208 volts, single and three-phase, for operatingsingle- and three-phase equipment such as motors orrectifiers with the center tap used as equipment ground.When only three-phase equipment is used, the groundwire may be omitted. This leaves a three-phase, three-wire system.

5-20. Delta connection. Figure 28 shows the primaryand secondary with a delta connection. Between any twophases the voltage is 240 volts. This type of connectionusing the three wires - A, B, and C - can furnish 240-volt, three-phase power for the operation of three-phaseequipment.

5-21. Wye and delta connections. The type ofconnection used for the primary coils may or may not bethe same as the type of connection used

19

Figure 25. Step-down transformer, three-wire system.

for the secondary coils. For example, the primary maybe a delta connection and the secondary a wyeconnection. This is called a delta-wye (∆-y) connectedtransformer. Other combinations are delta-delta, wye-delta, and wye-wye.

5-22. Current Transformers. Current transformersare used in ac power supply systems.

5-23. The current transformer is a ring typetransformer using a current-carrying power lead as aprimary (either the power lead or the ground lead of theac generator). The current in the primary induces acurrent in the secondary by magnetic induction.

5-24. The sides of all current transformer aremarked “H1” and “H2” on the unit base. Thetransformers must be installed with the “H1” side towardthe generator in the circuit in order to have properpolarity. The secondary of

Figure 28. Wye-to-wye connection.

the transformer should never be left open while thesystem is being operated; to do so could causedangerously high voltages and could overheat thetransformer. Therefore the transformer outputconnections should always be connected with a jumperwhen the transformer is not being used but is left in thesystem.

6. Electrical Meters

6-1. In the installation, inspection, maintenance, andoperation of electrical air-conditioning equipment, youwill often have to measure voltage, current, andresistance. A number of instruments have beendeveloped for this purpose.

Figure 2. Four-wire, three-phase wye system.

20

Figure 28. Delta-to-delta connection.

We will discuss these meters and their uses.6-2. Galvanometer. In electrical systems the

moving-coil galvanometer (D'Arsonval type) is used quiteextensively. This movement is used in such instrumentsas voltmeters, ammeters, thermocouple thermometers,and electrical tachometer.

6-3. Voltmeter. A voltmeter is an instrument usedto measure the difference in electrical potential, or thevoltage, between two point. (See fig. 29.) Notice infigure 29 the rotary switch which may be connected tovarious size resistors. These are in series with themovable coil to limit the amount of current flow through

Figure 29. Voltmeter.

Figure 30. Ammeter with an external shunt.

the meter circuit. If an unmarked voltage is to bemeasured, set the rotary switch to the highest resistanceand work down until the meter reads in a somewhat mid-position of full scale.

6-4. Ammeter. An ammeter is an instrument thatmeasures the amount of current flowing in a circuit.You may have a need for an ammeter with a range froma milliampere to 500 amperes. These meters may havean external shunt, as shown in figure 30, or they may beinternally shunted. Question: What is a shunt for?Answer: Very fine wire is used in the coil. This wire cancarry very little current without overheating - only a smallfraction of an ampere. A low-resistance shunt isconnected in parallel with the meter so that most of thecurrent bypasses the meter; only a very small portion ofthe total current flows through the coil. For example:When a 300-ampere ammeter and a 300-ampere shuntare connected into a circuit carrying 300 amperes, only0.01 ampere flows through the meter to give full-scaledeflection; the remaining 299.99 amperes flow throughthe shunt.

6-5. By applying the basic rule for parallel circuits,you can easily compute the value of a shunt resistorneeded to extend the range of an ammeter.

6-6. Ohmmeter. An ohmmeter is an instrumentused to measure resistance in ohms. Combinationvoltohmmeters and other multipurpose meters are usedmore than simple ohmmeters. The principle of operationof an ohmmeter is

21

Figure 31. Ohmmeter.

basically the same, regardless of whether the meter is aseparate instrument or is part of a multipurposeinstrument.

6-7. An ohmmeter contains a very sensitivegalvanometer. The scale on the dial is calibrated inohms. Maximum current flows through the circuit whenthere is a minimum amount of resistance between theohmmeter terminals. For this reason, zero is at the right-hand end of the scale. The ohmmeter does not have anevenly, graduated scale; frequently the right half of thescale will read to about 5000 ohms, while the left halfwill read 100,000 ohms or more. The left-hand end ofthe scale is sometimes marked “INF,” which means thereis infinite resistance between the terminals.

6-8. Some ohmmeters have three or even four poststo which the leads may be attached. (See fig. 31.) Theseposts may be marked in different ways on differentmeters, but for purposes of explanation let us consider ameter on which the posts are marked “C,” “RX1,”“RX10,” and “RX100.” If the leads are connected to Cand RX1, the resistance being measured is indicateddirectly on the scale. If the terminals are connected to Cand RX10, the reading on the scale must be multiplied by10 to give the actual resistance. If the terminals areconnected to C and RX100, the reading on the scalemust be multiplied by 100. Short the two leads together

and zero the meter with the zero adjustment. This mustbe done any time the lead is moved from one jack toanother.

CAUTION: Make sure the circuit to be measured isdead before using the ohmmeter.

6-9. Rectifier Meter. Alternating-current voltagesare often measured by rectifier type meters. A rectifiermeter is actually a dc meter with a rectifier added tochange the ac to dc. Without a rectifier, of course, a dcmeter would give no indication when applied to an accircuit. Generally, a copper-oxide rectifier connected as abridge provides the rectification. This is shown in figure32. Values of ac voltages indicated on the rectifier meterare effective values.

6-10. Wattmeters. Power in an ac circuit is notalways found by multiplying voltage by amperage as in adc circuit. Such a power computation can be made for accircuit only when the voltage and current are in phase,that is, when there is a purely resistive load. In practicethis condition seldom exists, since in almost all ac circuitsthe load is reactive because of the presence of inductanceand capacitance. The wattmeter, however, measures thetrue power consumed in a circuit by all electrical devicesregardless of the type of load.

6-11. Wattmeters may be used to measure powerconsumed in either single-phase or three-phase circuits inwhich the load is balanced. The single-phase wattmeterhas a high-resistance moving voltage coil for many turnsof fine wire and stationary coils, called current coils, oflow resistance with a few turns of heavy wire. Connectthe current coils in the line in series with the load, andthe voltage coil across the line.

6-12. A single-phase wattmeter may be connected tomeasure the power by a three-phase circuit. To do this,connect the current coil in one load line and the voltagecoil between the line and ground. This will give thepower in one phase. Multiply this by 3 to get the totalpower.

6-13. Three-phase wattmeters consist of two ormore single-phase movement with all the movingelements mounted on one shaft. Separate single-phasewattmeters can be used to measure power in three-phasecircuits by connecting two wattmeter in any two of thethree phases. In this case, add the two wattmeterreadings if the power factor of the load (motor) is greaterthan 50 percent (the power actor can be found on thenameplate or in the technical order). If the power factoris below 50 percent, the power input to the load (motor)is the difference between the two readings.

6-14. You can determine whether to add or subtractthe readings by the following: If both of the scalepointers deflect toward the top of the scale, add thereadings; if one tends to indicate a negative value, reverseeither the voltage or

22

Figure 32. Rectifier meter circuit.

current connections and subtract the reading of onewattmeter from the reading of the other.

6-15. Using Electrical Meters. Only two of themeters discussed in this chapter, the voltmeter and theohmmeter, are used to locate troubles in an electricalcircuit. How the meters are used for this purpose will beexplained in detail. However, before attempting to useany of the meters which have been discussed, you shouldfix firmly in your mind certain precautions concerningtheir use.

6-16. General precautions.(1) Never connect a voltmeter to a circuit having

a voltage that exceeds the voltmeter scale. If the voltageis unknown, start with a high scale and work down untilyou get the correct one.

(2) Never connect an ammeter into a circuitcarrying more current than the maximum reading on thescale of the meter.

(3) Always connect an ammeter in series with theunits in the circuit.

(4) Never connect an ammeter across theterminals

of a battery or generator, or any other place where youprovide a path through the meter from a source ofvoltage direct to ground. To do so would cause themeter to burn out immediately.

(5) Always check the rating of a meter before youuse it.

(6) Never use an ohmmeter to check an electricalcircuit until the source of voltage has been disconnectedfrom all parts of the circuit to be checked. Using theohmmeter in a live circuit would damage the meter.

(7) Always connect the voltage coil of awattmeter to the supply side of the current coil.

6-17. Voltmeter. The most common trouble foundin electrical circuits that are inoperative is an open circuit.This means simply that there is not a complete path forthe current to flow through as it should. The “open,” orthe place where the circuit is open, can be located witheither a voltmeter or an ohmmeter. If electrical power isavailable, use the voltmeter.

6-18. An open in a circuit may be located anywherein the circuit. It my be in the switch,

23

Figure 33. Continuity testing with a voltmeter.

24

fuse, wiring, or in the unit itself. If the fuse is burnedout, or open, you should inspect all of the circuit todetermine what caused the fuse to blow.

6-19. A trouble known as a short might have causedthe fuse to blow. A short is direct contact between thehot and negative or ground portion of the circuit. Sincethere is practically no resistance in this new or shortcircuit, the current flow increases immediately until itexceeds the capacity of the fuse and blows the fuse.

6-20. A voltmeter is always connected in parallelwith the unit being tested - that is, across the unit - or tothe points between which the difference of potential is tobe measured.

6-21. If you should accidentally connect thevoltmeter in series with the circuit, it wouldn't hurt themete because the high resistance in the meter would limitthe current flow. However, the units in the circuit wouldnot operate because of the low current

6-22. Locating an open with a voltmeter is simply amatter of checking to see how far voltage is present inthe circuit. Voltage will be present the circuit right up tothe point where the circuit is open.

6-23. When you have to check a circuit to find anopen, you can start at any point in the circuit. It islogical, of course, to check the fuse first and the unitsecond. As explained earlier, this will enable you to tellwhether the trouble is an open or a short.

6-24. If the fuse and the unit are both good, youmay have to check each end of each length of wire inthe circuit to find the open. Use the wiring diagram ofthe circuit as a guide. The important things are to knowwhat voltage reading you should have at each point in thecircuit and to recognize an abnormal reading when youget one. Figure 33 shows the voltage readings obtainedat different points in a circuit with an open fuse, an openlamp filament, and one with an open ground wire.

6-25. Ohmmeter. Before you use an ohmmeter tocheck a circuit, be sure there is no electrical power in thecircuit. It was explained earlier in this chapter that usingan ohmmeter in a live circuit could damage the meter.

6-26. If you use a multirange ohmmeter to checkresistance, choose a scale on the ohmmeter which youthink will contain the resistance of the element you aregoing to measure. In general, select a scale in which thereading will fall in the mid-scale range. Short the leadstogether and set the meter, with the zero adjustment, toread zero ohms. If for any reason you change scales,readjust the meter to zero ohms.

6-27. Connect the leads across the circuit. Infiniteresistance indicates an open circuit. A reading other thaninfinite resistance indicates continuity.

6-28. Let's simulate locating the troubles with theohmmeter. First we must be sure we have disconnected

the power from the circuit to permit use of theohmmeter. Now, with one lead connected to negative orground, check at various points with the other lead. Ifyou start at the point where the circuit is grounded, themeter will read zero ohms.

6-29. After you pass the first resistance the meterwill read that resistance. When you get the first readingof infinite resistance, this will indicate that the open isbetween that point and the point where you got the lastnormal reading.

Figure 34. Single-phase motor with capacitor startingwinding.

25

6-30. When you check continuity in a parallelcircuit, isolate the unit you are checking so the ohmmeterwill not show the resistance of parallel paths.

7. Motors

7-1. In this section we will discuss some of theelectrical motors that you may encounter in your job.We will discuss ac single and polyphase induction motors,ac/dc universal motors, and synchronous motors.

7-2. Principles of Operation. The speed of rotationof an ac motor depends upon the number of poles andthe frequency of the electrical source of power:

7-3. Since an electrical system operates at 60 cycles,an electric motor at this frequency operates about 2 1/2times the speed of the old 25-cycle motor with the samenumber of poles. Because of this high speed of rotation,60-cycle ac motors are suitable for operating largerrefrigeration systems.

7-4. Alternating-current motors are rated inhorsepower output, operating voltage, full-load current,speed, number of phases, frequency, and whether theyoperate continuously or intermittently.

7-5. Single-Phase Induction Motors. All single-phase induction motors have a starting winding (see fig.34) since they cannot be started with only the single-phase winding on the stator. After the motor has started,this winding may be left in the circuit or be disconnectedby a centrifugal switch.

7-6. Both single-phase and three-phase motorsoperate on the principle of a rotating magnetic field. Asa simple example of the principle

Figure 35. Production of a rotating magnetic field.

26

Figure 36. Squirrel-cage induction-motor rotor.

of the rotating field, imagine a horseshoe magnet heldover a compass needle. The needle will take a positionparallel to the magnetic flux passing between the twopoles of the magnet. If the magnet is rotated, thecompass needle will follow.

7-7. A rotating magnetic field can be produced by atwo- or three-phase current flowing through two or moregroups of coils wound on inwardly projecting poles of aniron yoke. The coils on each group of poles are woundalternately in opposite directions to produce oppositepolarity, and each group is connected to a separate phaseof voltage.

7-8. You can understand this action with the aid offigure 35, which shows a four-pole stator field energizedby two windings connected to two separate phase voltage.Winding No. 1 of the motor is 90° out of phase withwinding No. 2, which causes the current in winding No.1 to lead the current in winding No. 2 by 90°, or by1/240 second, assuming the frequency of the ac powersupply is 60 cycles per second. Winding No. 1 can bereferred to as phase 1, and winding No. 2 as phase 2.

7-9. The direction of the magnetic field is indicatedby a magnetic needle (considered as a north pole forclarity). The needle will always move to a position whereit will line up with the magnetic flux passing from pole topole. Notice the phase relationship of the two voltageswhich are applied to the two phase windings of the field.Phase 1 supplies current to the coils on poles A and A',and phase 2 supplies current to the coils on poles B and

B'. The two currents are 90° out of phase, with phase 1leading.

7-10. At position B, the current in phase 1 at amaximum and the poles of A and A' are fullymagnetized. The poles of coils B and B' are notmagnetized, since the current in phase 2 is zero.Therefore the magnetic needle points in the directionshown. At position C, the current coils A and A', phase1, has decreased to the same value to which the currentin coils B and B', phase 2, has increased. Since the fourpoles are now equally magnetized, the strength of thefield is concentrated midway between the poles, and themagnetic needle take the position shown.

7-11. At position D, the current of phase 1 is zerothrough coils A and A', and there is no magnetism inthese coils. There is maximum current through coils Band B', the magnetic field strength of B and B' ismaximum, and the magnetic needle takes the crosswiseposition. This action is repeated during successive cyclesof the flow of the alternating currents, and the magneticneedle continues to revolve in the same direction withinthe field frame as long as the two phase currents aresupplied to the two sets of coils.

7-12. In an induction motor with two poles for eachphase winding, the north pole would glide from one poleto the other in 1/120 second and make a completerevolution in 1/60 second, which would be at the rate of3600 rpm. If the compass needle is replaced by an ironrotor wound with copper bar conductors (usually

27

Figure 37. Shaded pole motor stator windings.

called a squirrel-cage rotor because the conductorsresemble a squirrel cage, as shown in figure 36, asecondary voltage is induced in the conductors by mutualinduction much in the manner that the secondary voltageis developed in a transformer.

7-13. Current flowing in the conductors produces amagnetic field which reacts on the rotating magnetic fieldand causes a rotation of the iron core similar to therotation of the magnetic needle. The direction ofrotation may be reversed by reversing the connections ofone phase.

7-14. Shaded-pole motor. The stator windings of ashaded-pole motor differ from other single-phase motorsby definitely projecting field poles (fig. 37). A low-resistance, short-circuited winding or copper band isplaced across one tip of each pole, from which the name“shaded-pole” is derived. As the current increases in thestator winding, the flux increases. A portion of this fluxcuts and induces a current in the shaded winding. Thiscurrent sets up a flux which opposes the flux inducingthe current; therefore, most of the flux passes throughthe unshaded portion of the pole, as shown in figure 38.

Figure 38. Flux path in a shaded-pole motor.

When the current in the winding and the main field fluxreaches a maximum, the rate of change is zero, so noelectromotive force is induced in the shaded winding. Alittle later the shaded winding current, which lags theinduced electromotive force, reaches zero, and there is noopposing flux. Therefore the main field flux passesthrough the shaded portion of the field pole. This resultsin a weak rotating magnetic field with sufficient torque tostart small motors. Because of the low starting torque,shaded-pole motors are furnished in ratings up toapproximately 1/25 horsepower and are used with smallfans, timing relays, small motion picture projectors, andvarious control devices. Shaded-pole motors are designedfor a specific direction of rotation that cannot be changedafter the motor is assembled.

7-15. Split-phase motor. Split-phase motors containtwo windings, the main winding and the starting winding.The main winding is wound on the stator and thestarting winding is wound on top of the main winding insuch a

Figure 39. Schematic of a single-phase, split-phase motor.

manner that the centers of the poles of the two windingsare displaced by 90°. The windings are connected inparallel (fig. 39) to the same supply voltage; therefore, thesame voltage is applied to both winding. The startingwinding is usually wound with fewer turns of small sizewire and has iron on only two sides. It, therefore, hasless inductance than the main winding, which has a lowresistance and is surrounded by iron on all sides exceptone. When the same voltage is applied to both windings,the current in the main winding lags the voltage morethan the current in the starting winding. This produces arotating field which starts the motor. As the motorapproaches full speed, a centrifugal mechanism mountedon the rotor opens a centrifugal switch (fig. 39) anddisconnects the starting winding from the line. If thecentrifugal mechanism should fail to open the switch, themotor will run hot because of the high resistance of thestarting winding and will burn

28

Figure 40. Schematic of a single-phase permanent-splitcapacitor motor.

out the starting winding if allowed to run any length oftime. This is the most frequent cause for failure of split-phase motors. The split-phase motors are usuallyfurnished in ratings from 1/60 to 1/3 horsepower and aredesirable for use in machine tools, office equipment,pumps, fans, blowers, oil burners, kitchen appliances, andlaundry equipment. Split-phase motors may or may nothave a built-in thermal overload relay for the protectionof the motor during an overload. The relay is usually ofthe automatic type, opening when the current in thewindings is above normal and automatically resettingwhen the current is restored to normal. To reverse thesplit-phase motor, reverse the loads of either the startingwinding or the running winding.

7-16. Capacitor-start motor. The capacitor-start

motor is so called because a capacitor instead ofresistance is used to split the phase. The capacitor,usually mounted on top of the motor, is connected inseries with the starting winding to provide the necessaryshift in time phase of the current flowing through it.This capacitor is usually intermittently rated and must bedisconnected for normal operation, which disconnectionis usually done by a centrifugal mechanism mounted onthe rotor. When the motor is stopped, the switch closesand is in the correct position when the motor is startedagain. The capacitor-type motor has a higher startingtorque at less current than the split-phase motor and alsoprovides a greater thermal capacity. Capacitor-startmotors are usually furnished in ratings from 1/6 to 1horsepower and are used on compressors, pumps, fans,and machine tools.

7-17. Permanent-split capacitor motor. Thepermanent-split capacitor motor is similar to thecapacitor-start motor, except that the permanent capacitor(fig. 40) is connected in series with the starting windingpermanently and is not removed from the circuit duringoperation by a centrifugal switch. This eliminates theneed for a centrifugal switch and switch mechanism.The capacitor is continuously rated and is selected to givebest operation at full speed while sacrificing startingtorque. Permanent-split-capacitor motors develop 40 to60 percent starting torque and are used on easily startedloads such fans and blowers.

7-18. Capacitor-run motor. The capacitor-run motorhas two capacitors connected in parallel (fig. 41). One, arunning capacitor, is a continuously rated capacitor andremains in the

Figure 41. Schematic of a single-phase dual voltage capacitor run motor.

29

Figure 42. Three-phase induction motor.

30

circuit while the motor is running. The other, a startingcapacitor, is intermittently rated and is used in the circuitduring starting. The starting capacitor is removed by acentrifugal mechanism and switch as the motorapproaches full speed. Therefore the capacitor-run motoris a combination of the capacitor-start and thepermanent-split capacitor motors. This motor has a highstarting torque as well as good running characteristics andis generally furnished in ratings of 1/2 horsepower andlarger. Capacitor motors may be reversed by changingthe leads to the starting winding at the motor terminals.

7-19. Three-Phase AC Induction Motors. Thethree-phase ac induction motor is also called a squirrel-cage motor. The rotating magnetic field of the three-phase motor operates the same as a two-phase motor.The difference between a two-phase and a three-phasemotor in the windings. The two-phase windings areplaced 90° apart where the three-phase windings areplaced 120° apart. This means that the currents thatproduce the magnetic field reach a maximum 1/180second apart in a 60-cycle circuit.

7-20. Notice figure 42, which shows the connectionof a wye-connected stator in a three-phase inductionmotor. The rotor of the motor is represented by thecompass needle, which points in the direction of themagnetic field and revolves as the magnetic fieldrevolves. The individual current waves are shown alongthe phase wires as they would actually be duringoperation. Notice the current in phase A reaches amaximum at position 1 and at that instant the currents inphases B and C are both negative.

7-21. At position 2, 1/180 second later, the currentis at a maximum in phase B and is negative in phases Aand C. At position 3, which is 1/180 second later than

position 2, the current is at positive maximum in phase Cand is negative in phases A and B. In the diagrams themagnetic field caused by the maximum positive current isshown in heavy dark lines. The other poles are indicatedwith dotted lines. The rotor, like the single-phase motor,follows the rotating magnetic field of the stator winding.

7-22. The speed of the induction motor is alwaysless than the speed of the rotating field of the stator. Ifthe rotor were to turn at the same speed as the rotatingfield, the rotor conductors would not be cut by anymagnetic field and no voltage would be induced in them.No current would flow; thus there would be no magneticfield in the rotor and, hence, no torque.

7-23. A three-phase induction motor exerts a torquewhen at rest and therefore starts itself when the propervoltage is applied to the stator field coil. To reverse thedirection of rotation of a three-phase motor, reverse theleads of any two phases.

7-24. The three-phase spring (wound rotor)induction motor is wound with a three-phase drumwinding. The windings are connected wye (y) or delta(wye connection is shown in fig. 43), and the three leadsare brought out and connected to three electrical contactrings (sliprings) which are secured to the shaft. Brushesriding on the rings are connected to an external resistancethrough which the rotor circuit is completed. Motorscontaining wound rotors have a high starting torque withlow starting current us adjustable speed.

7-25. Synchronous Motors. Synchronous motorsare divided into two classes according to their size andapplication. The larger horsepower motors use three-phase power and have separately excited salient polerotors. The smaller motors are usually furnished asfractional-horse-

Figure 43. Schematic of a three-phase slipring induction motor.

31

Figure 44. Schematic wiring diagrams of universalmotors.

power motors and obtain their rotor-excitation currentthrough induction. Although an induction motor isconsidered as a constant-speed motor, it is subject toapproximately 10 percent variation in speed under variousload conditions, since the operating torque depends uponthe percentage of slip between the rotating magneticpoles and the magnetic flux of the rotor. The speed of asynchronous motor is controlled by the frequency of thealternating-current power source and is, therefore,maintained with a high degree of accuracy. The smaller

size synchronous motors are constructed as reluctancemotors or hysteresis motors, which are described infollowing paragraphs.

7.26. Reluctance motor. The stator of a reluctancemotor is similar in construction to that of the single-phase induction motor and may be of the shaded-pole,split-phase, or capacitor type. The squirrel-cage rotorshave grooves cut to allow the addition of salient poles.The number of salient poles mounted on the rotorcorresponds to the number of rotating stator poles. Themotor starts as an induction motor, but, upon reaching aspeed near synchronism, it pulls into step because of thesalient poles and operates at exactly synchronous speed.The reluctance motor, unlike the larger size synchronousmotor (which has on the rotor a field winding suppliedwith direct-current excitation and which operates at unityor at a leading power factor with high efficiency),operates at a lagging power factor and has a rather lowefficiency. Therefore, the reluctance motor is used onlywhere exact synchronous speed is required, such as inelectric clocks, time switches, relays, and meters.

7-27. Hysteresis motor. The construction of thehysteresis motor is similar to that of the reluctance motorexcept for the rotor. The rotor does not have a squirrel-cage winding. Instead the rotor core is usually made of aring of metal having permeability, such as chrome orcobalt steel. The highly magnetic core material retains itsmagnetism over a period of time and this enables therotor to reach its synchronous speed. Hysteresis motorsdevelop a constant torque from zero synchronous speedand are used in a clock’s timing devices; they will operateunattended for long periods of time.

7-28 Universal Motors. Universal motors aredesigned for operation from either direct current orsingle-phase alternating current and are all of the series-wound type; that is, the field windings are connected inseries with the armature windings. Universal motors aredivided into two types: the straight series-wound universalmotor and the compensated series-wound universalmotor.

7-29. Straight series-wound universal motor. Thestraight series-wound universal motor has the fieldwindings connected in series for opposite polarity, thesame as the field winding of any direct-current motor,and then in series with the armature (fig. 44A). Thistype motor uses salient-type pole pieces (fig. 45) formounting the field windings and is usually furnished insizes up to 1/3 horsepower but can be furnished in largersizes for special applications. The motor full speed israted from 1800 rpm on the larger sizes to 5000 rpm onthe smaller sizes and no-load speeds ranging from 12,000to 18,000 rpm. Since these motors run at dangerouslyhigh speeds at no-load, they are usually built into the

32

Figure 45. Salient pole laminated steel core of a universalmotor.

equipment being driven. This type motor is used inportable machines and portable equipment in general.

7-30. Compensated series-wound universal motor. Thecompensated series-wound, distributed-field, universalmotor contains a main winding and a compensatingwinding connected in series with the armature (fig. 44B).The core of this type motor is similar to the constructionof the core of a split-phase alternating-current motor (fig.46). The main winding is usually placed in the slots firstand the compensating winding is placed over it, 90electrical degrees away. The compensating windingreduces the reactance voltage present in the armaturewhen alternating current is used. It has a bettercommutation and power factor than does the straightseries-wound universal motor, and usually comes inhigher horsepower ratings. Compensated series-wounduniversal motors are used with portable tools, officemachines, vacuum-cleaning equipment, and portableequipment in general.

8. Motor Maintenance

8-1. Cleanliness is essential if we are to havetrouble-free motor operation. Dirt, moisture, andexcessive oil tend to restrict air circulation, deteriorate theinsulation, and accelerate wear and friction. To increasethe life of the motor, you should wipe all excessive dirt,oil, and grease from the surface of the motor. Use acloth moistened with a recommended cleaning solvent.

CAUTION: Do not use flammable or toxic solventsfor cleaning, as they may cause injury to personnel ordamage to property.

8-2. The inside of the motor can be cleaned with ablower or with compressed air. Care should be exercisedwhen using compressed air so the insulation is notdamaged by the blast of air.

8-3. Motor Lubrication. You must be sure themotor has been properly lubricated. Lubrication shouldbe done according to the applicable publication for themotor.

8-4. You should also make periodic checks forgrease or oil leakage and for overlubrication. Afterlubricating a motor, be sure to wipe away any excess oilor grease.

8-5. Wiring. The wiring leads to the motor must bekept clean and secure and checked for wear. If thewiring becomes frayed, it must be replaced.

8-6. Mounting. Motors must be kept secure toperform efficiently. A loose mounting can cause a belt toslip and wear or can cause vibrations which tend toharden any copper component (wiring and tubing).

9. Circuit Protective and Control Devices

9-1. Electricity, when properly controlled, is of vitalimportance to the operation of refrigeration equipment.When it is not properly controlled, however, it canbecome dangerous and destructive. It can destroycomponents or the complete unit; it can injure personneland even cause their death.

9-2. It is of the greatest importance, then, that wetake all precautions necessary to protect

Figure 46. Compensated series-wound universal motor.

33

the electrical circuits and units and that we keep thisforce under proper control at all times. In this sectionwe shall discuss some of the devices that have beendeveloped to protect and control electrical circuits.

9-3. Protective Devices. When a piece ofequipment is built, the greatest care is taken to insure thateach separate electrical circuit is fully insulated from allothers so the current in a circuit will follow its intendedindividual path. Once the equipment is put into service,however, there are many things that can happen to alterthe original circuitry. Some of these changes can causeserious troubles if they are not detected and corrected intime.

9-4. Perhaps the most serious trouble we can find ina circuit is a direct short. You have learned that the termis used to describe a situation in which some point in thecircuit, where full system voltage is present, comes indirect contact with the ground or negative side of thecircuit. This establishes for current flow a path thatcontains no resistance other than that in the wire carryingthe current, and these wires have very little resistance.

9-5. You will recall that, according to Ohm's law, ifthe resistance in a circuit is extremely small, the currentwill be extremely great. When a direct short occurs, thenthere will be an extremely heavy current flowing throughthe wires.

9-6. To protect electrical systems from damage andfailure caused by excessive current, several kinds ofprotective devices are installed in the systems. Fuses,circuit breakers, and thermal protectors are used for thispurpose.

9-7. Circuit protective devices, as the name implies,all have a common purpose: to protect the unit and thewires in the circuit. Some are designed primarily toprotect the wiring. These open the circuit in such a wayas to stop the current flow when the current becomegreater than the wires can safely carry. Other devicesprotect a unit in the circuit by stopping current flow to itwhen the unit becomes excessively warm.

9-8. Control Devices. The components in anelectrical circuit are not all intended to operatecontinuously or automatically. Most of them are meantto operate at certain times, under certain conditions, toperform very definite functions. There must be somemeans of controlling their operation. Either a switch or arelay, or both, may be included in the circuit for thispurpose.

9-9. Switches. Switches are used to control thecurrent flow in most electrical circuits. A switch is usedto start, to stop, or to change the direction of the currentflow in the circuit. The switch in each circuit must beable to carry the normal current of the circuit and mustbe insulated heavily enough for the voltage of the circuit.

9-10. The toggle switch (as shown in fig. 47 alongwith the knife switch which is used to simplify theoperation of a toggle switch) is used more than any otherkind of switch, but there are others, such as pushbutton,microswitch, rotary selector, and even relays andmagnetic motor starts, which can be classified as switchessince they operate, start, and stop current flow in acircuit.

9-11. Magnetic motor starters. A magnetic motorstarter is wired to satisfy a particular application; andthere are numerous applications, so we will not attemptto cover all of them. Figure 48 shows a pump, airconditioner, and fan operating through motor starters.Look at figure 48 and notice the two single-pole singlethrow (SPST) switches, thermostat, holding coils, motorprotectors, and step-down transformer. Also notice thatthree-phase equipment must have protective devices in atleast two wires, but single-phase equipment may beprotected by one protective device.

Figure 47. Various knife and toggle switches.

34

Figure 48. Use of magnetic motor starters.

9-12. In figure 48, the air conditioner will notoperate unless the fan and pump holding coils areenergized, and the thermostat switch is closed. Noticethat the control circuit for the air conditioner is wired inseries through the auxiliary contacts of the fan and pumpmotor starters. Also, notice that a low voltage may beused to control a higher voltage with the use of a step-down transformer.

9-13. If switches Nos. 1 and 2 are closed, the pumpand fan will operate but the air conditioner will not untilthe thermostat completes the circuit for its holding coil.If an overload develops in the pump or fan, the heatersopen the respective control circuit, which in turn breaksthe control circuit for the air conditioner.

9-14. Maintenance and Troubleshooting. Most ofthe troubles in motor starters will be in the load contacts,holding coil, or heaters. A voltmeter can be used to

check the load contacts, if the voltmeter leads areconnected in parallel to each set of contacts and theholding coil is energized. The voltmeter should readzero. If it does not, then the contacts need to be cleanedor replaced. With power off, the heaters and the holdingcoil may be checked with the ohmmeter. Heaters shouldbe sized correctly to give protection to the motor; ifundersized they would cause nuisance tripping in normalcurrent flow.

9-15. In this chapter you have studied thefundamentals of electricity, circuits, Ohm's law,transformers, magnetism, electrical meters, circuitprotective and control devices, and motors that are usedto drive refrigeration equipment. Let's continue withanother type of drive for refrigeration equipment, thegasoline engine.

35

REVIEW EXERCISES

These review exercises are intended to assist you in studying the material in this memorandum. The figures following eachquestion correspond to the paragraph numbers that contain information pertaining to the exercise. In order to obtain themost benefit from the review exercises you should try to work them before you look at the answers in the back of thememorandum. Do not send in your solutions to the review exercises.

CHAPTER 1

Objective: To show knowledge of the fundamentals of electricity, circuits, motors, circuit protectors, troubleshooting, andsafety.

1. What type of electricity does a generator produce? (1-4)

2. Define voltage, current, and resistance. (1-6, 10)

3. Why are alloys of nickel and chromium used in heater elements? (1-11)

4. The resistance of copper wire is determined by three things. What are they? (1-12)

36

5. What type metal is used to make a permanent magnet? (1-16)

6. What determines the output frequency of an ac generator? (2-10)

7. Given an electrical potential of 110 volts and a resistance of 55 ohms, find the amperage draw. (3-4)

8. Given a resistance of 12 ohms and a 20-amp current draw, find the electrical potential. (3-5)

9. Given a 5-amp current draw and an electrical potential of 110 volts, find the resistance in ohms. (3-6)

10. If a dc motor draws 1 ampere of current when connected to 746 volts, what is the horsepower of the motor? (3-25, 27)

11. What is the electrical symbol for inductance? (4-8)

37

12. What effect does a capacitor have on an ac motor circuit? (4-10; Fig. 17)

13. When will the apparent power be equal to the true power in an ac circuit? (4-12)

14. Will a transformer operate on any dc circuit? (5-1)

15. Name the three primary parts of a transformer. (5-2)

16. List the four types of transformer connections. (5-21)

17. What is the purpose of the various size resistors connected in series with the voltmeter movable coil? (6-3)

18. Why is a shunt connected in parallel with the ammeter meter circuit? (6-4)

19. When will maximum current flow through the ohmmeter circuit? (6-7)

38

20. Before using a dc meter on an ac circuit, what must be added to the circuit? (6-9)

21. What the purpose of the wattmeter? (6-10)

22. How would a voltmeter be connected to check or a blown fuse? (6-20)

23. What must be done to the circuit before making a continuity check in a parallel circuit? (6-30)

24. What determines the speed of rotation of an ac motor? (7-2)

25. How many windings must a single-phase induction motor have? (7-5)

26. What would happen to the split-phase motor if the start winding failed to disengage? (7-15)

27. Which of the single-phase motors has the best running characteristics and highest starting torque? (7-18)

39

28. How is a three-phase motor started? (7-23)

29. Why does a reluctance motor operate at exactly synchronous speed? (7-26)

30. What type motor may be used on either ac or dc? (7-28)

31. How often should a motor be lubricated? (8-3)

32. What are circuit protective devices used for? (9-7)

33. On three-phase equipment how many protective devices must be in the circuit? (9-11)

34. In figure 66 the air conditioner will not operate if the fan is not on. Why? (9-12)

35. Where will most of the troubles be located in a magnetic motor starter? (9-14)

40

CHAPTER 2

Fundamentals of Gasoline Engines

Occasionally you may be called upon to serviceengine-powered refrigeration units. You will find theseengine-powered units on refrigerated vans, mobile fieldunits, and some trailers used for electronic systemmaintenance.

2. Since you will be operating and servicing theseunits, you must possess a working knowledge of gasolineengine. Let's begin with a discussion of the four strokecycle engine.

10. Principles of Operation

10-1. For a four stroke cycle internal-combustionengine to operate and deliver power, the following seriesof events must occur in the order illustrated in figure 49.A mixture of fuel and air must enter the cylinder and becompressed. The mixture must be ignited by somemeans, causing it to burn and expand. The expandinggases then force the piston down. The piston then mustmove upward, expelling the burned gases from thecylinder. This series of five events must take place timeand time again in exactly the same sequence if the engineis to deliver power. To improve the efficiency of theengine, various valves are timed to open or close at apiston position slightly before or slightly after a dead-center position.

10-2. The two stroke cycle engine is a one thatcompletes its cycle of operation in only two strokes,instead of four as in the four stroke cycle. Mechanicallythe two stroke cycle engine is slightly different. Somehave the intake and exhaust ports placed in the cylinderwall, while others may use a combination of intake portsand mechanically operated exhaust valves in thecombustion chamber. When ports are used and thepiston moves down on its power stroke, it first uncoversthe exhaust port to allow burned gases to escape and thenuncovers the intake port to allow a new air-fuel mixtureto enter the combustion chamber. On the upward stroke,the piston covers both ports and at the same timecompresses the new mixture in preparation for ignitionand another per stroke.

10-3. Theoretically the two stroke cycle engineshould produce twice as much power as a four strokecycle engine of the same size. This is not true, becausefuel is wasted and power is lost when some of theincoming fuel mixture mixes with the exhaust gases andis exhausted out of the engine. In this manner thevolumetric efficiency of the engine is reducedconsiderably. Volumetric efficiency is the ability of anengine to take in enough air to insure completecombustion. However, a two stroke cycle produces morepower output per unit weight than a four stroke cycleengine.

10-4. So far all we've discussed is the operation ofgasoline engines. Now we will over the servicing ofgasoline engines. We will start with the lubricationsystem.

11. Maintenance of Lubrication System

11-1. The lubricating system of an engine includes anumber of different units. In this system the oil ispicked up from the oil pan reservoir by the pump. Thepump is usually driven by the camshaft. An oil strainer isplaced in series with the pump to remove foreignsubstances, such as metal particles, dirt, etc, from the oil.The oil is forced through metal tube and galleries in theengine block to various parts of the engine. It is theneither splashed or forced on the moving parts of theengine after which the oil returns to the oil pan reservoir,thus completing the cycle.

11-2. In order for the lubrication system to functionproperly, the operator must observe and record the oilpressure at predetermined intervals, maintain the properoil level in the crankcase of the engine, and change theoil and oil filter element, as specified by the technicalmanual applicable to the specific engine.

11-3. Oil Pressure Gage. The oil pressure gageindicates the resistance of the oil being circulated throughthe engine. The resistance is generally

41

Figure 49. Four stroke five event cycle principle.

measured in pounds per square inch. A pressure gagedoes not show how much oil there is in the crankcase. Itmerely shows that oil is being pumped sufficiently tocreate an indicated pressure. If the oil pressure gage doesnot show any oil pressure, the engine must be stopped,since it is an indication that the oil is not circulating andlubricating the moving parts. The engine will be severelydamaged if it is allowed to operate without oil pressurefor a short length of time.

11-4. Oil Level Gage. The oil level gage rod isusually of the bayonet type, similar to that used onautomobiles, and is used to check the oil level in thecrankcase. The gage rod is usually stamped at “add oil”and “full” levels. Oil level on the bayonet gage rodshould be taken only when the engine is not operatingand the engine oil is at normal operating temperature.Always keep the oil above the “add” mark.

11-5. Oil Filter. The primary function of the oilfilter is to filter out contaminating substances as the oilpasses through the filtering element. Two types of oilfilters are used: one is the sealed element type and theother is the replaceable element type.

11-6. Most oil filters are designed with a bypassvalve which permits free circulation of the lubricating oilf the filter element becomes clogged. Normally a filterelement should be changed when the lubricating oil inthe engine is changed. This change should be performedat such intervals as recommended by the applicablepublications.

11-7. Use care when replacing the filter - to avoiddamaging the oil lines or the oil line fittings. Our nextdiscussion will be the maintenance of the fuel system.

12. Maintenance of Fuel System

12-1. A gasoline engine fuel system consistessentially of a storage tank for the fuel, a fuel filter toclean the fuel, a fuel pump to transfer the fuel from thetank to the carburetor, and a carburetor to mix the fuelwith the air.

12-2. Fuel Filter. Fuel filters may be of variousdesigns and located at any point between the fuel tankand the carburetor. In figure 50 the fuel enters the bowland pass up through the filter screen before it flows outthrough the outlet. Water, or any solid caught by thescreen, settles to the bottom of the bowl. The bowl canbe removed and cleaned.

12-3. Fuel Pump. The fuel pump pumps gasolinefrom the fuel tank, through the fuel filter, to thecarburetor float chamber, at approximately 3 psi.

12-4. Carburetor. The basic function of thecarburetor is to meter the air and fuel in varyingpercentages according to the engine requirements. Themost desired mixture has an air-fuel ratio of 15 to 1-15parts of air to 1 part of fuel by weight. A 15 to 1 ratio isreferred to as a normal or medium mixture. A mixturecon-

42

Figure 50. Fuel filter.

taining less air is known as a rich mixture. Maximumhorsepower is obtained at a ratio of 12 or 13 to 1;maximum economy, however, is obtained with a 15 to 1ratio. The carburetor must automatically vary theproportion of air and fuel to meet the changingconditions under which the engine operates.

12-5. To procure maximum horsepower andmaximum economy from an engine, it is sometimesnecessary to make certain carburetor adjustment. The

Figure 51. Carburetor.

carburetor shown in figure 51 is one used with a smallair-cooled engine which operates a 25-cubic footrefrigerator. This carburetor has three adjustments: themain needle valve, the idle adjusting screw, and thethrottle adjusting screw. The main needle valve metersgasoline to the engine at operating speeds, the idleadjusting screw meters gasoline to the engine at idlespeed, while the throttle adjusting screw adjusts the idlingspeed of the engine. Most carburetors have only thelatter two adjustments. In these carburetors the gasolineis metered to the engine automatically.

12-6. Air Cleaner. The carburetor air cleaner mustbe kept clean to prolong engine life. Two types of aircleaners are used. They are the wet and dry types. Atcertain intervals, as recommended by the applicablepublication, the wet filter is disassembled, washed innonflammable cleaning solvent, reassembled, and refilledor sprayed with oil. Dry type cleaners are replaced at

Figure 52. Ignition system.

prescribed interval. They must never be oiled; however,in emergencies they may be cleaned with compressed air.

12-7. We've mentioned previously that the fuel-airmixture must be ignited by an electric spark from a sparkplug; let's discuss the system that causes this function.

13. Maintenance of Ignition System

13-1. The complete function of the ignition systemis shown in figure 52, but let's discuss each oneseparately.

13-2. Spark Plugs. Spark plugs should be removed,cleaned, and inspected at intervals prescribed by themanual for the particular engine. This operation isimportant because dirty spark

43

Figure 53. Adjusting spark plug gap.

plugs and plugs that have insufficient or too large a gapbetween the electrodes will cause hard starting andirregular firing of the engine.

13-3. Using a thickness gage, as shown in figure 53,adjust the gap between the electrodes to the specifiedamount recommended by the manual for the particularengine. The electrodes are spaced properly when thecorrect thickness gage can be lightly drawn betweenthem.

13.4. The coil (transformer) is used to step up thevoltage to approximately 18,000 volts dc. To do this theprimary of the coil is connected to a set of points. Thesepoints open and close to create pulsating dc that can bestepped up. The secondary side of the coil which alsoproduces pulsating dc is connected to the rotor in thedistributor and from there to each spark in turn.

13-5. The condenser (capacitor) is in the circuit tohelp collapse the magnetic field and reduce arcing at thepoints.

13-6. Distributor. The distributor with itscomponents is shown in figure 54. The distributor pointsshould be inspected periodically. To inspect the conditionof the point, stop the engine and remove the distributorcap and rotor. Then examine the distributor breakerpoints for pits or evidence of overheating. If the pointsare badly pitted or burned, they should be replaced.

13-7. After the points are replaced, adjust theclearance when fully open as prescribed by thepublication for the specific engine. Also, replace therotor and cap.

13-8. Storage Battery. The storage battery is a veryvital part of the electrical and ignition system and mustbe properly maintained for dependable automaticoperation.

13-9. The most common type of storage battery isthe lead and acid type. It is so called because the plates

are composed of lead and the electrolyte is a solution ofacid.

13-10. A battery must be tested periodically todetermine its state of charge. To test the specific gravityof the electrolyte of each cell, remove the filler caps,being careful to prevent dirt or foreign matter fromfalling into the cells.

13-11. Use a hydrometer to test the specific gravityof each cell. If the specific gravity is less than 1.175,increase the generator charging rate, or recharge thebattery.

13-12. If the unit is being operated in a tropical orhot climate and the specific gravity is over 1.225, thecharging rate should be reduced. If the unit is operatingin a temperate climate, the charging rate should not bereduced unless the specific gravity is over 1.290. Whenoperating the unit in a frigid or cold climate, always keepthe battery fully charged.

13-13. The battery electrolyte level should beinspected daily. When available, distilled water should beused to refill a storage battery. If the water level is low,refill each cell so that the level is about one-half of aninch above the top of the plates. It is important that theelectrolyte level be properly maintained at all times. It isalso very important that the specific gravity be

Figure 54. Distributor.

44

maintained at sufficient strength to prevent freezing inextremely cold locations.

13-14. If the electrolyte level is too low to obtain areading with the hydrometer, refill the battery withdistilled water and allow the unit to operate for an houror more before taking a hydrometer reading; otherwise anaccurate, specific gravity test cannot be obtained.

13-15. Wash the battery terminals, cable clamps, andcables with a solution of water and soda. See that thevents in the filler caps are open. To keep the terminalsand battery cable clamps from corroding, coat them withgrease. Do not drop a battery, and don't pound on theterminal. At intervals, remove the battery from itscradle, clean the cradle, and coat it with rust preventivecompound.

13-16. Now that we have oil in the engine, fuel inthe tank, and voltage to the spark plug, we can start theengine. Wait, we've forgotten another important system- the cooling system. We must have a system that willkeep the engine at a normal temperature. We had betterdiscuss this topic a little further.

14. Maintenance of Cooling System

14-1. All internal combustion engines are equippedwith some type of cooling system to dissipate the greatamount of heat they generate during operation. Aboutone-third of the heat generated by combustion must bedissipated by the cooling system. Cooling systems areclassified into two categories - liquid cooling and aircooling.

14-2. Liquid Cooling. A simple liquid-coolingsystem consists of a radiator, a circulating pump, a fan, athermostat, and a system of water jackets and waterpassages within the engine.

14-3. If the engine temperature runs abnormallyhigh, clean the exterior of the radiator by blowingcompressed air through the fins to dislodge any foreignmaterial and dead insects. If the temperature still runshigh, heating may be due to an accumulation of sludge inthe radiator. It is then best to drain and flush theradiator and engine block with dear water. Refill theradiator with soft water if it is available. If treated wateris not available, then use clear tap water, but drain andflush the system more often.

14-4. For operation below freezing or if the engineshould be standing idle at temperatures below freezingwithout being drained, ethylene glycol or a similarantifreeze should be added in sufficient quantity toprevent freezing at the lowest anticipated temperature.

14-5. Air Cooling. Air-cooled engines are designedin such a manner that the engine cylinder and head are

cooled by forced circulation of air provided by vanes onthe flywheel. The blower case inclosing the flywheel andthe baffles around the cylinder control the flow of air.Keep the system clean to prevent overheating of theengine and to assure uniform air velocity for propercooling. When the flywheel vanes, cylinder, and cylinderfins become coated with dust and dirt, the engine blowercase must be removed to clean the units. Using a stiffbristle brush or a scraper, remove all traces of dirt fromthe flywheel vanes and the cylinder and cylinder head fin.When maintaining cylinder fins it is important that finsnot become bent or otherwise damaged, as this will resultin hot spots within the cylinder.

14-6. Well, we've got the engine running normally;now we'll connect it to the compressor and get somework done.

15. Maintenance of Drive Mechanism

15-1. All drive belts should be examined regularlyfor wear, breaks, and adjustments. A worn belt becomesbright and smooth and tends to ride the bottom of thepulley or to slip when under a load. Continuous rubbingof the side of a belt wears down the edges and decreasesthe efficiency of its drive. Excessive friction from thecontact with abrasive dust causes internal breakdown of arubber belt. The presence of stray lubrication near arubber belt should be checked. Oil and grease soften anddeteriorate rubber. However, some flexible V-belts aremade of a special composition which is not affected bygrease or oil.

15-2. A belt which runs loose may snap in two.Low belt tension causes reduced and unsteady output.Unusual tautness brings on rapid wear of the belt, motorbearing, and compressor bearings.

15-3. If a belt shows indications of wear and cracks,it should be replaced. Always replace belts in matchedsets if at al possible. To check the tension of the drivebelt, which operates small compressor units, deflect thebelt at a point halfway between the engine pulley and thecompressor pulley. The deflection at this point, with a10-pound pressure, should be between 1/2 inch and 3/4inch. Adjust the belt as required or replace with a newone of the correct size. During the inspection andmaintenance of V-type belts it must be remembered thatthe driving force is on the sides of the pulley and not onthe bottom of the pulley groove.

15-4. The -four stroke cycle engine is most commonto the career field. The operation of the engine dependsupon proper maintenance. Each subsystem - fuel,electrical, and cooling - must work in harmony for peakperformance. We've

45

discussed the maintenance to be performed on eachsystem. The most important service that can be given anengine is proper lubrication. A large percentage ofpowerplant breakdowns are a direct cause of insufficientlubrication. Lubricate each powerplant according to therecommendations prescribed by the applicable

publications. The frequency of maintenance is outlinedin publications furnished by the manufacturers of theengines or by the TO when available.

15-5. Since we have covered the prime movers forrefrigeration equipment, let’s study the physics ofrefrigeration so the prime movers can be put to use.

46

CHAPTER 2

Practice Exercises

Objective: To show knowledge of the fundamentals and maintenance of the gasoline engine.

1. List the series of five events a four stroke cycle engine must go through to delivery power. (10-1)

2. When should the engine oil be checked? (11-4)

3. To obtain maximum economy what should the air-fuel ratio be? (12-4)

4. What type of electrical power is delivered to the ignition coil? (13-4)

5. What is the purpose of the condenser in the engine ignition circuit? (13-5)

6. What is the most common storage battery composed of? (13-9)

7. When should ethylene glycol be used? (14-4)

8. What is the best way to check a drive belt for correct tension? (15-3)

47

CHAPTER 3

Physics of Refrigeration

When venturing into the field of refrigeration, thefirst thing to learn is what goes on within the unit toproduce the “cold.” When we talk about somethingbeing “cold” we simply mean that it has less heat inrelation to something else. Every substance will havesome heat until the substance reaches absolute zero.

2. Heat is not destroyed in producing the cold but issimply removed from the place where it is unwanted.Heat is also in a mechanical refrigeration system to helpremove the unwanted heat.

3. The particular phase of natural science withwhich we are concerned involve the study of conditionsunder which certain changes take place; for example,when a solid melts or when a liquid boils.

16. Thermodynamics

16-1. Before we go into the study ofthermodynamics let's see what it means.“Thermodynamics is the physics that deals with themechanical action or relations of heat processes andphenomena.” One of the laws of thermodynamics is aformula which states that 778 foot pounds of work isequivalent to the heat energy of one Btu. Anther law is astatement that heat will only transfer from a highertemperature to a lower temperature.

16-2. Heat. All substances have heat; however,some will have more heat than others. Heat is themovement of the molecules within the substances. Themore they move the hotter the substance becomes. Tocompletely stop this movement the substance must bereduced in temperature to absolute zero.

16-3. Cold. We use this term to show that anobject has less heat than something else. Cold is notproduced but is merely a result of removing heat, whichremoval slows down the molecular movement. Manysubstances change their state from a solid to a liquid, agas or vice versa, with the addition or subtraction of heat.Other substances change their state by sublimation; inother

words, they change from a solid directly into a gas.There are different types of heat and different methodsof transferring this heat; but first let's look at some typesof heat.

16-4. Sensible Heat. Sensible heat is the amountof heat that can be added to or subtracted from asubstance without changing its state. Sensible heat canbe measured by a thermometer and detected by the bodysenses when present in appreciable amounts.

16-5. Latent Heat. Latent heat is hidden heatpresent in a substance. When ice at 32° F. melts intowater at 32° F., a change of state takes place. During thischange, a certain amount of heat is required to melt theice to water at 32° F. This heat which causes the changeof state is known as the latent heat of fusion. Now if thewater at normal atmospheric pressure is heated until itreaches 212°, it will not rise above the temperature untilit is all changed into steam (vapor). The heat thatchanges a substance from a liquid to a vapor is known asthe latent heat of vaporization.

16-6. The graph shown in figure 55 indicates thatthe amount of heat required to change 1 pound of waterfrom a solid to a liquid is 144 Btus. To change 1 poundof water from a liquid to a gaseous state requires a totalof 970 Btus.

16-7. Specific Heat. The fact that it takes 1 Btu toraise the temperature of 1 pound of water 1° does notmean that this is true for all substances. Somesubstances require more heat while others call for lessheat to raise their temperature equal amounts. Water isused for comparison, and the amount of heat required ascompared to water is the specific heat of a substance. Afew specific heat values are given for different substancesin figure 56.

16-8. Heat Transfer. Heat can be transferred froma hot object to a cooler object until both are equal intemperature. Heat can be transferred by any one ofthree different methods - conduction, convection, andradiation - or by a combination of these same methods.

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Figure 55. The three states of water and the heatrequired to make change state atmospheric pressure.

16-9. Conduction. When heat is transmitted fromone part of a substance to another part of the samesubstance or from one substance to another in directcontact the process is termed “conduction.” To verifythese two statements by experiment, use a metal rod, asillustrated in figure 57, placing one end over a flame. Asthe heat is absorbed, the molecules become active, and ina short time the cooler portion of the metal rod becomeswarm. Metals are good conductors of heat; but othermaterials, such as glass or cork, aren't. Materials whichoffer resistance to the flow of heat are known asinsulators or poor conducts.

16-10. Convection. Convection will be clear to you ifyou will follow the flow of air as it is transmitted througha heating system. When air is heated, it expands andbecomes lighter because of the change in density. Coolerheavier air flows in under the warm air and forces itupward. Then, as the warm air becomes cooler it

Figure 56. Specific heat values.

Figure 57. Heat transfer by conduction.

contracts, becomes more dense (heavier), and falls backto its source, where it is heated again. Thus, a circulationof air is set up which continues as long as heat isprovided. Figure 58 shows how heat is transferred byconnection.

16-11. Radiation. Heat may be transmitted fromone place to another without the use of any materialcarrier. The best example of this method of transfer ofheat is found in the radiation of energy from the sun tothe earth. We know that the atmosphere of the earth isnegligible at a comparatively short height above the earthand that the rest of the more than 90 million miles up tothe place where the sun’s atmosphere begins is filled withlittle or nothing. Therefore we know that both light andheat energy from the sun must come through space.Such a method of transfer is called radiation.

16-12. Radiation is the process of emitting radiantenergy in the form of rays or particles, as shown in figure59. In this case, a person's hand feels warm, eventhough it is a considerable distance from the source ofheat. The rays or particles pass through the air and heatthe hand more than the air between.

16-13. The transmission of heat by these threemediums can be controlled according to the requiredneeds. Conduction is aided-by providing

Figure 58. Heat transfer by convection.

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Figure 59. Heat transfer by radiation.

large conducting surfaces and good heat-conductingmaterials, such as iron, silver, or copper. Convection mybe assisted by speeding up the flow of air, as in a forced-air circulation system. The flow of heat can also becontrolled by dampers and thermostats according to one'sdesire. Dark colors usually absorb heat while light colorsreflect heat. For this reason, a certain surface finish mayradiate heat more efficiently than another. This is an aidto heating by radiation.

16-14. Temperature. The relative hotness of abody is termed “temperature.” This is not the quantity ofheat in the body substance, but merely its degree ofwarmth. An ordinary thermometer is used for themeasurement of temperature.

16-15. Two types of scales that are in general usefor temperature measurement are the centigrade and theFahrenheit. Figure 60 compare the two sales. Looking atthe centigrade scale, you can see that 0° is the freezingpoint and 100° the boiling point of water. There are 100divisions on the centigrade scale compared to 180 divisionon the Fahrenheit scale. Water freezes at the 32° pointand boils at the 212° point on the Fahrenheit scale.

Figure 60. Comparison of Fahrenheit and Centigradescales.

Figure 61. Density, volume, and weight.

16-16. It becomes necessary at times to convertfrom Fahrenheit to centigrade or from centigrade toFahrenheit temperatures. A simple formula forconverting these temperatures has been used by allmembers of the refrigeration trade. When convertingFahrenheit temperatures to centigrade, subtract 32° fromthe Fahrenheit temperature and multiply the remainderby .556 (5/9). To change centigrade temperatures toFahrenheit, multiply the centigrade temperature by 1.8(9/5) and add 32°. This formula should be memorizedfor use not only in the study of refrigeration but also inthe study of air conditioning.

16-17. Density. The density of a substance is theratio of its mass or weight to its volume. The upperportion of figure 61 shows that volume may be giveneither in liquid measure as gallons or in cubic measure ascubic inches. One gallon

Figure 62. Determining specific gravity.

50

of water has a weight of 8.337 pounds at a temperatureof 62° F.

16-18. The relative weight of liquids and solids isdetermined by specific gravity. Pure water is used as astandard reference with a value of 1. The specific gravityof cast iron may be figured by the method illustrated infigure 62. The weight of water which is displaced by a15-pound bar of cast iron is 2.1 pounds. Divide 2.1 into15 to get the specific gravity, which is about 7.1 for castiron. The specific gravity of a liquid may be measuredwith a hydrometer such as is used with a storage battery.The float in a hydrometer is calibrated so that the scalegives a direct reading of the specific gravity of the liquidbeing tested.

16-19. The density of a gas is expressed by specificvolume. The specific volume is the volume of 1 poundof the given gas under standard conditions (temperatureof 68° F. and pressure of 29.92 inches of mercury). Nextwe shall consider what is meant by pressure and some ofthe effects of it.

16-20. Pressure. Before a refrigeration can operatenormally, a pressure difference must exist betweendifferent units of the system. Consequently, pressure andits laws are important. Pressure is the force per unit ofarea expressed in pounds per square inch or pounds persquare foot. The pressure of air on one's body at sealevel is approximately 14.7 pounds per square inch, or2117 pounds per square foot. Since there are 144 squareinches in 1 square foot, 14.7 is multiplied by 144 to findthe pressure per square foot:

16-21. A material exerts pressure on its supportingsurface. For example, a desk (solid) exerts pressure onthe floor through its legs. If the legs were removed, thedesk would fall. A liquid, such as water in a pail, exerts

Figure 63. Types of pressure.

Figure 64. Illustration of horsepower.

pressure on the sides and bottom of its container. Agood illustration of gas pressure is the pressure exerted bythe substance used to inflate an ordinary balloon. Thegas pressure inflates the balloon, supporting all points ofits surface. Figure 63 illustrates the different types ofpressures explained in this paragraph. When you learnabout the refrigeration cycle, you will find thatmechanical power is used to increase pressure.

16-22. Work and Power. An understanding ofenergy relations is essential to a complete knowledge ofrefrigeration. Energy is “the capacity to do work,” andwhenever energy is spent there will be some work done.Work is “the force in pounds multiplied by the distancethrough which it acts.” The unit of work is called thefoot-pound. One foot-pound is the amount of work donein raising 1 pound vertically a distance of 1 foot.

16-23. Example. What amount of work is done inlifting 2000 pounds a distance of 10 feet?

Force X distance = work2000 X 10 = 20,000 foot-pounds

Power is the time rate of doing work. Mechanical poweris termed “horsepower.” One horsepower

Figure 65. Unit of heat content.

51

does work at the rate of 33,000 foot-pounds per minute.16-24. Referring to figure 64, you will see that if the

2000 pounds were lifted 10 feet in 2 minutes, the powerrequired would be:

16-25. Energy. In addition to mechanical power, weare concerned with electrical and heat energy. You willfind in refrigeration that changes in heat energy are thebasis of cooling. Electrical and mechanical energy arecombined in most systems to produce changes in heatenergy. The relationship between these three types ofenergy is expressed in terms of the following equivalents:

778 foot-pounds = 1 Btu1 horsepower = 2,545.6 Btus/hr1 horsepower = 746 watts

Figure 66. High and low side of system.

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16-26. Scientists have a theory that heat comes fromthe vibration of the molecules in a substance. The rateof vibration determines the temperature, while the totalenergy involved in the movement of all the molecules ofa substance determines the heat. Heat is measured inthermal units. The British thermal unit (Btu) is definedas the amount of heat required to raise the temperatureof 1 pound of water 1° F.

16-27. Looking at the example (see fig. 65), you cansee by the rise in temperature how 1 Btu was added tothe water, causing a change in its heat content. Notethat the state of the water does not change even thoughit has a higher temperature. Heat may be added withouta change of state until the boiling point of the water isreached.

16-28. Critical Temperature. We can liquefy anygas by lowering its temperature or by increasing thepressure. However, there are temperatures at which gasescannot be liquefied regardless of the applied pressure.These are called the critical temperatures.

16-29. Critical Pressure. The critical pressure of aliquid is the pressure at or above which the liquid willremain a liquid regardless of the applied heat.

16-30. Enthalpy. Enthalpy is the total heat(energy) in 1 pound of a substance. The enthalpy forwater is accepted at 32° F., where the accepted enthalpy

for refrigerants is at -40° F. Example: To find theenthalpy of 1 pound of 70° F. water, subtract 32° F. from70° F. Total heat at 70° F. = 38 Btu.

16-31. Entropy. Entropy is a mathematical constantthat is used by engineers for calculations of the energy ina system. Again, 32° F. and -40° F. are the acceptedbases used in these calculations. Most of the refrigerantperformance charts will show the constant entropy lines.

17. The Mechanical Refrigeration Cycle

17-1. Before studying the various changes whichtake place in the refrigeration cycle, it is necessary to seejust how latent heat and pressure changes have becomethe foundation of modern refrigeration.

17-2. Uses of Latent Heat. When ice melts, itsdegree of temperature remains constant; however, itabsorbs a large amount of heat in the process of changingfrom ice to water.

17-3. In the evaporator of the modern refrigerator,the refrigerant changes from a liquid to a gas. To makethis change of state, heat must be absorbed by therefrigerant. This heat can only come from the space tobe cooled. We can say that the cooling action within thecabinet takes place in the evaporator.

Figure 67. Compression system.

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Figure 68. Absorption system.

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17-4. The condenser is another area within therefrigeration cycle where latent heat of vaporization isused. The heat absorbed in the evaporator must be givenup in the condenser. The condenser is surrounded byeither air or water; and as the hot gas comes into contactwith either of these mediums, it gives up its heat andcondenses into a liquid.

17-5. You can see now that latent heat ofvaporization plays an important role within the cycle, butlet's not forget another important ingredient-pressuredifferences.

17-6. Utilization of Pressure Difference. Inrefrigeration, it is necessary to produce cold. This ismade possible when differences of pressure are present.The high and low sides of a system and places wherepressure varies during a cycle can be seen in figures 66and 67. The reduction of pressure within the cycle takesplace at the expansion valve. The refrigerant (of the R-12 type) boils at -21.7° F. under atmospheric pressure. Ifthe pressure is reduced to 11.999 psia, the boiling point islowered to -30° F. The cabinet temperature ismaintained above this temperature; therefore, the heat ofthe cabinet will be readily absorbed by the refrigerant.Now you should have an understanding of how pressuredifferences are used in obtaining the refrigeration effect.

17-7. Now that we've covered latent heat andpressure differences, we are ready to apply these to therefrigeration cycle.

17-8. The refrigeration cycle is common to allmachines made for towering of temperature in oureveryday living. The type of system used, however,depends upon the locality where the refrigeration isneeded.

17-9. Compression System. Figure 67 illustratesthe simplified refrigeration system. By applying thetheory of latent heat and pressure differences, you cansee what takes place in producing low temperatures. Thisillustration may be applied to any refrigerator regardlessof size or shape.

17-10. Every system involves a cycle of one kind oranother. We will trace through the entire cycle step bystep.

17-11. As the piston moves down, low-pressure gasis emitted through the valve to fill up the cylinder. Asthe piston starts up, compression takes place because thegas is forced into a smaller space. As the gas iscompressed, heat of compression is added. At thetopmost position of the piston, the gas is forced throughthe exhaust valve into the condenser The gas is at itshighest pressure. The condenser is a series of tubessurrounded by a cooling

medium (air or a water). As the gas is forced throughthe tubes, the heat of compression plus the latent heat ofvaporization from the evaporator is dissipated into thesurrounding cooling medium.

17-12. The removal of heat causes the gas tocondense to a high-pressure liquid. This liquid flows intoa receiver, which is merely a storage space for therefrigerant. The liquid leaves the receiver and moves upthe liquid line to the expansion valve, where the pressureof the liquid is reduced. As a result, it absorbs heatthrough the walls of the evaporator, lowering thetemperature of the compartment to be cooled. As theliquid boils, which is caused by the heat picked up fromthe cooling compartment, it changes into a low-pressuregas. This low-pressure gas now enters the suction lineleading to the compressor. The cycle is now complete.

17-13. Absorption System. The absorption systemdiffers from a compression system in that heat energy isused instead of mechanical energy to make a change inthe conditions necessary to complete a cycle ofrefrigeration. Gas, kerosene, or an electrical heatingelement is used as the source of heat supply.

17-14. To better explain the operation of theabsorption system, we have put figure 68 in block form.Also we have added a float in the condenser. Let's startthe cycle by creating a vacuum in the absorber andevaporator, and starting these pumps. Water will boil at40° F.-45° F. with a vacuum of 29.53 inches of mercury(Hg). As the refrigerant (water) is sprayed on the 55° F.chilled water coil, the refrigerant boils and absorbs theheat from the chilled water. The refrigerant vapor isthen absorbed by the lithium bromide, and becomesweaker. To have continuous operations, the lithiumbromide must be made stronger and the refrigerant mustreturn to the evaporator. To do this the generator pumpis started and a steam valve is opened. The generatorpump forces the weak solution through the heatexchanger (where the weak solution is preheated and thestrong solution from the generator is cooled), then intothe generator. Steam is used to make the refrigerant(water) go into a vapor again where it condenses intopure water in the condenser. As the refrigerant levelrises in the condenser the float opens to return therefrigerant into the evaporator for continuous operation.

17-15. We have discussed the physics ofrefrigeration and the cycle of the mechanical andabsorption refrigeration systems. Now let's discuss themedium used in these systems to transfer the heat fromwhere it is unwanted to a place where it isunobjectionable.

55

CHAPTER 3

Practice Exercises

Objective: To show knowledge of the physics of refrigeration and to apply the theory to the subtraction of heat.

1. At what temperature will all molecular movement stop? (16-2)

2. When a solid changes directly from a solid to a gas, what is it called? (16-3)

3. How is cold produced? (16-3)

4. Describe the term “sensible heat.” (16-4)

5. Describe the term “latent heat.” (16-5)

6. What is the specific heat of water? (16-7)

56

7. Convert -40° centigrade to Fahrenheit. (16-16)

8. How is the relative weight of liquids and solids determined? (16-18)

9. What is the pressure per square foot at sea level? (16-20)

10. What amount of work is done in lifting 33,000 pounds a distance of 2 feet in 1 minute? What the requiredhorsepower? (16-23, 24)

11. What is 1 Btu equal to in foot-pounds? (16-25)

12. How many Btus are required to raise the temperature of 50 pounds of water 2°? (16-26)

13. What is the temperature called at which a liquid cannot be liquefied regardless of the applied pressure? (16-28)

57

CHAPTER 4

Refrigerants

Heat cannot be transferred from the inside of therefrigerator to the outside without some sort of mediumor heat-carrying device. This medium is calledrefrigerant.

2. Just what is refrigerant? Well, the dictionarydefines it as follows, “A substance, such as ice, liquid air,ammonia, or carbon dioxide, used in refrigeration.” Wecould define refrigerant as the medium (fluid or gas) usedto transfer heat from the evaporator to the condenser.

3. The requirements for a refrigerant are almostself-explanatory. It is obvious that an automaticmechanism should be safe; that is, free from the dangerof poisonous, flammable, or explosive gases. Refrigerantsmust be noncorrosive in order that the more commonmetal can be used in the construction of the machinepart. It must also be such that its presence can be easilydetected and traced to its source in the event of leaks. Itis also desirable to keep pressures within the refrigerationcycle as close to atmospheric pressure as possible, for anygreat differences in pressures tend to cause leaks,overwork the compressor, and lower the overall efficiencyof the system. Another desirable characteristic of arefrigerant is stability. If a refrigerant is to have this,then it must remain chemically unchanged whileconstantly going from a low temperature to a hightemperature and back to a low temperature. It must notset up a chemical reaction with the lubricants used in thesystem. It must not chemically deteriorate if it comes incontact with air or moisture within the system.

4. There are various types of refrigerants used today.The choice depends upon the application. Eachmanufacturer attaches to his unit a nameplate whichgives the type and amount of charge in the system.Changing to a different refrigerant should not even beconsidered, since most units are deigned for use with onespecific refrigerant. Each refrigerant has a differentpressure-temperature relationship. This relationship willbe the topic of our next discussion.

18. Effect of Temperature and Pressure

18-1. As you learned earlier, we can liquefy any gasby lowering its temperature. At some temperatures thegas can be liquefied by increasing the pressure. However,there are temperatures at which gases cannot be liquefiedregardless of the applied pressure. These are calledcritical temperatures.

18-2. For example, we can change steam to water bylowering its temperature below 212° F. or raising thepressure; but at 689° F. no amount of pressure will effectthe change. Anyone living at a high altitude has noticedthat boiled food must be cooked for a longer period oftime or under pressure. Boiling temperatures of pointsare lower at lower atmospheric pressures and higher athigher atmospheric pressures. The critical pressure of agas (water vapor) is the minimum pressure required toliquefy (condense) it at its critical temperature.

18-3. The critical pressure of a refrigerant must beabove any condensing pressure that might be encounteredduring a cycle of operation; otherwise the high-pressuregas would not condense and the refrigeration machinewould cease functioning. If the ordinary condensingpressures are up near the critical pressure, the amount ofpower required to compress the refrigerant is excessive;therefore the critical pressure of a refrigerant must bewell above the normal condensing pressure.

18-4. If the critical temperature of a refrigerant isnot higher than the condensing temperature, the hot gascoming from the compressor will not condense regardlessof pressure. If the temperature differential is small,power consumption is excessive.

18-5. If the hot gas coming from the compressordoesn't cool, the refrigeration cycle is not complete. Theheat transferred to the refrigerant in the evaporatorcannot be dissipated at the condenser. What heat wastransferred in the evaporator? The heat from the foodand inclosed area.

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This caused the refrigerant to evaporate. Let's explainthis heat and vaporization process thoroughly.

18-6. Latent Heat of Vaporization. With theexception of the comparatively small amount of heatabsorbed by vapor superheated in the evaporator and inthat part of the suction line within the refrigerator space,all of the heat-absorbing or refrigerating capacity that arefrigerant has comes from its latent heat of vaporization.In other words it depends on how much heat therefrigerant requires per pound to be changed from aliquid to a gas. Everything else being equal, therefrigerant having the highest latent heat of vaporizationis the most desirable.

18-7. Boiling Point and Condensing Temperature.Each refrigerant is made up of a combination of chemicalelements. The various components of each differ inreaching their boiling point or the temperature at whichthey condense. The boiling point of a refrigerant is thattemperature and pressure at which it is changed from alow-pressure liquid to a low-pressure gas. The heatrequired comes from the area to be lowered intemperature. The evaporator is the heat-absorbingsection of a system. As stated before, the refrigerant R-12 has a boiling point of -21.7° F. at atmosphericpressure. This boiling point is well below the lowestevaporating temperature at which the system operates.

18-8. The critical temperature of a refrigerant isusually considerably higher than the condensingtemperature and pressure required in an operationalsystem. The critical temperature of R-12 is 233° F., andthe critical pressure s 582 pounds pr square inch. Thepressure temperature table for R-12, found in theappendix of this volume, will show the normal operatingpressure corresponding to a given temperature. (Table 2)

18-9. The cooling medium, such as air or water, iscooler than the refrigerant as it enters the condenser.Heat is absorbed by the cooling medium and dissipatedinto the atmosphere which changes the state of therefrigerant from a gas to a liquid.

18-10. Classification of Refrigerants. Today thereare a number of different refrigerants used bymanufacturers of refrigeration machines. The followingparagraphs are devoted to a discussion of a few differentrefrigerants, their characteristics, and the methods used intesting for leaks.

18-11. Ammonia (NH3). This refrigerant is usedmost in certain applications in industry and also in theabsorption type refrigerator. Ammonia is colorless andhas a pungent odor. It boils at -28°F. atmosphericpressure. When one volume of ammonia and twovolumes of air are mixed, there is danger of explosion.Ammonia very toxic and requires heavy fittings. Unitsusing ammonia must be water cooled. To detectammonia leaks, the repairman uses a sulphur candle, theflame of which gives off a white smoke when it comes incontact

with an ammonia vapor. Still another means of detectingan ammonia leak is the phenolphtalein paper method. A mild concentration of ammonia causes the paper to turnpink; heavier concentrations turn the paper scarlet.(Table 1)

8-12. Refrigerant (R-12). Refrigerant-12 is colorlessand odorless both as a liquid and as a gas. If a heavyconcentration of this gas is present, a very slight odor isevident, but the vapor will not irritate the skin, eyes,nose, or throat. R-12 boils at -21.7° under atmosphericpressure. The presence of moisture in R-12 does notcause corrosion; only a mild discoloration of brass, copperand steel results. It is noncombustible and also mixesreadily with oil. To detect R-12 and other halogenrefrigerant leaks the halide detector (as shown in fig. 69)may be used. Other methods may also be used.

Figure 69. Halide leak detector.

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18-13. Carbon dioxide. Carbon dioxide gas isharmless to breathe except, of course, in heavyconcentrations when all the oxygen is excluded. In suchcases, suffocation results. It has a slightly pungent odorand an acid taste.

18-14. Because of its low efficiency as compared toothers, this refrigerant is seldom used in householdrefrigerators. It is used principally in industrial systemsand on ships.

18-15. Other refrigerants. Other refrigerants used to agreat extent in the refrigeration industry try areRefrigerant-11, Refrigerant-22, and Refrigerant-11. Lesscommonly used refrigerants are Refrigerant-21,Refrigerant-113, butane, ethane, propane, and methylformate. (Tables 3-5)

18-16. You must become familiar with the safetyprecautions related to refrigerants, for as we'vementioned previously, working safely benefits both theequipment and you.

18-17. Transfer of Refrigerants. Refrigerants areobtainable in amounts from railroad carload to a 1-poundcan. However, most of the refrigerant is in 145-poundcylinders. These cylinders are too heavy for theserviceman to move from place to place so the refrigerantmust be transferred into smaller containers. This is doneby obtaining a small cylinder designed for the particulargas which is to be transferred. Connect a charging line,weigh the empty cylinder and cool it if possible (set in iceor other methods), invert the full cylinder, and open bothcylinder valves. Stop the transfer when the small cylinderbecomes 80-85 percent liquid full. CAUTION: Never filla cylinder over 85 percent liquid full and always wearprotective equipment when transferring refrigerant.

18-18. Let’s look at some of the “do's” and “don'ts”while handling refrigerant cylinders.

(1) Never drop cylinders or permit them to strikeeach other violently.

(2) Never use a lifting magnet or a sling whenhandling cylinders. A crane may be used when a safecradle or platform provided to hold the cylinders.

(3) Cylinder valve caps should be kept on at alltimes except when the cylinders are in use.

(4) Never fill a refrigerant cylinder completely fullof refrigerant. The safe limit is 85 percent full.Overfilled cylinders are apt to burst from hydrostaticpressure.

(5) Never mix gases in a cylinder.(6) Cylinders are made to hold gas - don't use

them for a support or roller.(7) Never tamper with the safety device on a

cylinder.(8) Open cylinder valves slowly and use a

cylinder valve wrench. Never use a monkey or Stillsonwrench for this purpose.

(9) Never force misfitting connections; make surethat the threads of regulators and unions are the same asthose on the cylinder outlet.

(10) Never attempt to repair or alter a cylinder orvalves.

(11) Never store cylinders near flammables.(12) Always keep cylinders in a cool place away

from direct sun rays if possible and fully secured in place.(13) Do not store full and empty refrigerant

cylinders together. They should be stored in differentsections of the shop to avoid confusion.

(14) Always insure that gas cylinders are securedin place both when empty and filled.

18-19. As we stated before, you should always wearprotective equipment while charging or transferringrefrigerant. However, if something happens when you donot have the protective equipment on and the refrigerantcomes in contact with your eyes or skin, you shouldknow the first aid that will help you. If the refrigerantcomes in contact with the eyes they can be bathed in a 2-percent boric acid solution. For frostbite on the skin thearea can be bathed with cold water and massaged aroundthe area until circulation is restored. Do not disturb thefrost blisters.

18-20. A refrigerant is the carrier of heat in asystem; consequently, it is found in different parts of thesystem in different states. How do we know which statethe refrigerant i in within the system? Very easy; we usethe refrigerant table. Using the table, we can check thepressures within the system and convert the pressures totemperatures. This can also tell us if the system is safeto open. Remember, even though you know a little firstaid, it's better to be safe than sorry.

18-21. Tables have been compiled throughexperiment and research for each of the most commonlyused refrigerants. These tables show the pressure,density, volume, heat content, and latent heatcorresponding to certain temperatures. The charts are sodesigned that when you have one condition given youcan determine the other relative factors. (Tables 1-6)

18-22. We have had a discussion on a few of themost important refrigerants and their purpose as heatcarriers in a refrigeration system. A refrigerant is thebloodstream of any refrigerator; it removes heat at a lowpressure as it evaporates, and gives up heat at a highpressure as it condenses. The properties of a few of themost common refrigerant gases are discussed and thecharacteristics noted, as well as the safety precautionswhich are essential and must be observed. You are theone who will be handling refrigerant, so don't be careless,for they can

60

cause personal injury. The sections covering safetyprecautions, safe handling of gases, and first aidtreatment list the “dos” and “don'ts” to be followed whendealing with refrigerants. Read and heed; these are foryour own

benefit. Tables which will be used in every step of thiscourse are contained in the appendix to thismemorandum.

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CHAPTER 4

Practice Exercise

Objective: To show knowledge of the characteristic of refrigerants and of safety practices in handling these refrigerants.

1. What is the critical temperature of water? (18-2)

2. Why must the critical pressure be above the condensing pressures? (18-3)

3. Which refrigerant would be the most desirable - one with the lowest or highest latent heat of vaporization? (18-6)

4. What kind of a refrigerant gives off a white smoke when a leak is detected while using a sulphur candle? (18-11)

5. What is the safe limit for filling a refrigerant cylinder? (18-17, 18)

6. If refrigerant comes in contact with the eyes, they may be bathed in what? (18-19)

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Glossary

ABSOLUTE HUMIDITY - The amount of moisture that is in the air; it is measured in grains per cubic foot.

ABSOLUTE PRESSURE - Gage pressure plus atmospheric pressure (see pressure conversion table).

ABSOLUTE TEMPERATURE - The temperature that is measured from absolute zero (-460° F., zero° R., and -273° C.,zero° K.)

ACCUMULATOR - A tank that is used to keep liquid refrigerant from flowing to the compressor.

ACTIVATED ALUMINA - A chemical desiccant.

ACTIVATED CARBON - Processed carbon that is used for a filter.

ADIABATIC COOLING - Process of changing sensible heat for latent heat without removing heat (evaporative cooling).

ANEMOMETER - An instrument used to measure the rate of airflow.

ATMOSPHERIC PRESSURE - Pressure that is exerted upon the earth by the atmospheric gases.

AUTOTRANSFER - Common turns serve both the primary and secondary coils. Different taps are used to step up or stepdown the voltage.

AZEOTROPIC REFRIGERANTS - These are mixtures of refrigerants that do not combine chemically but provide goodrefrigerant characteristics.

BACK PRESSURE - Low side pressure or suction pressure.

BOYLE’S LAW - The volume of a given mass of gas varies as the pressure varies if the temperature remains the same.

BRITISH THERMAL UNIT - The amount of heat required to raise the temperature of 1 pound of water 1° F.

CALORIE - The quantity of heat required to raise the temperature of 1 gram of water 1° C.

CASCADE SYSTEM - Refrigeration system where two or more systems are connected in series to produce ultra-lowtemperatures.

CHARLES’ LAW - The volume of a gas varies directly with the temperature provided that the pressure remains constant.

COEFFICIENT OF PERFORMANCE (COP) - The ratio of energy applied as compared to the energy used.

COMPOUND REFRIGERATION SYSTEM - A system with two or more compressors or cylinders in series.

CRITICAL PRESSURE - The pressure of the saturated vapor at the critical temperature.

CRITICAL TEMPERATURE - The temperature at which the liquid and vapor densities of a substance become equal.

CROSS CHARGED - Two different fluids used to create the desired pressure-temperature relationship.

CRYOGENIC FLUID - An ultra-low temperature gas or liquid.

CRYOGENICS - Refrigeration producing temperatures at or below -250° F.

CURRENT RELAY - A relay which makes or breaks a circuit depending on a change in current flow.

DALTON’S LAW - The total pressure of a mixture of gases is the sum of the partial pressures of each of the gases in themixture.

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DENSITY - The mass of a substance per unit volume (consistency).

DEWPOINT - The temperature at which a saturated vapor will begin to condense.

DRY ICE - Solid carbon dioxide at approximately -109° F.; it is used in the shipment of produce.

EBULATOR - A sharp-edged material inserted in a flooded evaporator for better efficiency.

FLASH GAS - When changing from a high-pressure liquid to a low-pressure liquid some of the liquid flashes (evaporates)off and cools the remaining liquid to the desired evaporation temperature.

FOOT-POUND - The amount of work done in lifting 1 pound 1 foot.

GRAIN - A unit of weight; 7000 grains equals 1 pound.

HEAD, STATIC - Pressure of a fluid measured in terms of height of the column of the fluid.

HEAT LOAD - The Btus that are removed in 24 hours.

HEAT OF COMPRESSION - The transformation of mechanical energy of pressure into energy of heat.

HYDROMETER - An instrument used to measure the specific gravity of a liquid.

HYGROMETER - An instrument used to measure the ratio of moisture in the air.

INDUCTION MOTOR - An ac motor that operates on the principles of a rotating magnetic field.

KATATHERMOMETER - An alcohol thermometer used to measure air velocities by means of cooling effect.

KELVIN SCALE (K) - A thermometer scale that is equal to centigrade but using zero as absolute zero instead of -273° C.(absolute centigrade).

LATENT HEAT - Hidden heat; heat energy that a substance absorbs while changing state.

MANOMETER - A U-shaped tube filled with a liquid that is used to measure the pressure of gases and vapors.

MEGOHM - One million ohms.

MULLION HEATER - An electrical heating element used to keep the stationary part (mullion) of the structure between thedoors from sweating or frosting.

MULTIPLE EVAPORATION SYSTEM - A system with two or more evaporators connected in parallel.

MULTIPLE SYSTEM - A system with two or more evaporators connected to one condensing unit.

OIL SEPARATOR - A device used to remove oil from a gaseous refrigerant.

OZONE - A gaseous form of oxygen, usually generated by a silent electrical discharge in ordinary air.

PITOT TUBE - Part of an instrument used to measure air velocities.

POTENTIAL ELECTRICAL - The electrical force which tries to move or moves the electrons in a circuit.

POTENTIAL RELAY - A relay which is operated by voltage changes in an electromagnet.

POWER FACTOR - Correction coefficient for ac power.

PYROMETER - A device used to measure high temperatures.

RANKIN SCALE (R) - A thermometer scale that is equal to Fahrenheit but using zero as absolute zero instead of -460° F.(absolute Fahrenheit).

RELATIVE HUMIDITY - The percent of moisture in the air as to what it can hold at that temperature and pressure.

SATURATION - When air is saturated it is holding the maximum amount of water vapor at that temperature and pressure.(It may also be applied to other substances.)

SENSIBLE HEAT - Heat that can be measured and causes a change in temperature.

SOLAR HEAT - Heat energy waves of the sun.

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SPECIFIC GRAVITY - Weight of a liquid compared to water.

SPECIFIC HEAT - The ratio of the quantity of heat required to raise the temperature of a body or mass 1° to that requiredto raise the temperature of an equal mass of water 1°.

SPECIFIC VOLUME - Volume per unit (one) mass of a substance.

STANDARD ATMOSPHERE - When air is at a condition of 14.7 psia and 68° F.

STANDARD CONDITIONS - 68° F., 29.92 inches Hg., and R. H. of 30 percent used in air-conditioning calculations.

STRATIFICATION OF AIR - When air lies in different temperature layers because of little or no air movement.

SUBLIMATION - When a substance changes from a solid directly into a gas without becoming a liquid.

SUBCOOLING - Cooling of a liquid below its condensing temperature.

SUPERHEAT - Adding heat to a vapor above its boiling temperature and at the same pressure.

THERM - 100,000 British thermal units.

THERMISTORS - An electrical resistor made of a material whose resistance varies with the temperature.

TRANSISTOR - An electrical device used to transfer an electrical signal across a resistor.

TRIPLE POINT - A condition of pressure and temperature where the liquid, vapor, and solid states can coexist.

VAPOR PRESSURE - The pressure exerted by a vapor upon its liquid or solid form.

VELOCIMETER - A direct reading air velocity meter, reading in feet per minute.

WEB BULB - A dry bulb thermometer with a wick attached to the bulb that is used in the measurement of relativehumidity.

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APPENDIX

REFRIGERANTS

Properties of Liquid and Saturated Vapor

Tables 1 - 6

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67

68

69

70

72

73

74

75

76

Answers To Practice Exercises

CHAPTER 1

1. A generator produces dynamic electricity. (1-4)

2. Voltage is electrical pressure; current is the movement of electrons and resistance is the opposition to current flow. (1-6, 10)

3. These alloys make it possible to operate at high temperatures without melting. (1-11)

4. The cross-sectional area, the length, and the temperature. (1-12)

5. Hardened iron. (1-16)

6. Number of poles and speed of rotation. (2-10)

7. 2 amperes. (3-4)

8. 240 volt. (3-5)

9. 22 ohms. (3-6)

10. One horsepower. (3-25, 27)

11. The symbol for inductance is L. (4-8)

12. The capacitor gives the motor more torque by causing the current to lead the voltage. (4-10; Fig. 17)

13. Only when the circuit is made up of pure resistance. (4-12)

14. No, only on pulsating dc. (5-61)

15. Iron core, primary winding, and secondary winding. (5-2)

16. Wye-wye, delta-delta, and wye-delta. (5-21)

17. To limit the amount of current flow through the meter circuit. (6-3)

18. The shunt is connected in parallel with the ohmmeter circuit to bypass most of the current around the meter coilcircuit. (6-4)

19. Maximum current will flow through the ohmmeter circuit when there is minimum resistance to flow. (6-7)

20. A rectifier must be added to change ac to dc. (6-9)

21. To measure the true power in an ac circuit regardless of the type load. (6-10)

22. To check for a blown fuse the voltmeter is connected in parallel with the fuse. (6-20)

23. To check for continuity in a parallel circuit the unit being tested must be isolated from the rest of the circuit. (6-30)

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24. The speed of an ac motor depends on the number of poles and the frequency of the applied electrical source. (7-2)

25. A single-phase induction motor must have two windings, a start and a run winding. (7-5)

26. The motor would run hot and burn out the start winding if allowed to run any length of time. (7-15)

27. A capacitor start, capacitor run. (7-18)

28. A three-phase motor exerts a torque when at rest, and therefore it starts itself when the correct voltage is applied to thestator field coils. (7-23)

29. The reluctance motor operates at exactly synchronous speed because of the salient poles. (7-26)

30. Universal type motor may be used on ac or dc. (7-28)

31. A motor should be lubricated according to applicable publications. (8-3)

32. Circuit protective devices are used to protect the unit and wires in the circuit. (9-7)

33. Two. (9-11)

34. If the fan circuit is not closed, the air conditioner holding oil circuit will be opened at the auxiliary contacts in the fanmotor starter. (9-12)

35. Most troubles will be found in the load contacts, holding coil, or heaters. (9-14)

CHAPTER 2

1. Intake, compression, ignition, power, and exhaust. (10-1)

2. The engine oil should be checked when he engine is stopped and the oil is at normal operating temperature. (11-4).

3. An air-fuel ratio of 15 to 1 gives maximum economy. (12-4)

4. Pulsating dc. (13-4)

5. The purpose of the capacitor (condenser) in the engine ignition circuit is to help collapse the magnetic field and toreduce arcing at the points. (13-5)

6. Lead and acid. (13-9)

7. Ethylene glycol should be used when the water-cooled engine will be exposed to freezing temperatures. (14-4)

8. With a 10-pound pressure at a point halfway between the compressor pulley and the drive pulley the belt should deflect1/2 to 3/4 inch if the belt is correctly adjusted. (15-3)

CHAPTER 3

1. All molecular movement will cease at absolute zero. (16-2)

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2. Sublimation. (16-3)

3. Cold is not produced but is merely a result of removing heat. (16-3)

4. Sensible heat is the amount of heat that can be added to or subtracted from a substance without changing its state.(16-4)

5. Latent heat is hidden heat and is the heat that is added to or subtracted from a substance when it changes its state.(16-5)

6. The specific heat of water is 1. (16-7)

7. -40° centigrade is equal to -40° Fahrenheit. (16-16)

8. The relative weight of liquids and solids is determined by specific gravity. (16-18)

9. 2117 pounds per square foot. (16-20)

10. 66,000 foot-pounds; 2 horsepower. (16-23, 24)

11. 778 foot-pounds = 1 Btu. (16-25)

12. 100 Btus. (16-26)

13. The critical temperature. (16-28)

CHAPTER 4

1. The critical temperature of water is 689° F. (18-2)

2. If the critical pressure is not above the condensing temperature the gas will not condense. (18-3)

3. The most desirable refrigerant would have a high latent heat of vaporization. (18-6)

4. Ammonia gives off a white smoke in the presence of a flaming sulphur candle. (18-11)

5. A refrigerant cylinder must never be filled more than 85 percent. (18-17, 18)

6. Boric acid solution may be used if liquid refrigerant comes in contact with the eyes. (18-19)

79

SUBCOURSEEDITION

OD 1748A

REFRIGERATION AND AIRCONDITIONING II (COMMERCIAL

REFRIGERATION)

REFRIGERATION AND AIR CONDITIONING II(Commercial Refrigeration)

Subcourse OD 1748

Edition A

United States Army Combined Arms Support CommandFort Lee, VA 23801-1809

14 Credit Hours

INTRODUCTION

This subcourse is the second of four subcourses devoted to basic instruction in refrigeration and air conditioning.

This subcourse explains the components, operation, and repair of commercial refrigeration systems and provides adetailed explanation of the various uses of compressors. In addition, there is detailed instruction on the use and defrostingof storage cabinets, plant design, special systems, and vehicular refrigeration units.

There are three lessons.

1. Commercial Refrigeration Systems.

2. Commercial Refrigeration Systems (continued).

3. Cold Storage, Ice Plants, Special Applications, and Vehicle Units.

Unless otherwise stated, whenever the masculine gender is used, both men and women are included.

PREFACE

THE REFRIGERATION field includes a wide variety of refrigerators, and you must be able to implement themaintenance program that keeps these refrigerators operational. The first chapter is devoted to small commercialrefrigeration units, mainly portable types, such as are used in homes, messhalls, and commissaries. We will discuss theabsorption type refrigerator as well as the more common compressor type used in most domestic refrigerators and freezers.The components, their operation, and the troubleshooting procedures for both types are discussed. Braxing, welding, andcutting methods are explained, and the last section gives repairs and services.

The subject is expanded in the second chapter to other commercial units, such as water coolers, ice cube machines, andlarger equipment like walk-in cabinets and display cases. Large cold storage plants and ice plants merit treatment in aseparate chapter. In Chapter 4 we will discuss systems designed for special application, such as those using multipleevaporators and multiple compressors. This chapter also includes a section on ultralow-temperature systems. As you willlearn in the last chapter, there have been few changes in automotive air conditioning, but there are some brand newmethods for refrigerating food transport trucks.

By becoming familiar with the symptoms that lead to refrigerator breakdowns, you will be able, in many instances, toprevent such breakdowns. Regardless of the type and size of any refrigerator, a specific cycle is followed before therefrigerating effect takes place. Therefore, a thorough knowledge of this cycle and a clear understanding of applicabletroubleshooting procedures should make your job less difficult.

i

ACKNOWLEDGEMENT

Acknowledgement is made to the following companies for the use of copyright material in this memorandum: AlcoValve Company, St. Louis, MO; Controls Company of America, Milwaukee, Wisc.; McGraw-Hill Book Company, NewYork, N.Y.; John E. Mitchell Company, Dallas, Texas; Mueller Brass Company, Port Huron, Mich.; Nickerson and CollinsCompany, Chicago, Ill.; The Trane Company, LaCrosse, Wisc.

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CONTENTS

Page

Preface.......................................................................................................................................................................... i

Chapter

1 Commercial Refrigeration Systems..................................................................................................................... 1

2 Commercial Refrigeration Systems (Continued)................................................................................................ 30

3 Cold Storage and Ice Plants................................................................................................................................ 56

4 Special Application Systems ............................................................................................................................... 71

5 Vehicle Refrigeration Units................................................................................................................................ 85

Answers to Review Exercises.................................................................................................................................. 95

iii

CHAPTER 1

Commercial Refrigeration Systems

THERE WAS A TIME when Grandma use ablock of ice to keep her food from spoiling. Later, amechanical unit replaced the block of ice In those days aservice call often meant airing out the kitchen beforework could be started because the place was full ofammonia or sulfur dioxide fumes. You do not have thatproblem today, for the modern domestic refrigerator usea refrigerant which is practically odorless and harmless.

2. The domestic units explained in this chapter useone of two basic systems: the absorption refrigerationsystem and the compression refrigeration system. Wewill take up the construction of domestic refrigeratorboxes first, since much of this information is common tothe absorption refrigerator and the freezer boxes whichfollow. The discussion of components such as latches.ice cube makers, and other features will also includespecific information relating to their operation, service, ormaintenance.

3. A section on compression system componentsstarts with a brief review of operating principles followedby the components which put these principles into action.The section concludes with refrigerator performancewhich is based on normal operation of the system.

4. Freezers are dealt with by supplying only thatinformation which is necessary. For example, theconstruction and insulation of a freezer box is essentiallylike a domestic refrigerator box, so there would be noprofit in repeating it.

5. Troubleshooting hermetic systems is divided intoelectrical troubles and mechanical troubles. Thediscussion is centered around those components whichare essential to the main system. Other componentswhich have been discussed previously are accessories orspecial features and, as such, they are treated separatelybecause they will vary from one unit to another.

6. A comprehensive discussion of safety introducesthe section on brazing, welding, and cutting. Emphasis isplaced on those fluxes and alloys commonly used by arefrigeration repairman. This is followed by the repairswhich you are normally expected to make on domestic

refrigerators and freezers. The necessary services forcharging a small hermetic system make the finaldiscussion in this chapter. Since most of us are familiarwith the domestic refrigerator, it is the logical startingpoint for your study.

1. Domestic Refrigerators1-1. The recent trend has been to make larger

domestic refrigerators. Consequently, many homes nowuse units as large as those found in small cafes orrestaurants. Such larger units are quite expensive, butthey have been accepted by the buying public because oftheir proven reliability and greater efficiency; 10 years ofcontinuous service is not uncommon.

1-2. Construction and Components. A refrigeratoris made of two steel shells. The outer shell consists ofsteel plates welded to a steel frame, which gives strengthand rigidity. The inner shell is formed from a singlesheet of steel, which must provide the mountingarrangement for the shelves and support the evaporator.The space between the two shells is filled with insulation,and the gap at the edge is closed by the breaker strips.The door is formed from a single sheet of steel and isgiven rigidity by the liner. The door gasket is installed sothat it fits into the gap between the liner and the shell.The body of the door is filled with insulation.

1-3. Insulation. When temperature differences existclose to each other, they always try to equalize eachother. Insulating materials can retard the transfer so thata cooled area will stay cold longer. From your studies,you may remember that heat is transferred byconvection, conduction, and radiation. Convection is thetransfer of heat by air currents. Cells of dead air spacereduce convection by restricting the movement of air.Conduction is the transfer of heat by a medium acting asa bridge from one temperature zone to another. Materialsuch as paper is a poor conductor. Radiation is thetransfer of heat in the same way that light is propagated.Radiant heat can pass through a block of clear ice so thatthe heat can be sensed on the other side. Radiation

1

from a surface is determined by the color and texture ofthe material.

1-4. The greatest heat load in a refrigerator is theheat transferred through the door and walls of the box.Better insulation means less heat gain, greater efficiency,lower operating costs, and an extended life for thecompressor. Among the basic insulating materials used,you will find spun glass, rock wool, cork, plastics, andmetals. These materials are produced as sheets, fibers,cells, or a combination of these. For example, if you willlook at the edge of a corrugated cardboard box you willsee a combination of sheet and cell constructions. Cellsare tubular in cardboard construction, but a honeycombtype of cell will insulate better.

1-5. The manufacture of insulation has been soimproved in recent years that present-day boxes are builtwith a relatively thinner wall. Some new types ofinsulation will sufficiently reduce heat transfer with onlyone-fourth to one-half inch of insulation. Among thenewer insulation materials are steel and aluminum. Thinsheets of metal are made to form a multilayer sandwichwith dead air space between the sheets. However, withsuch metal insulation, in order to prevent theaccumulation of moisture, as with other types of material,it is important that adequate sealing be provided. Amongother new insulating materials are synthetic fibers orplastics which can be molded into a form that will fitbetween the outer and inner shells of a box. Suchmolded insulation has the advantage of eliminatingcorner and edge joints.

1-6. Any insulation must have an effective moisturebarrier provided to insure its long life. Obviously,because some materials will lose their insulating value ifthey get wet, they must be waterproofed. To thesematerials, odorless tars are often applied to seal thesurface and keep the moisture out. Why are such tarsused? Because the taste of food would be ruined ifaromatic tars were used for sealing. Among the methodsof sealing are painting or dipping the insulation in awaterproof compound to close the pores in the surfaceagainst moisture. As a further protection againstmoisture, special rubber gaskets are used to close allspaces where wire or tubing passes through the insulation.In fact, every precaution is taken at the time ofmanufacture to keep moisture from getting intoinsulation. Also when foam insulations are used, they arenonburning if they are made to Federal SpecificationHH1-1-00530 (ASTM 1692). Note, too, that somesynthetics are not only resistant to rot but also have nonutritional value which might support rodents, insects, orfungi. Finally, while all synthetics are not equallyelective, a few have such a low K-factor that when used

for the same purpose, they are equivalent to twice thethickness of many natural materials.

1-7. By now, as a refrigeration specialist, it should beobvious that moisture can cause many troubles. In fact,in an area where air circulation is restricted andtemperature is near 70°, conditions are right to bothpromote the growth of bacteria and result in corrosion ofthe metal. The effectiveness of modern sealing methodsis shown by the rare occurrence of this trouble withinsulation. Still, the complete replacement of insulation isnecessary if flooding has resulted in the seal breakingdown. Such seal breakdown occurs if a box is submergedunder water too long. You can ordinarily make minorrepairs to torn insulation with tape. When you do this,however, paint the patch with a waterproof sealer such ashydrolene, an odorless tar.

1-8. Breaker strips. The gap between the inner andouter shells is closed by means of the breaker strips.These are not required to make an airtight seal, becausethey are found inside the area of the door gasket. Yet,because the temperature in the box is colder than theinsulation space, any moisture will tend to be drawn fromthe insulation. If you have ever removed or replaced abreaker strip, you will know from experience that thosemade from plastic are easily broken. Still, whether theyare made of metal or plastic, these strips require carefulhandling, as kinking will permanently deform the stripand result in a gap.

1-9. Stile or mullion heaters. These heaters are foundin back of the breaker strip on some boxes. They arelow-watt linear elements which operate continuously toprevent frost creepage around the door. This is anotherreason for using care when removing a breaker strip,since it is possible to damage the wiring or the heaterstrip.

1-10. Door gaskets. These gaskets are made of rubberor plastic and follow the general shape shown in figure 1.Note the air pocket, which acts as an air cushion andhelps to insure an airtight seal between the door and thecabinet. Most manufacturers today place the door-closingmagnets in the air pocket of the gasket. In this position,the magnets not only hold the door closed but also insurethe gasket making a seal throughout its life without everneeding adjustment. The strip magnet is installed in thetop, bottom, and .latch side of the door but not at thehinge side, because if placed here, it would tend to closethe door. Older models had one or two large magnetswith steel plates which took the place of a door latch.

1-11. Door latches. In spite of widespread publicity, 44children were reported as having lost their lives in unusedrefrigerators between 1 January and 17 November 1964.Therefore, whenever a refrigerator of the old style is tobe stored, the

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Figure 1. Door gasket.

latch should be removed and taped to the inside of thebox. In shipment, the door can be secured by tape or alength of rope. If you remember these precautions, youwill never have to worry about having contributed to thedeath of a child. In fact, in many states it is against thelaw to abandon a refrigerator without removing the dooror the latch.

1-12. Adjustable door latches were used onrefrigerators for many years before the introduction ofpermanent magnets as door closers. A door latch can beadjusted to compensate for a worn or compressed doorgasket. To do so, release the locking screw and move thelip closer to the cabinet. Use a thin piece of paperbetween the gasket and the cabinet to check the seal.With the door closed on the paper, the amount of dragon the paper as you pull it indicates the amount of sealthat the gasket furnishes.

1-13. Location and Power Supply. A domestic typerefrigerator is often located without consideration of theoperation of the equipment. As you know, these unitsare self-contained, with the condenser mounted under orin back of the box. Thus, the unit cannot operateefficiently if it is placed too close to an oven or to aspace heater. Note, too, that although the originallocation of a refrigerator may have been quitesatisfactory, subsequent installation of heating unit mayinadvertently find the refrigerator in the hottest part of aroom. Furthermore, consideration as to the suitability ofa location should also take into account the distance fromthe power source. A domestic box is provided with acord and plug which can be used in a convenience outlet.As there are usually several outlets on one branch circuit,it is possible that a branch circuit is being operated atclose to capacity. A refrigerator will be operating onmarginal current under these conditions. If it isconnected to an outlet which is last on the circuit, thevoltage drop may be so great that the unit will not givesatisfactory performance.

1-14. At most overseas bases, where there aregovernment furnished quarters, refrigeration equipment isdesigned for the voltage and frequency of the electricityin the local area. However, you may find that somerefrigerators made for 60-cycle operation have beentransported over seas and are being used on 50-cyclecurrent. If the voltage is correct, the unit may givesatisfactory operation on the lower frequency. Voltageand frequency are just two of the many new things youshould be aware of when you are on an overseasassignment. Refrigerator made for overseas use withunusual electric requirements have a notice posted insidethe box stating the specifications.

1-15. Combination Refrigerators. Since the freezersection has increased in size, practically all boxes made inthe larger sizes today are combination refrigerators.Continued improvement has led to such things asautomatic ice cube makers, forced-air circulation, frost-free operation automatic defrosting, and even ultravioletlamps, which retard bacteria growth and reduce odor.New developments have resulted in more usable cubicfeet in the box by reducing the size of the compressorand the insulation space. Most new units use Freon 22,because it is more efficient, requiring less horsepower forequivalent output. As the demand for refrigerators hasincreased, it has brought about the development ofspecial-purpose storage compartments for different foods.

1-16. Special compartments. Meat storagecompartments are kept at slightly above freezing. withhigh humidity-as high as 90 percent. These conditionsare favorable for extended storage of unwrapped foods.High humidity prevents desiccation, and the near freezingtemperature retards bacterial action.

1-17. High-humidity storage for leaf vegetables, suchas lettuce and celery, is provided by drawers located inthe bottom of the refrigerator section. Another special-purpose compartment is the butter conditioner, which islocated in the door. Butter is maintained at a warmertemperature here than elsewhere in the box so that it willnot be too hard for serving. Two methods are used toget the proper temperature for this compartment. Forone, when an electrical heater is used, a rheostat is variedto get the desired heat. The heater element is connectedto the electric supply whenever the compressor isrunning. A flexible cord is used at the door hinge tobring the circuit into the door. For the other, when aheater element is not used. the butter conditionerdepends on the heat passing through the door at thatplace to keep the butter from getting too hard. Theinsulation thickness at that place in the door determinesthe rate of transfer of heat.

1-18. Automatic ice cube maker. An automatic ice cubemaker is a specialized item found

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in the freezer compartment of some boxes. One popularmake uses a solenoid valve, an electric motor, an electricheater, a feeler bulb, and two thermostats. A mechanicalvalve (globe valve) in the water line is adjusted to reducethe line pressure so that the correct amount of water willbe metered into the ice cube tray. This valve will needadjustment if there is a change in supply water pressure.One thermostat senses when the ice is made, and theother thermostat has a feeler bulb in the storage traywhich senses when the tray is full. Let us consider theautomatic operation, starting with the completion of abatch of ice cubes. Sensing that the water is frozen andthat the cubes are ready to be used, the "cold" thermostatenergizes the electric heater in the tray. The "hot"thermostat senses when the tray is warm enough torelease the cubes, at which time this thermostat starts theelectric motor. The motor accomplishes the followingoperations as it goes through one cycle: It resets the"cold" thermostat and turns off the heater. Mechanicalfingers sweep the cubes out and into the storage tray, andthe solenoid valve opens the water line to refill thefreezer tray. The solenoid valve remains open for aninterval determined by the motor operation which closesthe solenoid valve at the end of the interval. The motorestablishes its own holding circuit when it starts, and itopens this circuit when the cycle is completed. (NOTE:We are dealing here with a time sequence in which somethings happen together, while in others there is anoverlap of action involved.) Ice cubes will not be ejectedif the storage tray is full, because the feeler bulb in thetray will interrupt the circuit of the "cold" thermostat.As soon as enough cubes have been removed, the heaterwill be turned on to release the cubes in the tray andstart another cycle.

1-19. Automatic defrosting. One of the earliestschemes to defrost an evaporator was the manualpushbutton which started the cycle. When defrostingwas completed, the compressor was automaticallyrestored to normal operation. By contrast, today thereare defrost systems which are completely automatic. Wewill discuss the more common such systems. One such,a mechanical system, uses a counter which registers eachtime the door is opened. After a certain number ofopenings, the device starts the defrost cycle. This systemfollows the idea that each time the door is opened thecoils will accumulate some moisture, and afterapproximately 60 openings, defrosting will be necessary.

1-20. An electric clock is used in three basic systems.In one system, the clock may be wired in parallel withthe compressor so that it measures the total running timeof the compressor. The theory here is that after 6 hoursof compressor operation, the coils should need defrosting.

In another such system, a clock is wired in parallel withthe cabinet light so that the clock measures the length oftime that the door remains open. The advantage of thesetwo systems is that they indirectly reflect the heat loadon the unit. In still another system, one utilizing hotwire defrosting, a 24-hour clock, which is set to defrost at0300 hours, simultaneously opens the circuit to thecompressor and turns on two heaters. Instant heat issupplied by one of the heaters, which is similar to thatused on an electric range. The insulated heater wire isinstalled either alongside the evaporator coil or in thecenter of the tubing which makes the coil. The otherheater is a low-wattage heater used to keep the drain freeof ice accumulation. A 70° thermostat, when satisfied,resets the clock mechanism. The heaters are turned off,and the compressor circuit is made ready for operation.

1-21. Defrosting must be scheduled whenever thefrost accumulation has reached 1/8 inch thick.Otherwise, the layer of frost will act like an insulatingblanket which slows down the transfer of heat.

1-22. Hot gas defrosting, still another method, utilizesan electrically operated solenoid valve controlled by aclock or some other timing device. Figure 2 shows thesolenoid valve open. This position allows the hot gasfrom the compressor to pass through the evaporator.When the defrosting period ends, the valve closes andthe compressor will return to normal operation.Accumulated melt

Figure 2. Hot gas defrost system.

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water is caught in a drain trough and piped to a tray inthe compressor compartment for evaporation. Youshould remember from your study of fundamentalrefrigeration principles, that the capillary tube, shown infigure 2, is universally used as the expansion device in asmall system. It has the advantage of no moving parts,and the pressures are equalized after the compressor stopsso that there is less starting torque on the motor.

1-23. Special Features. Two special features which arefound in some boxes are ultraviolet lamps and circulationfans. Ultraviolet lamps are wired into the circuit forcontinuous operation. Their radiation kills bacteria andcounteracts some disagreeable odors. Circulating fans areused to give positive ventilation and to insure frost-freeoperation with proper control of humidity. Theventilation channels, between the freezer and therefrigerator, must not be blocked by storage containers.The motor-driven fan is wired in parallel with thecompressor so that the fan circulates air during thecooling period. A switch in the line to the fan opens thefan circuit when the refrigerator door is open. The fanswitch may be incorporated with the door switch thatcontrols the cabinet light. Do not confuse this fan withthe one used for cooling a compressor and a condenser.Food stored in a box with forced circulation must becovered to prevent desiccation. Also, if much uncovered,moist food is stored in such a box, it will cause excessivemoisture to accumulate in the freezer. This excessivemoisture will, in turn, cause frequent defrost cycling andcompressor operation, which may lead to complaintsabout "defective equipment."

2. Absorption System Refrigerators2-1. For many years, the absorption system has

proved satisfactory for domestic refrigerators. Largecapacity absorption systems are covered in Volume 4.Boxes made for use in the United States are designed touse either natural, liquid petroleum, or artificial gas heat.(In Europe, boxes have been made which use electricityfor heating.) Absorption system refrigerators are madewith automatic defrosting and ice cube makers. Thedefrost system is the electric hot wire type, with a timersuch as is found in conventional boxes. The automaticice cube maker is of the type which we have explained inSection 1 under the same title. Identification plates arelocated in the frozen food or the control compartment.

2-2. Each burner must be provided with the correctsize orifice for the gas supply to which the refrigerator isconnected. Gases are rated in B.t.u. per cu. ft., with LPgas the highest at 1600 B.t.u. per cu. ft. If you willcompare two nozzles for size. You will see that the onefor use with LP will have the smaller orifice. The nozzle

with the larger orifice is used with natural gas. which hasless heat value.

2-3. The most popular domestic refrigerator of theabsorption type uses an ammonia-water cycle in anatmosphere of hydrogen. The system is pressure testedat 800 p.s.i.g., but normal pressure in the system is 200p.s.i.g. A fuse plug will release the pressure in the systemif temperature rises to above 175° F. This release ofpressure prevents any accidental explosion of the system.

2-4. Construction and Components. The absorptionrefrigerator box is constructed and insulated in much thesame way as we have explained previously in this chapter.The essential parts of an absorption system are agenerator, a vapor separator, a condenser, an evaporator,and an absorber. Among the components are someitems which may sound unfamiliar. The generator is thatart of the system where a water-ammonia solution isheated. The vapor separator is a special chamber wherethe water is separated from the ammonia. The absorberis so named because water at this place absorbs ammoniavapors. A brief review of the principles involved is givennext.

2-5. Operation. The principle of operation of anabsorption system depends upon the strong affinity whichwater has for ammonia. When the water-ammoniasolution is heated in the generator, a mixture of waterand ammonia vapors is given off. This vapor mixturerises to the vapor separator, where much of the moistureis extracted and returned to the generator by way of theabsorber. Ammonia vapors rise in an atmosphere ofhydrogen to the condenser, which is cooled by airtemperature, and the ammonia liquefies. Liquidammonia falls into the evaporator. The area in theevaporator has a concentration of hydrogen, whichencourages the ammonia to vaporize and absorb heat.The evaporator is located in the freezer compartment ofthe box. From the evaporator, the ammonia vapor fallsto the absorber, where it joins the water (from the vaporseparator) returning to the generator, thereby completingthe cycle. The system is completely closed, and there areno adjustments possible, except to the flame whichsupplies heat to the generator. The flame operatescontinuously, and any changes in heat load are met bychanging the size of the flame. This adjustment is madeautomatically by a thermostatic control which regulatesthe gas supply to the flame. The sensing element islocated in the freezer compartment. You will findseveral items between the unit and the gas line in aninstallation of this type. Starting from the gas line, theseare a shutoff valve, a filter, a pressure regulator, and a gasburner with an automatic control. The gas burner valveis provided with a safety feature which will

5

shut the gas off if the flame should be extinguished. Inthe order in which the device is implemented, the safetyconsists of a heater, a snap button, and a poppet valve.The snap button is linked to the poppet valve. The snapbutton is a curved piece of metal which reverses its curvewhen it is heated. The heater is located in the flame andconveys heat to the snap button. As long as the snapbutton is hot enough, it will hold the poppet valve open.If the flame fails, the snap button will reverse itself andclose the valve, shutting off the gas. To light the flameagain, you will have to heat the heater with a match andpress a pushbutton to rest the poppet. If the heatershould be accidentally dislodged from the flame duringcleaning, the flame would be extinguished. The simpleremedy for this condition is to move the heater back intothe flame path and relight the unit.

2-6. Maintenance. To maintain an absorptionrefrigerator, you need only to keep it clean. Especially,remove all soot from the flue and burner chamber, sinceit acts as an insulator when it accumulates and thusprevents the generator from getting enough heat to do itsjob efficiently. Also, keep the flue clear of obstructions,since the flue draft is designed to work with the burnerfor best operation. In addition, keep dust accumulationsoff the condenser so that it will be able to transfer heat.This is important, since the condenser in an absorptionsystem is more sensitive than that in a conventional typerefrigerator. The only adjustment that you can make isto the flame to insure that it is clean and that it gives aminimum of carbon. A flame which is too yellow giveslow heat and will not give satisfactory service because theflue will gather excessive soot and need cleaning toooften.

2-7. An important aspect of correct installation of anabsorption refrigerator is to be sure that it is placed level.When checking with a level, be sure that you check theunit rather than the box. Why? Because unless the unitis level, the system cannot operate properly. On theother hand when a unit is level, it will work correctlyeven if the box is slightly out of plumb.

2-8. When a box is placed in service after havingbeen left idle for an extended period of time, it may notfunction at a cool enough temperature to make ice cubes.One suggested remedy for this condition is to remove theunit from the box and turn it upside down for an hour.Then install the unit and reconnect it to the gas line.Thereafter, it should function properly when fired up. Ofcourse, you might find it simpler to disconnect the gasline and turn the whole box upside down for an hour.Otherwise, the main reasons for poor unit operation arean incorrect flame and/or too much dirt clogging theheat exchanger surfaces.

3. Compression System Refrigerator Components3-1. The main parts of a domestic type refrigerator

are discussed in this section. These are compressors,condensers, evaporators, and refrigerant controls. Wewill cover the common types of each and their variousapplications. The hermetic system is used with alldomestic boxes. We will also discuss refrigeratorperformance as it relates to the components ofcompression system refrigeration.

3-2. Reciprocating Compressors. The operatingprinciple of a compressor is closely related to therefrigeration cycle. A brief review of the principles ofrefrigeration is appropriate at this time. When a gas iscompressed, it gets hotter. When pressure on a gas islowered, it gets cooler. When a liquid becomes a gas, itpicks up heat. The gas passing through a compressor getshotter. It gives up this heat in the condenser, where itbecomes a liquid. It changes from liquid to gas in theevaporator, where it picks up heat (cools the evaporator)and carries this heat through the compressor back to thecondenser, where it is again cooled. The function of thecompressor is to make the required pressure changes onthe refrigerant so that it can do its work. High pressureis on the condenser side (high side) and low pressure onthe suction side (low side).

3-3. The reciprocating compressor consists of acylinder and head, a piston and connecting rod, intakeand exhaust valves, servicing valves, fly-wheel, crankshaftand crankshaft seal, and suction strainer. Clearances assmall as 0.0001 inch are possible between the movingpans, because the compressor is operating in a closedenvironment where the temperature range is relativelynarrow.

3-4. The piston may be driven in a number of ways.In one, the crankshaft may be like the kind used inautomotive engines. Another type uses an eccentriccrankshaft which operates like a cam. Still another is thescotch yoke mechanism which uses a pin mounted offcenter to the crankshaft. A sliding member inside thepiston permits the rotation of the pin to be translatedinto up-and-down motion. Variations such as these arepossible because gases are being pumped which do notproduce heavy bearing loads. The piston is made tocome as close as possible to the head without touching.Clearance may be as little as 0.01 inch at top dead center.

3-5. Exhaust and intake valves are usually made ofthin disks of steel which seat against shoulders in thevalve plate. These valves are sometimes called flutter orreed valves. Pressure in the cylinder closes the intakevalve and raises the exhaust valve on compression. Onthe intake stroke, pressure in the suction line opens theintake

6

valve, while back pressure from the high side closes theexhaust valve. Valves are designed to operate at amaximum lift of 0.10 inch. Beyond this point, the valvegets noisy.

3-6. Rotary Compressors. Fewer moving parts andless vibration are advantages of the rotary, which is madein two styles. One style uses an eccentric shaft withblade which is forced against the shaft by a spring. Theblade slides back and forth in a slot in the case betweenthe intake and exhaust. As the shaft turns, it traps a gascharge at the intake and sweeps it around to the exhaust.Oil makes the seal for the blade so that the gas will becompressed.

3-7. In another style of rotary, vanes are mounted inslots on the shaft. The shape of the case around thevanes is eccentric. Centrifugal force holds the vanes incontinuous contact with the eccentric wall. The inletport is located in the wall furthest from the shaft, at thespot where a gas charge is picked up between two vanes.As the shaft turns, the space between the shaft and thewall becomes smaller, compressing the charge of gas.The exhaust port is set in the case where the shaft almostrubs against the case. The compressed charge of gas isforced out the exhaust at this point.

3-8. The exhaust valve is a flapper type made ofspring steel. A muffler is placed in the high-pressure lineto suppress the popping noise which accompanies therelease of a gas charge. The suction line is provided witha check valve to prevent gas from leaking back when thecompressor is stopped. The suction strainer prevents dirtparticles from entering the compressor.

3-9. Condensers. Among the kinds of condenserswhich you should know are (1) the finned coil withforced convection, (2) the finned coil with naturalconvection, and (3) the plate condenser with naturalconvection. Coils may be mounted in an upright, aninclined, or a horizontal position. The first few turns ofcoil may be placed under the pan which collects waterfrom defrosting. Evaporation of this water aids thecondenser in dissipation of heat. Between the condenserand the evaporator is a capillary tube firmly soldered tothe suction line in order to operate as a heat exchanger.

3-10. Evaporator Arrangements. While onecondenser may serve a combination refrigerator, there arethree general arrangements for the evaporator to cool thetwo areas. In one arrangement, the evaporator coil in thefreezer is extended into the refrigerator compartment. Arestrictor separates the two sections of the evaporatorcoil, as shown in figure 3. The capillary tube is omittedfor simplicity. The refrigerant goes first to the coolingcoil, which is forced by the restrictor to operate at ahigher pressure and temperature. After passing therestrictor, the refrigerant is at a lower pressure andabsorbs sufficient heat to drop the temperature in the

freezer to the desired low range. The restrictor used insome refrigerators is a weighted valve, and the methodemployed is called a weighted valve system.

3-11. A box which uses a weighted valve must beinstalled level to insure proper operation. If the positionof the valve is disturbed from the correct position, thebox will not perform properly. For example, certainboxes use a weighted valve which is designed to operateproperly at an angle of 60° from the horizontal. If thevalve is tilted too much toward the vertical, the foodcompartment will get warmer. On the other hand, toomuch tilt toward the horizontal will make the fresh foodcompartment colder. The indication of this trouble iscontinuous operation of the compressor and partialfrosting of the food compartment evaporator coil. Eitheror both symptoms may be present.

3-12. The second arrangement uses an evaporator coilin the freezer compartment in combination with asecondary closed loop coil. This secondary coil acts asboth a condenser and an evaporator. You can see infigure 4 that part of the closed loop is in the freezer.This part of the coil acts as a condenser, while the rest ofthe loop in the refrigerator acts as an evaporator. Onemajor

Figure 3. Dual temperature system.

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Figure 4. Closed secondary system.

advantage of this is that the closed loop can be designedto operate frost free.

3-13. A third arrangement uses one of severalcombinations of the first two methods. These variouscombinations are designed with the object of eitherautomatic defrosting or frost-free operation. Some ofthese combinations rely on air circulation to get betterresults. Slots between the two areas will allow convectioncurrents to circulate, or a fan may be used for forced airto insure a more uniform temperature.

3-14. When only one coil forms the evaporator in thefreezer compartment, it is called "air spill over." Themethod is called "refrigerant spill over" when two coilsare used in series. When a separate evaporator is used toform a closed loop the method is known as a secondaryrefrigerant system.

3-15. Regardless of which arrangement is used for theevaporator, the system depends on a capillary tube withits heat exchanger function for proper operation.

3-16. Capillary Tubes. A capillary tube is used tocontrol the refrigerant by placing a restriction in theliquid line. It is sometimes called a choke tube, a moredescriptive name. The inside diameter and the length ofthe tube are critical factors. The diameter of the tube

determines the restriction which it will have to controlthe flow of refrigerant. The length of the capillary mustbe long enough so that the liquid will have started tochange to a gas as it nears the end of the tube. Aselected portion of the tube is soldered to the suction lineforming a heat exchanger. The length of the heatexchanger is calculated in the design so that the capillarywill deliver liquid at the proper temperature. If the solderconnection is broken, the heat exchanger will be lost, andthe unit will not perform properly.

3-17. Starting Relays. At one time, the thermostatwas used directly to control starting and stopping thecompressor motor. The feeler bulb in older units waslocated in the freezer compartment. In somerefrigerators, the feeler bulb is above a small access panelin the top of the freezer. Now, you will find that mostrefrigerators are provided with a starting relay, whichprovides two advantages: First, the relay can be locatedclose to the motor. Second, the relay can handle themotor current more easily.

3-18. Changes in temperature in a refrigerator causeoperation of the thermostat, which controls operation ofthe relay. The starting and stopping of the compressormotor is under the control of the relay. Thecharacteristics of the motor (current and internalresistance) will determine the size of the relay used withit. Since these relays are sensitive to temperaturechanges, they are located where they will be least subjectto changes. The three most common types are (1) thecurrent relay; (2) the voltage, or potential, relay; and (3)the hot wire relay. We will discuss the operation of eachso that you will understand the troubles you might find.

3-19. Hot wire relays. One type of hot wire relay usestwo bimetal strips and two heater resistors. In figure 5,there is a schematic diagram which shows theconnections for the relay and motor. The motorterminals are identified by C for common, R for run, andS for the start winding. When the motor control closes,electricity is applied to both the running and the startingwind-

Figure 5. Hot wire relay.

8

Figure 6. Current relay.

ings. The capacitor in the circuit of the starting windinggives the motor more starting torque. The resistor, inseries with the bottom bimetal strip is designed to heatenough of the starting current so that it will cause thebimetal strip to bend up. This opens the circuit to thecapacitor and the starting winding. The bleeder resistoracross the capacitor keeps the relay contacts from beingburned. The upper bimetal strip is heated by the upperresistor by the current going to the running winding. Aslong as the current to the running winding is normal,there will not be sufficient heat to make the upperbimetal strip open. Thus, you can see that the strip inthe "run" circuit acts as an overload device. The currentin the "run" resistor also serves to keep the bimetal stripin the start circuit from cooling so that its contactsremain open until the motor stops. If, for any reason,the motor current becomes excessive, the overloadcontacts will open and stop the motor. However, adisadvantage of this overload protection is that as soon asthe device cools, the contacts will close and the motorwill start again. It will then short-cycle until the circuit isopened. Failures such as this are rare, however. Avariation of the hot wire relay uses a wire under tensionto operate the contacts. In any case, the hot wire relayhas been proved reliable in thousands of commerciallymade refrigerators.

3-20. Current relays. You will find that figure 6 is aschematic diagram of a current relay. Many refrigeratorsare equipped with this type of relay. For the sake ofvariety, this schematic shows a diagram which is typical

of the control circuit for a water cooler. The onlyessential difference between this and the circuit for arefrigerator is the freezestat. Its purpose is to prevent thechilled drinking water from being frozen. The freezestatwill stop the compressor motor (if the thermostat doesnot) to prevent the formation of ice which could damagethe tank. The thermal overload protects the motor fromburning out by opening the circuit if the motor draws toomuch current. Excessive heat from the resistors makesthe bimetal strip bend, which breaks the circuit.

3-21. Operation of the current relay occurs as soon asthe thermostat closes the circuit to the motor. Theinrush of current to the running winding is strong enoughso that the coil pulls the armature up and completes thestarting winding circuit. This happens in a fraction of asecond, putting the starting winding and its capacitor inthe circuit. As the motor approaches its operating speed,the motor current drops because of counter electromotiveforce (cemf). The coil in the relay is designed so that itwill release when the motor r.p.m. passes three-fourthsof its normal speed. The current in the relay coil is notsufficient to hold the weight of the armature when themotor is operating at its normal speed; therefore, therelay contacts open. A bleeder resistor is connected inparallel with the capacitor. Its purpose is to prevent ahigh-voltage discharge from the capacitor, which wouldburn the contacts in the relay as they open. Anadvantage of using a current relay is that the contacts inthe thermostat are

9

only required to close on the inrush current to therunning winding. Furthermore. the contacts in the relayare only required to carry the inrush current to thestarting winding.

3-22. Servicing (i.e. troubleshooting) a current relayconsists of checking the circuits for proper operation. Asthere are no adjustments, a relay which does not operateproperly must be replaced. If the relay contacts are badlyburned, the bleeder resistor should be checked for correctresistance. Some capacitors have the bleeder resistormade as an integral part of the capacitor. If the resistoris found defective, a new resistor of the correct wattageand resistance can be connected across the capacitor tomake a repair.

3-23. Testing a current relay can he confusing. Atleast one maker uses a metal washer as the armature.When the coil is not energized, the washer lies (on thebottom of the case. You can hear it rattle when the caseis tapped. If you did not know better, you might assumethat something had broken loose and that therefore itwas defective. Also, a relay of this make might bedefective even though you could hear no rattle as thearmature could be welded to the contacts. In addition,current relays are sensitive to position; consequently, they

must be mounted horizontal or level to insure properoperation and normal life.

3-24. Potential relays. A voltage sensitive, or potential,relay will have its coil connected in parallel with thestarting winding of the compressor motor. Theschematic diagram in figure 7 is typical of the wiring of amotor provided with this type of relay. The defrostswitch and circuits associated with it have been discussedalready in the first section of this chapter. The contactsof the thermostat must be heavy enough to carry theinrush starting current to the compressor motor. Anadvantage of the potential relay is that the relay contactsare normally closed. Even so, the capacitor dischargeacross the relay contacts when they open may cause themto burn and be welded together. Thus, a bleeder resistoris required across the capacitor to prevent any welding ofthe contacts. The value of resistance for a bleeder isusually 15,000 ohms, and it is rated at 2 watts.

3-25. Operation of the potential relay does not occuruntil the motor passes three-fourths of its speed. Therelay coil is voltage sensitive and requires considerablymore than the line voltage to make it operate. When thethermostat contacts close, the motor starts, because bothmotor windings are energized. The contacts in the relayare

Figure 7. Potential relay.

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normally closed. As the motor approaches its operatingspeed, the current decreases. Induced volt age in thestarting winding now becomes greater than the appliedvoltage. The reason for this lies in a transformer actionbetween the two windings in the motor. The voltagesensitive coil in the relay is sufficiently energized to openthe contacts in the starting winding. The relay remainsenergized by the voltage induced in the starting winding.When the thermostat opens, the motor stops, and therelay contacts return to the closed position.

3-26. Servicing a potential relay consists of checkingthe coil and the contacts for continuity if troubles arcsuspected. Like other relays, the potential relay issensitive to position and must be mounted level to insureproper operation and normal life. Since there are noadjustments, a defective relay must be replaced. A badlyburned set of relay contacts would indicate that thebleeder resistor should be tested and replaced if it isopen.

3-27. Resistors. A bleeder resistor should have aresistance between 15,000 and 30,000 ohms, dependingon the size of the motor and the capacitor. A 2-wattrating is satisfactory for a refrigerator. The wattage ratingis stamped on the body as "2 W." A resistor which iscolor coded will have bands of color painted on the body.Here are four examples:

Decimal multiplierOhms First band Second band Third band15,000 Brown (l) Green (5) Orange (000)20,000 Red (2) Black (0) Orange (000)25,000 Red (2) Green (5) Orange (000)29,000 Red (2) White (9) Orange (000)

3-28. Refrigerator Performance. So that you canevaluate the operation of a refrigerator, analyze troubles,and take the most economical means of repair, you mustknow its performance characteristics. Some of thefactors which you should consider are these: electricalconsumption, percentage of compressor running time,relative temperatures and types of use, vibration or noise,and continuous operation. Relative temperatures, ofcourse, include room temperature and room humidity(mentioned below) and the temperature, respectively, ofthe freezer section and the refrigerator section (notdiscussed below). Continuous operation, althoughdiscussed below, is caused by troubles not normallyconsidered in refrigerator performance.

3-29. Electrical consumption is figured in kilowatt-hours per 24-hour period. You may obtain a recordingtype meter from the electric shop on the base or fromthe local utility company when an actual test is necessary.You may compare the results with standard test curves

furnished by the maker of the box. A modernrefrigerator may use from 2 kilowatt-hours to 8 kilowatt-hours in a 24-hour period, depending on the size of thecabinet and the difference between cabinet and roomtemperature.

3-30. The percentage of compressor running time isaffected by various variable conditions, but normal use ina 75° F. room will require the compressor to operateone-third of the time. Any large increase in running timeindicates there are abnormal conditions. For example,setting the thermostat for a refrigerator temperature of20° F, when a temperature close to 38° is considerednormal will increase the compressor running time.

3-31. Relative temperatures and type of use are justtwo of the variables which affect performance. Increasedroom temperature and room humidity put a heavier loadon the compressor. A difference of 20° roomtemperature may double the running time and electricpower used. Higher humidity will produce frost at agreater rate causing a reduction in evaporator efficiency.Type of use includes frequency and duration of dooropenings as well as the foods stored in the refrigerator.Uncovered liquids will cause an automatic defrost to cyclemore frequently. Unusual load would also result if thefreezer is required to make a great many ice cubes.

3-32. Vibration or noise is rare in the modernrefrigerator as the capillary tube system used by mostmanufacturers requires no moving parts except for thecompressor and the motor. Vibration may result from adefective mounting. For instance, one of the morecommon causes is failure to release the holddown boltsfor the compressor, which were installed before shipmentof the cabinet. On the other hand, a unit will be noisy ifit is low on oil. Thus, if a leak has developed, requiringthat refrigerant must be replaced, then it is likely that oilhas also been lost and must be replaced. One clue towatch for is this: A noisy capillary tube will usuallyindicate low refrigerant, and this results in gas noisessuch as bubbling or hissing. Of course, low refrigerant isalso indicated by a partially frosted cooling coil andcontinuous compressor operation. In the latter event,low- and high-side pressures will be lower than normal.You should also not that a capillary tube which is cloggedor pinched will show a high vacuum on the low side andan abnormally high head pressure.

3-33. Continuous operation can be caused by adefective thermostat, one which does not cut thecompressor off. Any abnormal condition which causescontinuous operation may be obscured at the time youare called because overheating may cause the motoroverload protection to operate. Thus, when you get tolook at the unit, you may find it short-cycling; that is, theoverload device will be shutting the unit off. When itcools enough, the unit will start again. A fast check of

11

this can be made by feeling the temperature of the motorand compressor with your hand. Many compressors nowhave the overload protector inside the shell, where theheat from the motor will prevent the unit from short-cycling. One last item which is often overlooked is lowline voltage, which will make a motor run slow andoverheat. Where a television set is used in the samebuilding as the refrigerator, low line voltage is indicated ifthe picture fails to fill the tube. This is one way ofverifying low voltage when a voltmeter is not available.You must remember to consider all of the factors whenyou evaluate the performance of a unit.

4. Freezers4-1. Many homes today have domestic freezers for

the storage of large amounts of frozen foods. Thesefreezer cabinets are either of the upright style or of thechest style and range in size from 15 to over 25 cubicfeet. In such freezers the capillary type system with ahermetic unit is widely used. Also, in many cases, thecompressor employed is similar to those used forrefrigerators. Upright freezers are supplied with forced-air circulation when they are made for frost-freeoperation. Automatic defrosting is done by the hot gasor the hot wire method used in combination refrigerators.Because of the similarity of the two systems,troubleshooting a freezer can be done by the same rulesas for a refrigerator. Troubleshooting a hermetic systemfollows this section. The construction features of afreezer are often the same as a refrigerator. Therefore,the information here is concerned with those featureswhich apply to freezers.

4-2. Operation and Care. The operatingtemperature for domestic freezers is in the range of 0° F.to 10° F. Each such freezer is equipped with athermostat so that it can be adjusted to satisfy the user'sdesires. Most foods are already frozen when placed instorage, but when nonfrozen foods are placed in thefreezer, it would be desirable for the user to move thecontrol to a colder position in order both (1) to insurefaster freezing and (2) to prevent the thawing of otherfoods. Food must be stacked so as not to interfere withair circulation, as this would cause warm spots to developin the cabinet. Food must also be wrapped in moistureproof and vaporproof material to prevent desiccation.

4-3. A freezer cabinet in normal usage will requiredefrosting about twice a year. Frost may be removed bymeans of a scraper, such as a wooden paddle, or with astiff fiber brush. Use care not to damage the finish.When you desire a complete defrosting, however, removeall frozen foods and store them in dry ice to prevent

thawing. Then shut off the power and use warm waterto hasten melting of the ice. Of course, you should nevertry to chip ice from coils, as such action might damagethem beyond repair. Also, wash the box with a solutionof baking soda or ammonia, and always dry the inside ofthe box before putting it back in service.

4-4. Construction Features. To prevent frostingaround the door, a mullion heater of low wattage isinstalled in back of the breaker strip. By this means, too,sweating around the door is virtually eliminated, becausethe heater is operating continuously. Fiberglas, rockwool, and certain synthetics are used for insulation ofpresent day freezers. Consequently, where formerly a 3-to 4-inch thickness of insulation was used in cabinets, youmay now find them built with walls less than 2 inchesthick. Yet, because of the colder chest temperature,freezer insulation must be better protected againstmoisture than that in a refrigerator. The most effectivemethod for accomplishing this has been found to be acombination of venting and sealing. Venting is providedto prevent a partial vacuum which would occur in asealed box as the temperature of the air is lowered. Ifthe insulation scaling is to be effective, however, it musthave greater resistance than the venting. Thus, the ventwill allow box pressure to equalize while the seal remainsintact.

4-5. Freezer Failure and Alarms. Within 24 hoursafter a freezer fails, the foods it contains will start tothaw. If this is discovered in time, dry ice can be used toprevent the thawing while repairs are made to the unit.Otherwise, meats and fresh frozen fruits must be usedquickly, as it is new satisfactory-or safe-to freeze them asecond time. To avoid this situation, alarm devices aremade which will signal a rise in temperature to 15° F. inthe cabinet. The alarm is given by both visual andaudible means. Two kinds of alarms are available. Oneis made for operation on a 6-volt battery. The other ismade for operation on a 110-volt circuit. The lattershould be plugged into a branch circuit different fromthat used for the freezer. The thermal element should belocated in the upper part of the cabinet, where it willreflect a rise in temperature quickly. While such alarmdevices are not generally supplied for domestic units, theycan be installed in any freezer cabinet.

4-6. In the next section, we will deal withtroubleshooting hermetic systems. You will not find anydistinction between refrigerators and freezers, becausethey both use the same kind of hermetic systems. Themain difference between refrigerators in general andfreezers is that only part of a refrigerator is held at nearzero temperature.

12

5. Troubleshooting Hermetic Systems5-1. The sealed system preferred for freezers and

refrigerators is called a closed or hermetic system. Theshell which contains the motor and compressors iswelded shut, thus the name “sealed unit?” The motorleads pass through a glass insulator, which is bonded tothe metal to insure a joint that will never leak. The onebig advantage of a hermetic compressor is that there areno seals where leaks can develop. This eliminates at leastone trouble spot from the system used in domesticrefrigerators and freezers. But, as you know, there arestill enough other trouble spots to keep a servicemanbusy.

5-2. The best troubleshooter puts his brain to workbefore reaching for the toolbox. The first action on thejob should be to question the user. Ask him, forexample, these things:

• When did you first notice this trouble?

• How often does it happen?

• Does it happen at night as well as during theday?

• Has the unit been making a strange noise?• Is this condition intermittent or is it continuous?

• Does this happen on just certain days of theweek?

The answers to such leading questions should enable youto determine whether the trouble is being caused bymisuse. By eliminating outside factors at the beginning,you will know that you are dealing with a fault in theequipment itself. After this, consider the possibleelectrical troubles first, as they can usually be checkedeasily and quickly.

5-3. Electrical Troubles. There is a logicalsequence which should be followed in making tests onthe electrical system. The first check seems so simplethat it is often overlooked. Remember, the unit cannotoperate without electrical power. A quick reference forcommon faults is given in table 1, together with thepossible causes and their remedies. Such a trouble chartis most useful, since it presents a great many facts in asmall space. In addition, you will sometimes find thesolution to a problem while studying a troubleshootingtable, even though the specific fault does not appear inthe table. Often, in fact, a common fault is passed bybecause it seems too obvious. The serviceman may thinkthat a common fault is too easy and could not possibly bethe trouble he was hunting. Do not prejudge; instead,make reasonable "guesses" from what you see and thetrouble chart, then test to find out the practical results.In the following paragraphs, we have given you a detailedexplanation of the most likely troubles to be found in theelectrical system.

5-4. Power supply. Check the source of powerfor voltage to the unit. How? With a voltmeter or amultimeter! In the case of a refrigerator, open the door.If the light does not come on, there are severalpossibilities: (1) the power circuit is incomplete to theunit; (2) the lamp is burned out; (3) the door switch isdefective; (4) the circuit to the unit may be good, but thewires to the lamp and the door switch are brokensomewhere in the box. If the lamp lights, you will knowthat there is power to the unit. However, check thevoltage with an accurate voltmeter when you suspect lowvoltage. Remember: The line voltage may vary 10 to 15volts with changes in the load during the day. Most unitswill not show difficulty unless the voltage drops below105 volts.

5-5. Overload protection and controls. Make surethat the extension cord is disconnected be, fore making acontinuity test on the protector. With an ohmmeter or atest lamp, check for a continuous circuit through theoverload protector. If it tests open, you have found atleast one trouble which will prevent the compressormotor from operating. Replace a defective overloadprotector and check the unit for normal operation. Manycompressors have the overload protectors located insidethe shell. A distinctive label on the compressor is used toindicate an internal mounting. Placing a protector insidethe shell has the effect of extending the cooling periodafter an overload trips. Remember, when checking anoverload protector mounted inside, allow the compressorsufficient time to cool so that the protector has a chanceto automatically reset itself. How long is "sufficienttime"? When you can rest your hand comfortably on theshell, the compressor should have cooled enough for youto make a valid test of the overload contacts.

5-6. Check, too, all control switches for properoperation, since one open switch will prevent the unitfrom operating. Such items as thermostats, defrostcontrols, and freezestats are all designed to open andclose the primary circuit. Remember the function of theitem which you are checking, because an open circuitmay not mean that the device is defective. A thermostatshould show an open circuit if the feeler bulb is colderthan its operating point. A defrost control will be open ifthe timer is in the defrost cycle. Some defrost systemshave a reset which is actuated by an increase intemperature above a set point. A freezestat will show anopen circuit when it senses a temperature lower than itsoperating point. You can check the operation of a deviceby raising or lowering its temperature. A thermostat ischecked by placing the feeler bulb in a glass of ice andwater. An ohmmeter or test light is connected across thecontacts so that the time of opening and closing can beobserved. A thermometer is placed in a glass of waterand its temperature is

13

Table 1

read at the time the contacts open. Remove the ice andadd warm water slowly till the contacts close. Again readthe temperature of the water. Replace the thermostat ifit does not conform with manufacturer’s specifications.

5-7. Motor circuit. A hermetic system can bechecked quickly with a motor-start analyzer. It will checkfor continuity in motor windings, for shorted windings,and for grounded windings. It can also be used to start amotor and can reverse the direction of rotation. Theanalyzer contains capacitors which can be used in the

motor circuit to increase its starting torque. Higherstarting torque or momentary reversing are two ways ofunlocking a compressor which for some internal reasoncannot be started normally. When an analyzer is notavailable, plug the refrigerator cord into an outlet and testfor voltage at the terminal block where the cordterminates. There should be voltage at the terminals ifthe cord is good. If the motor runs, you should use aclamp type ammeter to check for correct motor current.Next, you must unplug the cord and make somecontinuity checks with a test light or an ohmmeter.

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Unless you are familiar with the electrical system, youwill need a wiring diagram for the unit which you aretesting.

5-8. Some compressors have an electric heater inthe crankcase to prevent condensing of the refrigerantduring off time. Liquid refrigerant can cause sluggingand damage the compressor. One manufacturer used acapacitor with one of the motor windings to act as aheater during compressor off time. Such a motor wouldalways be "live" even when not running. Be sure of thetype of motor used before you attempt to trace the motorcircuit. Determine the type of relay (hot wire, current, orpotential relay) which is installed in the unit After youhave checked the diagram and understand the circuit, youwill be ready to check out that specific motor.

5-9. For purposes of our explanation, refer tofigure 7, which illustrates the circuit for a potential relay.We will use the compressor motor circuit shown in figure7 to identify the motor's terminals in the followingdiscussion. Make a continuity check from C to S andbetween C and R. A test lamp should light almostnormal in each case if the windings are good. An opencircuit is indicated when the lamp fails to light. Notethat this test is valid only if direct current is used toenergize the circuit. If alternating current is the onlypower available for the test lamp, the commonconnection at C must be opened. Otherwise, the closedcontacts of the relay and the capacitor will make acomplete circuit. Opening C is not necessary whenchecking with an ohmmeter, because it uses directcurrent from self-contained batteries. The reason is thata capacitor blocks direct current while it allows alternatingcurrent to flow. See the paragraph for testing capacitors,where the capacitor is explained more fully.

5-10. To test for a grounded motor winding,check from terminal C to an unpainted part of thecompressor-motor shell. An ohmmeter must be used tomeasure the resistance of the motor windings to test fora shorted coil. Readings should compare closely to thespecifications of the manufacturer. A severely shortedcoil would be indicated by tripping of the branch circuitbreaker or by blowing of the fuse when the unit isplugged into the voltage outlet. If tests indicate that themotor windings are at fault, the hermetic unit must bereplaced.

5-11. If the motor runs but overheats duringoperation, a current draw test with a clamp type ammeterwill give an indication of conditions. Motor currentshould be within 10 percent of nameplate rating on theunit. The nameplate may give two amperage figures,such as FLA 3.5 and LRA 18.0 The FLA stands for "fullload amperage," while LRA stands for "locked rotoramperage.” If the current exceeds the nameplate rating

by more than 10 percent, it is considered unsatisfactory,and the hermetic unit must be replaced. A motordrawing its LRA rating indicates that the rotor is notturning. Conditions inside the sealed unit will also beindicated by unusual vibration and noises. For tests ofthe refrigeration system, see Mechanical Troubles,paragraph 5-17.

5-12. Testing capacitors. We will discuss twomethods for testing a capacitor. When the capacitor canbe disconnected from the circuit and the bleeder resistor,a reasonable test is to charge and then discharge it withits normal voltage (of over 120 v). Charge it bymomentarily applying voltage to its terminals. Then usea piece of insulated wire to short circuit the terminals. Ahot spark indicates that the capacitor is able to hold acharge. Some capacitors have a bleeder resistor ofbetween 15,000 and 30,000 ohms which is in the form ofan integral part that cannot be disconnected. This typeof capacitor may be checked by connecting an ammeterand a 10-, 15-, or 20-amp fuse in series with thecapacitor. Apply 120 volts to the capacitor just longenough to read the ammeter. If the fuse blows, thecapacitor is shorted and must be replaced. Use a fuselarge enough to carry the current and make sure that thecurrent will not be so great as to drive the ammeterneedle off the scale. For example, a 20-mfd capacitor at120 volts should draw less than 1 ampere, while a 400-mfd capacitor at 120 volts will draw 18 amperes. Whenmaking a test, apply voltage to a capacitor just longenough to read the ammeter. The current measuredshould be within 20 percent of that determined by theformula given where mfd is the rating in microfarads andv is the normal applied voltage. The number 2650 is aconstant for 60-cycle current, while 3180 is the constantused when calculating a circuit using 50-cycle current.

A defective capacitor must be replaced by one of thevoltage and mfd rating or the equivalent as specified bythe manufacturer.

5-13. Testing relays. Before testing a relay, youmust know the type. "You may have a schematicdiagram which shows the hookup of the relay but doesnot identify it by name. You should be so familiar withthe common types that you know their characteristicswell enough to identify them. A fan motor is used insome units for forced-air circulation. The diagram infigure 6 shows an example of a relay and a fan motor in

15

the same circuit. The fan motor must be disconnectedbefore testing the relay.

5-14. Referring to figure 5, you will see a type ofhot wire relay that has two bimetal strips, two resistors orheaters, and two set of contacts. Both sets of contactsshould be dosed when the relay is not energized. Thestart contact should open soon as the motor reachesoperating speed. You can verify opening of the startcontacts with a voltmeter which should read line voltageacross the start contacts. A zero reading will indicatethat the contacts are not opening.

5-15. The current relay shown in figure 6 can bechecked for continuity through the coil and for an opencircuit across the contacts when it is not energized. Thecontacts close on starting but should remain open whilethe motor is running. Use direct current, such as with anohmmeter, to test across the relay contacts, as a.c. canfeed around through the motor winding and thecapacitor, giving a false reading of continuity.

5-16. The potential relay, which is shown infigure 7, must be isolated from the compressor motorbefore testing. Open the R and S leads at the terminalson the relay. Check the relay connects between R ad Sfor continuity. The contacts are normally closed; thus,the test should show a complete circuit. A test betweenS and terminal L should also show a complete circuitthrough the coil of the relay. If either test shows anopen circuit, the relay is defective and must be replaced.

5-17. Mechanical Troubles. The mechanicaltroubles found in a refrigerator can be divided into twocategories: (1) those which are caused by defect inmanufacture, and (2) those which are the result ofmishandling or accident. A quick review of mechanicaltroubles is furnished in table 2, where possible causes arelisted with their related faults. As the repair orreplacement of components involves the use of solderingand welding equipment, a review of this subject ispresented before we discus the procedures to follow withspecific items.

6. Braxing, Cutting, and Welding6-1. Before you can join metals or make repairs

you must know how to use welding equipment properly.Safety for yourself is stressed so that you can do thiswork without danger to your self. First, the safety ruleswhich you should know will be presented. Then we willdiscuss the equipment and explain procedures for brazingwith alloys, silver brazing, welding copper, and cuttingmetal.

6-2. Safety Rules. Study the following rules sothat you will understand them. Apply the rules in yourwork so that you will set a good example for others tofollow. You will avoid accidents this way:

• Never drop a cylinder or allow it to fall.

• Never bump a cylinder or otherwise handle itroughly.

• Never lay an acetylene cylinder on its side. Inaddition to acetylene, the tank also contains

infusorial earth, which will get into the regulatorand valves if the tank is placed on its side. Also,safety plugs in the bottom of the tank will passharmlessly into the floor if the cylinder isstanding up when they blow out.

• Never allow oil or grease to come into contactwith oxygen; specifically, never direct a jet ofoxygen at an oil-soaked surface. Spontaneouscombustion may result.

• Never lay an oxygen cylinder on its side. Thetop of the cylinder carries the safety plug. If itblows while the cylinder is on its side, theexhaust pressure released will propel the cylinderlike a rocket.

• Never use oil, grease, or any lubricant on atorch.

• Never hang a torch or hoses on regulators orcylinder valves.

• Never use matches for lighting a torch, as yourhand may be seriously burned as a result. Use afriction igniter or a suitable pilot light.

• Never light the torch from hot metal whenworking in a confined space. Accumulatedfumes can flare or explode.

• Never weld where hot sparks can set fire tomaterial or where sparks can fall on your legs oron the hoses.

• Always wear goggles designed for the weldingwork or brazing which you are doing.

• Never block yourself from the cylinders whenyou are working; make sure that you can get tothem easily and quickly from your workingposition.

• Never store cylinders in direct sunlight or nearheaters.

• A valve clogged with ice may be thawed withwarm water; however, never use a flame orboiling water for this purpose.

• Never test for acetylene leaks with a flamebecause of the danger of a flareback and acylinder fire. Use soapy water, instead.

• Always open valves slowly.

• Always keep the special wrench used to turnacetylene on and off near the valve so that itcan be turned off quickly in an emergency.

• Never hammer or beat on a valve; furthermore,do not attempt to adjust a valve or a gaugewhich does not work.

• Replace protective caps on the cylinderswhenever gauges have been removed.

6-3. Oxygen and Acetylene Apparatus. Infigure 8 you will find an illustration of oxygen andacetylene cylinders and the accessories used with

16

TABLE 2

a soldering and welding torch. The rules for properlysetting up this apparatus are as follows:

• Place the oxygen and acetylene cylinders on alevel floor and secure them so that they cannotbe

• accidentally knocked over. Then remove theprotecting caps.

• Crack each cylinder valve just enough to blowout dirt or foreign matter. Close the valve assoon as the throat is clear, then wipe off theseats. (NOTE: Do not stand in front of a valvewhen cracking it.)

• First, connect the acetylene regulator to theacetylene cylinder; then, second, connect the

oxygen regulator to the oxygen cylinder. Use aclose-fitting wrench to tighten the connectionssufficiently to prevent leakage.

• Connect the red hose to the acetylene regulator.As you do this, note the left-hand threads onthe acetylene hose connections. Next, connectthe green hose to the oxygen regulator. Screwthe connections tight enough to prevent leaking.

• Release the regulator screws to avoid damage tothe regulators and gauges and open the cylindervalves slowly. Read the high-pressure gauge tocheck the pressure of the contents in eachcylinder.

17

Figure 8. Oxygen and acetylene apparatus.

• Blow out the oxygen hose. By turning in theregulator screw; open each regulator (twogauges) so as to blow out the hose; then releasethe regulator screw. If it is necessary to blowout the acetylene hose, you must do the work ina place which is both well ventilated and freefrom sparks or flame.

• Connect the red acetylene hose to the torchneedle valve stamped "AC" and the greenoxygen hose to the torch needle valve stamped"OX." Test all hose connections for leaks at the

torch and at the regulator by turning in bothregulator screws with the torch needle valvesclosed. Release the regulator screws after testingand drain both lines by opening the torch needlevalves.

• Slip the tip nut over the mixing head, screw thetip into the mixing head, and assemble it in thetorch body. Then tighten the assembly by handand adjust the tip to the proper angle. Securethe adjustment by tightening it with the tip-nutwrench.

• Adjust acetylene working pressure by open-

18

TABLE 3

ing the acetylene torch needle valve and turning theregulator screw to the right for the required pressureaccording to the size of the tip. Adjust oxygen workingpressure in the same manner, according to tables 3 and 4.For tip sizes in the low-pressure or injector type of torchuse table 3. For tip sizes in the medium-pressure orbalanced-pressure type of torch, use table 4. (NOTE: Intable 4, each of the first three sizes requires 1 pound ofpressure, while the others take the same number ofpounds of pressure as the tip size. The size of the tipthat you choose is determined by both the thickness ofthe metal or tubing and the area which must be heated.)

6-4. Shutting down the torch safely involves thefollowing 6-step procedure:

• First close the acetylene valve on the torch.• Second, close the oxygen valve on the torch.

• Third, close the acetylene and oxygen cylindervalves.

• Fourth, drain both the regulators and hoses.Open the torch acetylene valve until gas flowstops; then close the valve. Drain the oxygenregulator and hose in the same manner. Boththe high- and low-pressure gauges on the oxygenand acetylene regulators should now read "zero."

• Fifth, release the tension on both regulatorscrews by turning them to the left until theyrotate freely.

• Sixth, coil the hose and suspend it in a suitableholder, being careful to avoid kinking the hose.

6-5. Use of Alloys for Braxing. The alloys usedfor silver brazing all have a melting point above 1000° F.This is, however, still below the melting point of the basemetals to be joined. When properly made, the joint willbe at least strong as the metals joined. You must swageone end of tubing which is to be joined. The swagingtools must be clean and free of oil. This will produce aswaged end which does not require added cleaning. Themost important factor in

TABLE 4

19

joining tubing is to have proper clearance between theparts. An easy slip fit with tubing should approximatethe range .0015 to .005 inch, which is recommended. Toinsure proper centering of the male pat, insert it so as toevenly contact the shoulder of the swaged member. Thisprocedure will insure a uniform distribution of the alloywith no voids and prevent the alloy from dripping intothe inside of the tubing, where it would cause anobstruction. Position the angle of the joint in tubing sothat solder or flux will not drop inside. Rely on capillaryaction to pull the solder throughout the joint.

6-6. The ends of tubing to be joined must besquare and uniformly round. The surfaces must be freeof oil, scale, grease, and dirt. If you find any oil orgrease, you can remove it with hot caustic soda. You canremove scale with an acid pickle bath; however, you mustthen remove all traces of acid after such treatment, sinceany trace of acid left in the tubing will cause trouble inthe future. Avoid handling surfaces after they have beencleaned.

6-7. The alloys listed in table 5 are all suitablefor working with copper, but Easy Flo3, Sil-Fos, andPhos-Copper are considered best. Many manufacturersmake alloys for soldering. Sil-Fos is for use withnonferrous metals only. Pros-Copper will make good joints in copper without flux.Easy-Fo3 is 50 percent silver alloy, with the addition of 3percent nickel. The other Easy-Flo numbers give thepercentage of silver in the alloy. These alloys areavailable from many manufacturers. In using silversolder on fittings, you should be careful to observeinstallation instructions to insure good joints. Onemanufacturer specifies that alloys containing phosphorous,such as Sil-Foe or Silvaloy 15, not be used on fittingswhich are copper-plated steel. They recommend instead,Silvaloy 45 or Easy-Flo.

6-8. It is important that you heat the work to theflow point of the alloy before applying the alloy. Alloyswith a large spread between melting and low point are

easier to work with, since the alloy with a large spreadhas a better chance of making a joint before it sets.

6-9. Use asbestos paper or wet cloth to keep heatfrom pans which might be affected by it. Some valvesare provided with neoprene seats, and these must beremoved if they are too close to where heat will beapplied. Otherwise, the heat will destroy the value of theseat, and the valve will leak.

6-10. When you use flux in making a joint, youshould observe the following: Apply the flux evenly tothe metal surfaces which are to be protected fromoxidation. If the flux wets the surface easily, thisindicates that it is clean. If it balls up and spreadsunevenly, the surface is oily and requires cleaning. Inaddition, the behavior of the flux can be used as atemperature gauge. One popular brand used with brazingbecomes white and puffy about 600° F. A 800° F. itsmoothes out with a milky color, while at 1100° F. itturns clear, and the bright metal surface should showthrough the flux.

6-11. Silver Brazing. This method of joiningmetals is properly called low-temperature brazing, but it isoften incorrectly referred to as silver soldering. It isnecessary to heat the metals only to the melting point ofthe silver solder, 1175° F. A low-melting-point alloy,such as Easy-Flo, is used with a suitable flux, such as thatmade by Handy and Harmon. The melting point of theflux, 1125° F., gives a good indication of when the metalsto be joined are near the correct heat. A carburizing orreducing flame should be used to insure a good pointwhere brazing copper with silver solder. (See fig. 9.)Phos-Copper may be used to join copper to copperwithout using a flux. No flux is an advantage whentubing or parts are joined in a system which should bekept clean. Remember that a clean, dry refrigerationsystem is one that keeps working year after year withoutgiving trouble. A slightly carburizing or reducing flame isrequired when working with Phos-Copper.

6-12. Welding Copper. A welding rod shouldhave approximately the same composition as the

TABLE 5

20

Figure 9. Torch flame.

base metal being handled. Employing such a rod, youmust use a slightly oxidizing flame when you are weldingcopper. Remember, too, that copper will absorb carbonmonoxide gases from a carburizing flame and in a porousweld (since silver solder is worked at a lower temperature,a carburizing flame is used).

6-13. Welding rods, such as Airco 23 DeoxidizedCopper or Oxweld 19 Cupro-Rods, should be suitable for

welding copper. The choice of tip for the torch shouldbe about two sizes larger than that which you wouldchoose for steel of the same gauge. A large flame isrequired because copper conducts heat away much fasterthan steel. No flux is required to make the weld;therefore the weld must be made fast before oxidationoccurs.

6-14. Metal is heated for about 3 inches along theseam to a full red heat. The weld should be startedinside and worked to the nearest edge. The torch shouldbe held at about a 60 angle to the base. Speed should beuniform and the end of the filler rod should be kept inthe molten puddle. During the welding operation, themolten metal is protected by the outer flame envelope.If the metal ceases to flow freely, the filler rod must beraised and the work must again be heated to a full red.

6-15. Cutting Torch. Metal is properly cut with acutting torch which is quite different from the weldingtorch just discussed. However, it is joined to the hoses inthe same manner as the latter, and the same safety rulesapply. The main differences are found in the body ofthe torch and in the tips. Thus, the cutting torch has acompound head which directs a hollow flame ofoxyacetylene. Also, a trigger valve in the body controlsan added jet of oxygen. When the valve is pressed, thisjet of oxygen in the center of the flame makes the cut bysuperheating the metal at the point of contact. A part ofthe cut metal is burned in this operation. Stainless steelis difficult to cut with a torch because it is resistant tooxidation. However stainless steel may be cut by laying asteel welding rod on the cut to be made. The heatdeveloped by oxidation of the rod is sufficient to melt aslot in stainless steel plate. Table 6 gives the pressuresand tip size to use with steel plates of various thickness.The oxygen pressure is set higher to supply the addedoxygen necessary for cutting. Steel is heated toincandescence before the cut is started. As soon as theoxygen jet is applied, the cut will appear at the edge ofthe plate. The cut should be made at a uniform pace asfast as the metal is removed. If the torch is moved tooslow, there will be a waste

TABLE 6

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of both fuel and metal. If the torch is moved too fast,the cut will fail, because the metal is not hot enough.

6-16. Hydrocarbon Torch. Smaller torches whichuse LP gas can be used for silver solder work, but theyare limited to smaller work. They do not produce aslarge a flame, and the temperature of the flame is not ashot as that of the oxyacetylene torch. Otherwise, thesame rules and techniques apply to both kinds of torches.

7. Repairs and Service7-1. Very few refrigerators have service valves or

fittings. You can remedy this by installing an accessoryservice valve or line tap, clamping it to a line where itbecomes a permanent part. A gasket makes a sealbetween the valve and the line, while the valve stem isprovided with a piercing tool which breaks into the line.However because these gaskets leak in time and thevalves are expensive, most shops will maintain a valve kitand a set of adapters. Having such a kit, you can use theadapters to install valves and gauges in a system when itbecomes necessary for you to make pressure tests. Theseadapters, valves, and gauges do not become a permanentpar of the system, and you can remove them aftercompleting the tests. You may also install a gaugemanifold in the system to make tests. The use of agauge manifold is illustrated in Chapter 2, figure 23,where we have described cleaning of the system with acirculator.

7-2. The repair of refrigerators and freezercabinets is generally limited to service and minor repairwork. However, because you may be required to makemore extensive repairs, the explanations are made ascomplete as time and space allows. The material coversleak detecting and repairing, pressure testing, replacing ofa capillary tube, a condenser, a compressor and anevaporator, the cleaning of a system, the removal ofmoisture from a system and the charging of a smallhermetic system.

7-3. Detecting Leaks. When a hermetic systemhas lost some of its charge, you can be sure that there isa leak which must be found and repaired. We willdiscuss here only the two detectors which are mostcommonly employed: the halide and the electronic leakdetectors. But first, several fundamentals should beclarified. Some detectors are so sensitive that they canprove unreliable in air contaminated with a lowconcentration of halogens. In such a situation, thesystem should be charged with nitrogen or carbon dioxideat 60 to 80 p.s.i.g. and checked with a soap solution. Ifa pressure test of the system is also required, follow therecommendations of the American Society ofRefrigeration Engineers as given in the American Codeand explained in paragraph 7-12.

7-4. Halide leak detector. The halide leakdetector (see volume 1) uses bottled gas to heat thereactor plate. A sampling tube is used to pull air and therefrigerant vapor (in case of a leak) into the flame. Totest for leaks, light the torch and let the reactor plate turncherry red, then hold the open end of the rubber tubenear the joint to be tested. A leak is indicated when theflame color changes from blue to blue-green or brightgreen.

7-5. Electronic leak detector. Several companiesproduce electronic detectors which will detect a Freonleak as small as 1/2-ounce per year. The general rules ofoperation for this equipment are as follows:

• Be sure to use the detector with the correctvoltage or the correct batteries. Followinstructions for the detector you are using.

• Allow the unit sufficient time to warm upbefore testing.

• Do not exceed the normal duty cycle if thetester is limited to intermittent duty.

• Keep a record of the hours of operation. Theelement has a limited number of hours of life insome instruments.

• Make correct adjustments for backgroundcontamination. Even after proper adjustment,contaminated air may cause erratic operation ofthe instrument.

• Do not place the detector probe in heavyconcentrations of refrigerant, as it overloads theinstrument.

WARNING: Be sure to observe the warning thatsome instruments carry stating that their use is prohibitedin a combustible or explosive atmosphere.

• Always turn the detector off as soon as you havefinished testing.

7-6. Repairing Leaks. Unless someone haspunched an ice pick through a line, the only place a leakshould occur is at a joint. Before a joint can be soldered,the pressure must be released from the system. Preparethe system as for charging by connecting a "T" and stubinto the suction line. Purge the system to atmosphericpressure. Sweat the joint just as if you were making anew joint, but do not overheat it. Use asbestos paper toprotect adjacent surfaces from the flame. Wrap thetubing with wet cloth where you wish to keep the heatfrom spreading. After you sweat the joint, partiallycharge the system and again test for a leak. If the jointholds, charge the system

22

to its normal capacity and triple pinch the stub to seal it.7-7. Small pinhole leaks in tubing on the low

side of a refrigerator may be repaired in several ways.For example, either cold solder plastics or special resinglues made for refrigeration work may be used to make apatch. At least one resin glue on the market has thesame thermal characteristics as aluminum. A glue likethis will expand and contract with the metal and will notcrack. However, when making a patch with glue, becareful not to force the material through the hole in sucha way as to cause an obstruction in the tubing. Also, thesurface must be kept free of any traces of oil so that theglue will bond properly and completely seal the hole.

7-8. Larger holes in aluminum tubing can berepaired by soldering with 95-5 solder, which can beworked at a lower temperature than that which isrequired for brazing. Here, the right flux to use is just asimportant as the right solder, because flux also has acritical temperature. Some men may be able to usehigher temperature alloys to solder aluminum tubing; butas the work gets hotter, the danger of melting out achunk of material becomes greater.

7-9. Repairs to tubing on the high-pressure sideare made with appropriate solder and flux. The higherpressure in the high side-30 pounds or more-makes itadvisable to repair with hot solder rather than attempt acold glue patch. Remember that the methods we havediscussed here apply to systems using R-12, which includedomestic refrigerators and freezers. If, for example, youshould try to cold patch a leak in a system using R-22,your results would probably be unsatisfactory.Furthermore, the higher operating pressure of R-22-about250 p.s.i.g. requires more strength than can be obtainedby cold patch methods available at the present time.

7-10. Flare connections and fittings. Flareconnections may be provided with seal. These cannot beremoved without tearing them. When opening such aflare connection, cut away the seal with a knife, beingcareful not to nick or scratch the flare. A new seal isinstalled when the flare is reconnected. Always slip theflare nut over the tubing before making a flare. If thenut is too loose, look closely at it size; you may havepicked a nut which is a size too large.

7-11. Flaring. In making a flare, by placing a dropof refrigerant oil on the flaring cone, you can produce asmoother flare. Also, apply refrigerant oil to the nut andthe flare surfaces before assembling them. The oil willallow the flare connection to be drawn up tight withoutoverstraining the nut. It will also lubricate the threads sothat there will be no doubt in your mind as to when thenut is snug.

TABLE 7

7-12. Pressure Testing and Leak Testing withNitrogen or Carbon Dioxide. There may be times whenrefrigerants are not readily available or in short supply.To save refrigerant, you can make pressure checks of asystem using dry nitrogen or CO2. If the pressure test issatisfactory, you can conduct a leak test in two ways.One method calls for charging the system with a smallamount of refrigerant and raising the pressure in thesystem by means of nitrogen. A halide leak detector isthen used to check for leaks. The other method calls forcharging the system to the desired pressure, then testingit for leaks, using a solution of soap and water. Withboth methods the system must be evacuated to bleed offall nitrogen or CO2 after tests are satisfactory and beforecharging with refrigerant.

7-13. Replacing Capillary Tubes. A broken orplugged capillary tube requires a replacement which isexactly the same as the original in its length and insidediameter. Approximately the same length of thereplacement should be soldered to the suction line tomake a heat exchanger. The variations in diameters ofsome capillary tubes are shown in table 7.

7-14. Many refrigerators have a capillary size of .114-inch OD and .049-inch ID when used with R-12. Ofcourse, the outside diameter of each can readily bechecked with a micrometer, while the inside diameter canbe checked with a wire. Notice that both the gauge anddiameter of wire is compared with capillary tubediameters in table 7. Do not try to force a wire into acapillary to check the inside diameter. Also, make certainthat the wire has not been burred on the end as a resultof being crushed by cutters. You can check the diameterof a wire with a wire gauge or a micrometer. In anycase, the correct size wire should slip easily into thecapillary.

7-15. When exact replacements are not available,you may install an adjustable capillary tube in the system.In such an event, the capillary tube should be cut to equalthe length of the one which it replaces. A heatexchanger of the same length is made by soldering thecapillary to the suction line. Note that the ends of thecapillary should be cut with a tube cutter to get a uniformend. Also,

23

swage appropriate ends of the tubing so that the capillarycan be soldered into the system. (NOTE: Keep endstaped or plugged with rubber caps to keep moisture outwhile the system is open.) If fittings are available, thetubing may be quickly joined. However, because suchfittings are expensive, most shops will use a torch andsolder the connections.

7-16. After installation, test the unit for leaks,evacuate it, dry it, charge it with refrigerant, and test it.Set the capillary adjustment so that the evaporator frostsevenly. Then make a final check for proper adjustmentby seeing that the lines to and from the evaporator arenot frosted.

7-17. Replacing the Condenser, Compressor,and Evaporator. Normal service for the condenser,compressor, and evaporator is to clean them with a stiffbristle fiber brush or with compressed air. Thereplacement of these would involve the detailedprocedures just described. Open the system and cap theends with tape or rubber plugs to keep air and moistureout. Then prepare the ends to be soldered and assemblethe system. After that, charge the system and test it forleaks. Next, dry and evacuate the system. Then chargethe system with refrigerant and make an operationalcheck.

7-18. System Cleaning. After a hermetic motorhas burned out, the system will be contaminated withburned pieces of metal and insulation. The dark colorand pungent odor of an oil sample will give muteevidence of such a motor burnout. When it happens,remove the compressor and thoroughly clean the systembefore putting it back into service. As most smaller unitsin this condition should have the entire system replaced,the discussion of cleaning is related in Chapter 2, whereit is most appropriately related to larger systems.

7-19. Removing Moisture. Since acomprehensive explanation of procedures for removingmoisture from both large and small systems is moreappropriate to the equipment discussed in Chapter 2 ofthis volume, it is given there instead of here. Theprocedures described there for systems under 5-toncapacity apply equally well to domestic refrigerators andfreezer cabinets.

7-20. Charging a Small Hermetic. Charging asmall hermetic system with refrigerant is a simpleprocedure which generally requires three steps: (1) dry thesystem, (2) install a suction line stub and a high-pressureline stub, and (3) add the refrigerant. As you know, afew other jobs related to charging must also be done atthe same time. Thus, if the system has a leak, thesystem must be repaired and then tested. The amount ofoil lost can be estimated by the size of the oil spot, whichwill not evaporate. Since most of the oil will remain in

the compressor, the presence of a large amount of oil willindicate a leak in that area. Similarly, if the system hasbeen opened and you suspect that an appreciable amountof moisture has entered it, evacuate the system. Firstcharge the system with a small amount of refrigerant andthen evacuate it to 50 microns (about 29 inches ofvacuum) for from 5 to 30 minutes. Remember, too, thatwhen a system has lost a part of its charge, you shouldassume that some moisture has been drawn into thesystem. To counteract this problem, your first step is toinstall a new drier-strainer.

7-21. Replacing the drier-strainer. The drier-strainer is located between the condenser and thecapillary tube. To replace it, cut the old drier-strainer outof the system and install a new drier-strainer in its place.The new drier will be able to hold the small amount ofmoisture which might have entered the system.

7-22. Installing stubs or process tubes. A systemwhich has no provision for charging and purging musthave stubs installed. To do this, prepare a “T” with abouta 1-foot stub connected to the foot of the "T." Providethe stub with an appropriate fitting and cap the fittinguntil you are ready to use it. The stub and "T" can beheated to insure that they are dry. Cut the suction line ata convenient location and install the “T” and stubpermanently in the line. Also, cut the high-pressure lineat a convenient place and install a "T" and stub there too.Note that some servicemen claim that this is notnecessary if the system is still under pressure. In anyevent, if the stub is connected at the highest part of thecondenser, it will work best for purging air from thesystem.

7-23. Adding refrigerant. When adding refrigerant,first install a valve and a gauge in the high-side stub.Then connect a charging line to the low-side stub. Donot tighten the stub connection until you have purged thecharging line by cracking the refrigerant cylinder valvelong enough to blow out trapped air. Do this by crackingthe valve in the high-side stub and slowly opening thevalve in the charging line. Next, star the compressor andshut the purging valve when refrigerant appears there. Besure to observe any frosting of the evaporator and shutthe charging valve when the coil has become frostedcompletely.

7-24. Continue to observe operation of the unit.High head pressure in excess of 160 p.s.i.g. indicates thatthere is still air in the system which requires purging.Remember that the pressure will vary with the ambienttemperature. Air in the system will also be indicated by alack of uniform warmth of the condenser coil. A checkwith your hand will reveal spots which are cooler nearthe top of the coil, where air pockets are displacing warmliquid. From 15 minutes to half an hour may be requiredto properly charge the system. At

24

the end of this period of observation, check the low sideof the evaporator coil. If the frost line extends too farbeyond the evaporator coil on the suction side, thesystem has been overcharged and some refrigerant shouldbe bled from the system by cracking the valve on thehigh side. If frost shows on the tubing at the inlet (highside), too far from the evaporator coil, increase the sizeof the heat exchanger. Solder another 2 inches of thecapillary to the suction line. This correction would applywhen a new capillary tube has been installed.

7-25. When the performance is satisfactory, closeall of the valves and triple pinch the stubs to seal them.Gauge lines and fittings can then be removed.Remember the necessary steps to prepare a system forservice when moisture is present in it. First, partiallycharge and purge the system of air. Second, pump downto 29 inches of mercury to remove the moisture. Third,install a new drier-strainer. Fourth and fifth, charge thesystem with refrigerant and start the compressor. In thecharging step, no purging of air will be necessary if thesystem has been evacuated. Obviously, pulling a vacuumon the system removes air as well as moisture.

Review ExercisesThe following exercises are study aids. Write your answer

in pencil in the space provided after each exercise. Use theblank pages to record other notes on the chapter content.Immediately check your answers with the key at the end of thetest. Do not submit your answers for grading.

1. What are the main construction features of amodern domestic box? (1-2)

2. Insulation must be able to reduce what threeforms of heat transfer? (1-3)

3. What puts the greatest heat load in arefrigerator? (1-4)

4. What has been the result of using improvedinsulating materials in a refrigerator? (1-5)

5. What must be used with insulation make iteffective in a refrigerator? (1-6)

6. What are some of the big advantages of newsynthetic insulation? (1-6)

7. Why do breaker strips require careful handling?(1-8,9)

8. A stored or abandoned refrigerator should betreated in what way?(1-11)

9. How is the door gasket checked for a seal? (1-12)

10. What factors should you consider in the locationof a refrigerator (1-13)

11. How can you distinguish a refrigerator made foruse overseas? (1-14)

12. An automatic ice maker in a refrigerator may beprovided with two thermostats. What is thefunction of each? (1-18)

13. Why is a second electric heater used in the drainwith an automatic defrost system? (1-20)

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14. Explain a simple automatic defrost system whichuses only one valve for defrosting with hot gas.(1-22)

15. What are the methods of heating used in anabsorption system refrigerator? (2-1)

16. With regard to exercise 15, what is the maindistinction with on fuel? (2-2)

17. Give the principle of operation of the absorptionsystem refrigerator. (2-5)

18. Since the flame burns continuously, how doesthe absorption refrigerator meet changes in heatload? (2-5)

19. After cleaning, what might prevent the burnerfrom operating, and how can this problem besolved successfully? (2-5)

20. Describe the maintenance for a refrigerator withan absorption system. (2-6)

21. How can installation result in poor or faultyoperation of an absorption refrigerator? (2-7)

22. When a refrigerator with an absorption system isplaced in service after an idle period of 6months, it may refuse to cool. How might thisbe corrected? (2-8)

23. Why can a compressor operate so well with suchfine clearances? (3-3)

24. How close may a compressor's piston approachthe head? (3-4)

25. At what point may compressor valves get noisy?(3-5)

26. What advantages do rotary compressors haveover the piston type? (3-6)

27. What is one way of helping to cool thecondenser without having to use a fan? (3-9)

28. A restrictor placed between two sections of anevaporator serves what purpose? (3-10)

29. A weighted valve requires what specialconsideration? (3-11)

30. What are the critical factors in the makeup of acapillary tube? (3-16)

31. Where is a bleeder resistor used and how does itprotect a relay? (3-19)

32. What functions are performed by a hot wirerelay? (3-19)

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33. How does a current relay operate? (3-21)

34. Where would you first check for the cause ofbadly burned relay contacts? (3-24)

35. What does a noisy capillary tube indicate? (3-32)

36. How could low voltage cause excessive electricalconsumption? (3-33)

37. What are the proper methods of manuallydefrosting a freezer? (4-3)

38. What would you suspect if you found heavyfrost had frozen a freezer door shut? (4-4)

39. When troubleshooting, what common fault isoften made by a serviceman? (5-3)

40. State the advantage of locating an overloadprotector inside the compressor's shell. (5-5)

41. What is the difference in operation between athermostat and a freezestat? (5-6)

42. Why is it better to use direct current forchecking a motor circuit? (5-9)

43. What is indicated when a test shows a motordrawing its LRA rating? (5-11)

44. Give two methods for checking a capacitor. (5-12)

45. Describe the main characteristics of a currentrelay. (5-15, also 3-21)

46. Describe the main characteristics of a potentialrelay. (5-16, also 3-24)

47. What are some of the causes of vibration in arefrigerator? (5-17, Table 2)

48. Why must an acetylene cylinder be secured inan upright position? (6-2)

49. Why must an oxygen cylinder be used in anupright position? (6-2)

50. Which is the correct test for an acetylene leak?(6-2)

51. Why must oil and grease be kept away fromoxygen? (6-2)

52. How can you always identify the acetylene valvein a torch? (6-3)

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53. Why must regulator screws be released beforethe cylinder valves are opened? (6-3)

54. In soldering tubing, what is considered the mostimportant factor in making a leakproofconnection? (6-5)

55. How hot should the work be heated before youapply the alloy when you are brazing coopertubing? (6-8)

56. What precautions must be observed when youare brazing certain valves to tubing? (6-9)

57. When you are brazing using a flux, what cluetells you how hot the joint is? (6-10)

58. In view of the last question, how is it that whenyou are brazing copper with silver solder, youshould use a carburizing flame? (6-11)

59. Why must you use a slightly oxidizing flamewhen you are welding copper? (6-12)

60. Why does the welding of copper require a largerflame than that required for welding steel? (6-13)

61. How is a cutting torch used to cut stainlesssteel? (6-15)

62. What are the disadvantages of using a line tap?(7-1)

63. How could a leak detector be too sensitive? (7-3,5)

64. Why should a heavy concentration of halogen beavoided when you are using an electronic leakdetector? (7-5)

65. Where may cold solder or glues be usedsuccessfully for repairs? (7-7)

66. What precautions must be observed when youare patching a hole in tubing? (7-7)

67. Why is it important to use the right flux withthe right solder? (7-8)

68. Cold solder or special glues are limited to whichsystems? (7-9)

69. In what two ways can a system be leak testedwith dry nitrogen? (7-12)

70. What are the most important factors in areplacement capillary tube? (7-13)

71. How can you measure the inside diameter of acapillary tube? (7-14)

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72. What is the purpose of using tape or caps, andwhen are they needed? (7-15, 17)

73. After installation of a major part, what are theproper steps toward placing a system back inservice? (7-16)

74. If you find a very large oil spot, where wouldyou expect to find a leak? (7-20)

75. What would happen if you forgot to purge thecharging line? (7-23)

76. When frost extends out on the suction linebeyond the evaporator coil, what condition isindicated? (7-24)

77. After replacing a capillary tube, you find that thefrost line extends too far on the inlet line orhigh side of the evaporator. What action willcorrect this condition? (7-24)

78. Why must a refrigerator serviceman be able tomake joints like an expert-quickly and correctly?(7-1-24)

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CHAPTER 2

Commercial Refrigeration Systems (Continued)

GRANDPA MAY HAVE had problems with his oldice box, but the problems of his neighborhood grocertrying to keep meats and vegetables fresh were muchgreater. His corner druggist also had trouble keeping theice cream hard and had to keep a cold drink chilled withice. By way of contrast, today's grocer has large storagecabinets which are automatically cooled, and the present-day druggist has refrigerated cases which keep ice creamhard and cold drinks really cold. In addition, many storesnow have water coolers for the comfort of theircustomers.

2. Continuing the discussion which we began inChapter 1, we will now explain different applications ofcompressors for water and beverage coolers, for icemaking machines (such as ice cube makers and flake icemachines), and for soda fountains. Other applicationswhich we will discuss are those involving storage cabinets(such as reach-in, walk-in, and display cabinets) and thedefrosting for such cabinets. (Of course, these largersystems may use a hermetic unit, such as we havediscussed in Chapter 1 in reference to refrigerators andfreezers. ) You will find the open type compressordiscussed in Section 13, under the heading "SystemComponents." Similarly, you will find system cleaningexplained (under the same name) in Section 17. Thetroubleshooting and repair sections are a continuationfrom the preceding chapter.

8. Water Coolers8-1. Package units for cool drinking water are used in

offices, shops, and messhalls. They are rated in gallonsof water cooled per hour, with capacities ranging from 3to 20 gallons per hour. The control of each is adjusted tosupply water at a temperature of 50° F. These rangefrom the bottle type through the bubbler type to theremote unit multiple type. All, of course, developtroubles which require servicing or repairing.

8-2. Bottle Type. The bottle type water cooler isinstalled where drinking water connections are not readilyavailable. A freezestat is employed in the control circuit

with the thermostat to insure against ice damage to thetank. The thermostat is set so that a thin coat of ice willform on the coils before the compressor is stopped. Thefreezestat opens the control circuit before ice formationdamages the tank if the thermostat should fail to stop thecompressor. The schematic diagram shown in figure 6,Chapter 1, is typical of the control circuit using a currentrelay for a unit type water cooler. The majorcomponents in such a water cooler are the same as in asimple refrigerator.

8-3. Bubbler Type. The bubbler type water coolerhas a tap water inlet connecting to the water service lineand a drain outlet connecting to the waste system. Theunit may be designed to take advantage of cold wastewater in a bubbler fountain by using a precooler.Typically, the warm water coming into the unit firstpasses through a coil which wraps around the drain sump.Then the water passes into an accumulator tank, wherethe evaporator coil is located. The design is calculated tocool the unit enough to produce a small amount of ice inthe tank. This procedure thereby assures a reservecarryover during compressor off time.

8-4. Remote Unit Multiple Type. You will find theremote unit multiple type water cooler in a large modemhospital or office building. A compressor unit of therequired size will be located at some remote place in thebuilding. It may be a hermetic unit, but if the heat loadis great enough, an open type compressor may beinstalled. From the heat exchanger at the remotelocation, insulated pipes carry the cold water to bubblerfountains and other outlets throughout the building Alarge installation may require a 10-ton unit to insure anadequate supply of cold water in hot weather.

8-5. Troubleshooting. Troubleshooting proceduresare the same as those described for the hermetic unit in arefrigerator, with these additions. You may be called toservice a unit which has a faulty valve or a plugged drain.One of the troubles with a valve is a slip in the linkage ofthe foot pedal which requires readjustment and lock-

80

ing. Another trouble is salt formation in the valve.Disassembly and cleaning of the seat and washer willsolve the latter problem in most cases. However, youmust replace the washer if it is grooved or warped. Also,a plugged drain requires disassembly and cleaning,whereas a leaking water tank or line may be repaired witha plastic or synthetic glue, provided it is not toxic and notpoisonous.

9. Beverage Coolers9-1. There are some persons who would have you

believe that beverage coolers are a "big deal." However,there is nothing mysterious about them. Their purpose isto cool bottled beverages in the range of 27° to 40° F.,depending on the freezing point of the liquid. Thecooling system is designed to meet the following factors:

• Anticipated heat load.• Freeing point of beverage.• Desired temperature of beverage.

9-2. If a box isloaded with a different beverage from that for which itwas designed, it may be necessary to change the "coldsetting" to prevent freezing the product. The position ofthe feeler bulb and the thermostat setting determine whatrange of temperature a box will hold.

9-3. A self-contained unit of the horizontal type will use a hermeticsystem layout similar to that of a freezer chest, whereas avertical unit will have a layout like that of a refrigerator.A heavy duty hermetic unit will be provided with an oilpump and an oil cooler. The condenser shown in figure10 illustrates a heavy duty type which includes a coil forthe oil cooler. The oil cooler coil will normally be hotterthan the condenser. The larger display type beveragecooler has a remote compressor and condenser located ina compressor room or in an outside shed. The onemajor difference between a horizontal and an uprightcase lies in the style and layout of the evaporator. Thehorizontal case will have a wall type evaporator, while theupright case will use a plate type with forced air. Repairsand service for a hermetic system are the same as thosewhich you studied for a refrigerator. Remotecompressors of the open type are explained in Section 13.

10. Ice Making Machines10-1. Several types

of machines are manufactured for making ice cubes orflakes. For example, one type of automatic ice cubemaker has already been explained in our discussion ofdomestic refrigerators. Ice cube makers are classedaccording to the evaporator as of the tray type, the tubetype, the cell type, or the plate type. In comparison,machines for making ice flakes are classed as of the platetype, the rotating cylinder type, and the flexiblemembrane type. These latter machines

Figure 10. Condenser coil with oil cooler

all have the same purpose, but they employ differenttypes of evaporators.

10-2.Components. Whatever the type, the parts ordinarilyfound in most icemaking machines are a hermeticcompressor; a condenser cooled by air, water, or acombination of both; and a receiver-drier-strainer. Therefrigerant control can be a capillary tube, a constant-pressure expansion valve, or a thermostatic expansionvalve. Of these, a system using a thermostatic expansionvalve will require a receiver. Where evaporator heat isused to loosen the ice, you will find a hot gas solenoidvalve. The water-handling system will be continuousflow or intermittent. Also, the control of the ice formingand harvest cycle will be on a continuous basis in therotating cylinder type, with the starting and stopping ofthe unit being the main control function. An automatictray type will follow a cycle which is timed in the mannerwhich we have already described for an automatic icecube maker in a refrigerator.

10-3. Ice CubeEvaporators. The biggest difference found among icemaking machines lies in the evaporator used. Becausethe tray type evaporator has already been described, itshould give you no difficulty. Since the main differenceamong

31

such machines lies in the method of ejecting the cubesfrom the tray, we will not discuss it here; tube typeevaporators will be taken up first instead.

10-4. Tube typesevaporators. This arrangement has the evaporator form abank of tubes. Water flows down the inside of the tubeand is frozen. As more ice is formed, the hole in thecenter becomes smaller and restricts the flow of wateruntil finally the excess water triggers the harvest cycle. Ahot gas solenoid valve operates to allow the evaporator torelease the ice. In one machine the long rods are cutinto suitable lengths. In another machine, the evaporatortubes are chilled in sections so that rods of the desiredlength are formed between the warm spots. Still anothermethod uses accumulated water pressure to eject the icerod with enough force to break it.

10-5. Cell typeevaporator. There are two major variations of the celltype evaporator. In one the cell operates under water,and when the ice is released it floats to the surface whereit is forced from the tank by a current of water. In theother type, inverted cells are used which have watersprayed against them. The ice forming period is set by atimer, which then frees the ice by hot gas.

10-6. Plate typeevaporators. Among the variations of the flat plate type,there is one main distinction: the plate may be eitherhorizontal or vertical. For instance, in one type ofmachine, the horizontal plate produces a slab of ice,which is then moved on to a hot wire grid which isheated electrically. Here the slab melts into individualcubes, which then fall through into a storage bin.

10-7. Another typeof such a machine uses a grid which is moved intoposition against a vertical plate. After the cube isformed, the grid is moved against a knockout plate whichejects the cubes. In one design, two vertical plates havematching cold spots which face each other. A uniquefeature of this model is a variable control over the lengthof the period for forming ice. Within a short period, theice produced will be like a lens. If the period is longenough, the two opposite lenses will build a bridge toeach other and produce a piece of ice which looks like aYo-Yo.

10-8. Blowdown.Units are provided with a siphon the water pan to blowdown the water system each time the unit stops. Acomplete flush removes the accumulated salts. The waterleft behind from each freezing cycle concentrates thesalts in the water. Where the water is very hard, amanual blowdown may be necessary to move the salt andinsure proper formation of ice.

10-9. Flake IceMachines. These units use some evaporators which aresimilar to those of the cube makers, but the harvestingmethod employed is different.

10-10. Plate typeevaporator. In this type of evaporator a thin sheet of iceis formed on the plate. When the desired thickness isreached, hot gas is directed to the plate to loosen the ice,which then passes through a crusher or grinder. Anotherarrangement freezes the slab in a spring-metal grid.After it is free of the plate, the flexible grid is drawn overa sharp bend, causing the ice to fracture into small pieces.A variation of this last method uses a flexible belt ormembrane which passes over a plate or a refrigeratedroller. The belt breaks up its cargo by passing around asharp bend.

10-11. Cylinder typeevaporator. Again, in this type, there are many variations,but the essential items are the refrigerated cylinder and acutter-scraper for harvesting. Water may be flowed orsprayed on the cylinder continuously. Harvesting occurswhen the ice becomes thick enough to contact thecutters. The machine will continue to make ice until alevel is reached in the storage bin, where the ice contactsa feeler which, in turn, will stop the machine. Theoperation of the feeler is the same as that in the storagebin of an automatic cube maker. The position of thefeeler determines the amount of ice which will be storedin the bin before the machine is stopped.

10-12. Troubles inIce Makers. With so many different types of icemakingmachines being used, you will find that it is necessary tohave the right service manual for the equipment on handwhen you are dealing with mechanical trouble or neededadjustments. You will find, too, that after mechanicalproblems, the water supply is probably the next greatestsource of trouble. Sediment, scale, and salt formation areproblems which vary widely from one locality to another.In fact, under severe conditions, water treatment may bethe only means of keeping an automatic ice maker insatisfactory operation. On the other hand, in somelocalities, the domestic water supply contains so much saltthat crystals lodge in the seat of a faucet, causing it todrip. Thus, such faucets in everyday use require thatincrustation be removed from the stem and gasket every2 or 3 months.

11. Soda Fountains11-1. A recent

addition to your responsibilities is the maintenance ofsoda fountains. A complete fountain has an ice creamcompartment, cold bottle storage, syrup cooler, and abeverage cooler. Among other things, we will discuss adry type eat exchanger coil aid a carbonator system. Atypical soda fountain is shown in figure 11, with onecompressor attached to a multiple evaporator. The syrupsand the drinking water are kept at 45° to 50° F, while theice cream compartment is held between 0° and 10° F.The heat exchanger, at the left in figure 11, serves tocool the liquid

32

Figure 11. A typical soda fountain.

refrigerant so it can absorb more latent heat as it changesto a gas. As you know, a lower refrigerant temperaturealso reduces the tendency of the liquid to ash to a gas asit passes the control valve. Flashing at the valve reducesthe valve's capacity and also reduces the efficiency of thesystem.

11-2. Dry TypeCoil. The beverage cooler, shown at the right in figure11, is a dry type heat exchanger. It consists of analuminum casting which contains at least two sets ofcoils. Additional coils are provided when more than onebeverage is to be cooled. One coil is an evaporator, andthe other coil (or coils) carries the liquid to be cooled. Aheat exchanger of this type must be large enough to meetthe cooling demands of the system. At the same time, itmust provide sufficient transfer of heat so that it doesnot increase the pressure drop in the low side too much.To prevent this condition, a suction pressure regulatingvalve may be placed in the suction line from the heatexchanger. A component which is often part of a sodafountain is the carbonator which makes soda water.

11-3. CarbonatorSystem. The carbonator which is included in some sodafountains is not as complicated as some people suppose.

With the information which follows, you should be ableto maintain a carbonator in satisfactory operation. It hasfour essential parts: a CO2 tank, a mixing tank, a waterpump, and an electrical control to operate the waterpump. The CO2 tank is used to charge the mixing tankwith gas at 80 p.s.i.g. The correct pressure is adjusted bymeans of a pressure regulating valve. The water pump isused to deliver a high-velocity jet into the mixing tank.The turbulence is so great that the water readily absorbsseveral times its own volume of CO2. The water fromthe pump should be chilled before it enters the mixingtank, since cold water absorbs CO2 much more readilythan warm tap water. The mixing tank is alsorefrigerated to ensure delivery of cold soda at the valve,because warm soda water loses its charge very quickly.Carbonated water is drawn from the bottom of the tankbelow a baffle, which keeps turbulence from this area.

11-4. The pumpmotor is started and stopped by a magnetic contactorwhich is controlled by a float or by an electrode circuit inthe tank. Operation of an electrode circuit is illustratedin figure 12. However, the CO2 tank and chargingconnections are not shown. The transformer serves toisolate the control circuit from the house electricalservice. Of course, the tank ground and the trans-

33

Figure 12. Carbonator pump motor control.

former secondary ground need not be connected to eachother if both connections are made to a cold water pipe.The figure shows the position of the switch contacts withthe pump running and the tank being filled with water.When the water level reaches the upper electrode, acircuit is completed for the holding coil by way of thewater and the ground path. This energizes the holdingcoil, which pulls the armature down and opens the circuitto the pump motor. At the same time, another pair ofcontacts close a circuit to keep the holding coil energizedby way of the bottom electrode. The pump motor willstart again when water drops below the lower electrode,because then the holding coil will no longer be energizedand the spring will pull the armature up, closing thecircuit to the pump motor.

12. Storage Cabinets12-1 The types of

cabinets which you will find used at military installationsare reach-in, walk-

TABLE 8

in, and display cabinets. The temperature range forstorage of different foods is shown in table 8. From theinformation in this table, you can see that a displaycabinet designed for fresh meats would not have thecooling capacity for frozen foods. Thus, while twocabinets may appear to be similar, they may be quitedifferent in design and performance. Defrostingproblems related to these cabinets are also discussed laterin this section.

12-2. Reach-InCabinets. This type of cabinet is familiar to many of usas the self-service refrigerator used for dairy products atthe neighborhood grocery store. In appearance it lookslike an oversize refrigerator with glass doors. If it useswooden shelves, they must be made of spruce or maple,as these woods have no appreciable odor. The largersizes of such cabinets may have as much as 100 cubicfeet capacity. Either self-contained or remote condensingunits are available. Evaporators are forced air or naturalconvection, depending on the purpose of the cabinet Amodern reach-in cabinet for a messhall has forced-aircirculation and automatic defrosting. The defrost cycle isdesigned so that the unit will give frost-free operation.However, manual defrosting is necessary when theequipment is subjected to such adverse conditions asoperation in a highly humid atmosphere. Remember,too, that reach-in cabinets used for low-temperatureservice will accumulate frost at a much higher rate thanthose operated at temperatures above freeing.

12-3. Walk-InCabinets. These are used to provide temporary coldstorage of food in messhalls and commissaries. A largeconsolidated

34

messhall has three walk-ins operated at temperaturesappropriate to the food held in them. Older models usehot water defrost in which the unit is turned off andwater is flushed over the evaporator coils until the frost iswashed off. Since evaporators are of the forced-air type,the unit must be shut off before defrosting to preventwater being blown all over the cabinet. Late modelcabinets have automatic defrosting controlled by anelectric clock; they use the hot gas method. Thecompressors for these cabinets are mounted in a shedoutside in mild climates. However, a compressor room ispreferred in cold climates to insure operation of allcompressors.

12-4. For manyyears wooden cabinets with cork-fill insulation werestandard for walk-ins. In contrast, new constructionmethods now use metal panels with porcelain or enamelfinish for the cabinet. This change has led to moresanitary conditions and easier maintenance. This isespecially true since some synthetic insulating materialsare as good as cork. In fact, if production costs drop lowenough, these synthetics may replace cork. Unlikeorganic materials, synthetics are vermin-proof and are notreadily susceptible to fungus when moisture gets past theseal. The application of modern insulation is explained indetail in Chapter 3, Cold Storage and Ice Plants.

12-5. DisplayCabinets. These are known as open or closed and single-or double-duty cabinets. In the double-duty case, boththe display section and the base section are refrigerated.The type of food to be stored will determine operatingtemperature of the case and the design of the evaporator.The evaporator may be of either the plate type or afinned tube with forced-air circulation. Sections may bejoined together to make a cabinet of any desired length.A cabinet made of several sections will usually have amultiple evaporator system, such as we will discuss inChapter 4.

12-6. Displaycabinets are constructed of steel panels with bakedenamel and porcelain finishes. Corkboard, glass wool, orsynthetics may be used for insulation. In some type ofconstruction, certain parts may rely on formed insulationfor some of the strength and rigidity of the cabinet. Theinsulation may be blanket type, batts, panel, or formedmember. Electric heater strips are provided around doorsor access openings to prevent frost which could freeze adoor shut.

12-7. Open typedisplay cabinets are successful because of thedevelopment of the air curtain which keeps heat gain at aminimum. Careful design of the forced-air system hasled to an ideal combination of fans and ducts to producea curtain of cold air. Anything which interferes ordisrupts the flow of air would result in excessiveoperation of the compressor. Thus, the open type display

case must be in an air-conditioned space for satisfactoryoperation. Otherwise, the unit will accumulate frost at anabnormal rate so that manual defrosting is required. Thislatter is necessary because the frost layer disrupts the aircurrent when the frost gets too thick and must beremoved by manual means, such as flooding with hotwater. However, the defrosting methods which wediscuss next will function properly if the cabinet is usedin an area which is air conditioned.

12-8. DefrostingMethods. The methods for defrosting storage cabinetsare (1) compressor off time, (2) hot gas, (3) hot wire, (4)hot water, and (5) secondary solution. If you arestationed at an older base where equipment has beenpurchased over a long period of years, you may find all ofthese defrost methods being used.

12-9. Compressoroff time. The compressor off-time method is limited tocabinets operating at temperatures above 28°. Ambienttemperature is relied on to bring the evaporator coiltemperature up to where the frost will melt.

12-10. Off-timedefrost may be controlled (1) by suction pressure, (2) bytime clock, or (3) by a combination, with a time clockused to start the cycle. The first, suction pressurecontrol, has two disadvantages which affect operation ofthe unit. For one thing, under an increased heat load, iceforming on the evaporator will cause the unit to stop fora defrost period. Another drawback is found in coldweather, when low outdoor temperature can make thecompressor cooler than the evaporator. Under thiscondition the suction pressure can remain below the cut-in point and the unit will remain idle. This last conditionwould occur in a normally mild climate when a coldwave has sent temperatures to below freezing level. Thesecond control method, time clock control defrost, isindependent of temperature variations when it has boththe start and terminate function. However, when timerstart is combined with suction pressure termination., youcan expect to find the difficulty we have just described.

12-11. Hot gasdefrosting. When this method is used for large displaycabinets, it requires some modification from the simplesystem that we have explained for a domesticrefrigerator. One disadvantage (among many) of thissystem is that in cold weather the compressor may notdeliver enough heat for the rapid defrosting which isexpected from a modem unit. Consequently, a numberof variations of the simple system are used to overcomethe disadvantages as follows: (1) Meter the hot gas to theevaporator so as to prevent formation of liquid whichcould get back to the compressor. (Just a small amountof liquid entering the compressor will cause pistons tohammer.) (2) Use a liquid receiver and meter the liquidinto the suction line. (3) Add sufficient heat to insurethat the refrigerant will be a gas

35

when it returns to the compressor. (4) Use a four-wayvalve in the system to completely reverse it so that theevaporator functions as a condenser and the condenserserves as an evaporator during the defrost cycle. Theobvious disadvantage to avoid here is that hot gas candefrost the coils so rapidly that the drain lines mayrequire heating to prevent melted water from freezing inthe drains and plugging them.

12-12. Hot wiredefrosting. This method has the big advantage of beingunaffected by changes in ambient temperature. Theheater wire may be laid in contact with the evaporator, orit may be hung in the form of a grid between theevaporator and the fan when forced-air circulation isused. A fan switch is a necessary part of the automaticdefrost system where the forced-air may drive meltedwater out of the drains. The hot wire defrost cycle is soshort that the drains require heating to prevent freezeup.Improved electrical heating elements account for thespeed, because heating is almost instantaneous throughthe whole evaporator.

12-13. Hot waterspray. Defrosting with hot water uses a water bath orspray aimed directly on to the evaporator. This systemrequires that the compressor and air circulation fan beshut off before the water is turned on. The cycle mustbe long enough to insure drainage of water from theevaporator before the unit is restarted.

12-14. Secondarysolution. This method of defrosting uses a refrigerantwhich is heated and passed through a secondary coil inthe evaporator. You should recognize that this system issimilar to hot wire defrosting in that it will not beaffected by changes in ambient temperature. It appearsthat at the present time the secondary solution methodhas generally been replaced by the hot wire system.

12-15. High-temperature control. Safety controls are an important partof automatic defrosting systems applied to largecommercial cabinets. You will find that a high-temperature control is used to terminate the defrost cycle,thereby preventing the cabinet temperature from goingtoo high and thus endangering the food in storage. Thisis an added safety feature which will take over if thedefrost cycle should be interrupted and fail to completeitself.

12-16. High-pressurecontrol. A system which uses hot gas defrosting mayhave a pressure cutout switch to keep the unit fromoperating at too high a pressure. The defrost valve willhave an auxiliary outlet connected by capillary tubing tothe pressure control. When the defrost valve is open, itsupplies pressure to a bellows in the pressure control..The pressure control is set to open at 180 pounds andclose at 155 when it is used on a system charged with R-

12. The contacts in the pressure control will open thecompressor motor circuit if pressure exceeds its setting.

13. System Components13-1. In the last

section we discussed cabinets which are often made inlarge sizes. A walk-in cabinet for milk products handledat a big commissary store may require enough capacity tocool a room 20 by 40 feet. The refrigerant flow in sucha system is shown in figure 13. The valves andaccessories of the system are discussed in this section.

13-2. Open TypeCompressors. So far, we have discussed the hermeticcompressor, which, normally, you will not be able torepair. The welded case of a hermetic unit is beyond thecapability of the repair shop. However, a semi-hermeticunit has a bolted case which can be disassembled tomake repairs to the compressor. The one big differenceis that a semi-hermetic does not require the shaft sealwhich an open type compressor must have. If you havenot had the opportunity of working with a larger system,you will probably benefit greatly from a review of themajor components. The following discussion is related tothe items illustrated in figure 13, which shows a lowdiagram of a refrigeration system.

13-3. Separator.The oil separator is a simple trap designed to remove theoil from the hot refrigerant gas and return the oil to thecompressor. A float is used to open a valve which allowsthe accumulated oil to return to the sump.

13-4. ServiceValves. The suction service and the discharge servicevalves are provided with fittings so that they may beconnected to gauges and to charging lines. The valvesalso serve to isolate the compressor from the system if itis necessary to replace the compressor unit.

13-5. Condensers.Several types of condensers may be found with largeinstallations. The choice is dictated by the cooling loadof the unit and the weather factors of the locality.

13-6. Air-cooledcondensers. This condenser is the most simple type andgives the least amount of trouble. For heavy duty, thecondenser is enclosed in a shroud, and a fan forces airacross the coils to cool them.

13-7. Water-cooledcondenser. Water-cooled condensers are of the shell-and-tube type or the tube-within-a-tube type. In the first type,water circulates through the tubing while the shell servesas both condenser and receiver. In contrast, the double-tube type circulates the refrigerant through the outer tubeto take advantage of the air cooling the refrigerant.When a compressor is also water cooled, the exhaustwater from the condenser is circulated on through thecylinder heads. Where water is at a premium, a spraypond or cooling

36

Figure 13. Flow schematic of refrigeration system.

tower is used to cool the water so that it can be usedover again.

13-8. Receivers.The receiver in a system must be large enough so that itcan hold all of the refrigerant in the system. Thereceiver is the tank where the refrigerant is stored after asystem is pumped down. The receiver outlet valve is aquill type, with its inlet tube (quill) reaching to thebottom of the receiver. It is referred to as a king valve,because this is the valve which is closed while a system isbeing pumped down. The receiver inlet valve is closedafter pumping down is completed.

13-9. Drier-Strainer. The drier-strainer is a cartridge type withdirection flow indication on the case. Direction flowmust be observed as it is arranged so that the strainer willhold particles of drier which might be dislodged. Also,the unit is properly baffled for liquid flow in the directionindicated.

13-10. Sight Glass.The sight glass enables you to see the flow of refrigerantin the system. Bubbles will appear when the charge getslow; they indicate that the system is losing refrigerant.

13-11. RefrigerantControls. The principles of refrigerant control are thesame for valves as for capillary tubes. However, valvesprovide a variable control over a wider range of load.Modern valves are designed so as to modulate refrigerantflow to meet variations in load. The valve must notstarve the evaporator; this is not good economy.Likewise, the valve must not cause flooding, since thiscan damage the compressor. As you study these valves,see if you can find examples of the types mentioned herewhich are present in the equipment used at yourinstallation. NOTE: Although figure 13 illustrates anautomatic expansion

37

valve, such as is covered first below, other types of valvesare also discussed including thermostatic expansionvalves, high-side float valves, and low-side float valves.

13-12. Automaticexpansion valves. The first valves to be developed asautomatic were known as the constant-pressure type.The automatic expansion valve has a spring on each sideof a diaphragm. Evaporator pressure under thediaphragm acts with the closing spring to close the valvewhen the pressure rises. This kind of valve has beenused in systems with ammonia. It does not modulate, soit is not used as a refrigerant control where the loadchange is great. One quite common application of theautomatic expansion valve is in drinking water coolers,because their heat load is fairly constant in a narrowtemperature range. The automatic constant-pressureexpansion valve has also been used successfully as a pilotvalve for larger valves. One such application is for thecontrol of a suction pressure regulator. As a pilot, theautomatic expansion valve may even be used to operate asuction service stop valve to prevent freezing. Anequalizer line is used to compensate for the pressure dropacross the valve.

13-13. Thermostaticexpansion valves. Valves of this type use a bulb andcapillary tube to transmit pressure to a spring-loadedbellows or diaphragm. Such valves are identified by (1)the size of connections, (2) the length of the capillary, (3)the internal or external equalizer connection, (4) thecapacity, and (5) the type of refrigerant charge. The typeof charge is indicated by the color used on a valveaccording to the following list:

Refrigerant Color12 yellow22 green

500 orange502 orchid40 red

717 whiteThe capacity is the nominal capacity of the valve in tonsof refrigeration. There are three kinds of refrigerantcharge used in thermostatic expansion valves: liquidcharge, gas charge, and cross charge.

a. Liquid charge. This valve has the remote bulband capillary charged with the same refrigerant (R-12 forexample) as that which is used in the system with whichthe valve is to be used. The liquid charge is sufficient sothat some liquid will be left in the bulb under allconditions. The advantage of such a charge is that it willcontrol the refrigerant even when the valve or diaphragmis colder than the bulb. Among the disadvantages ofsuch a charge are possible flooding and hunting. Its mainapplication is found in low-temperature systems of largecapacity.

b. Gas charge. This valve has the bulb andcapillary charged with the same refrigerant as that presentin the system with which it is to be used However, theamount of the charge employed is smaller than thatfound in the liquid charge; thus at a predetermined point,all of the liquid will become vapor. This point is themaximum operating pressure of the valve. Thedisadvantage of such a charge is that the control will belost if the diaphragm and case are colder than the bulb,since refrigerant will then condense in the valve. For thisreason the application is only suitable to a system whichoperates at temperatures above freezing and where theevaporator pressure drop insures that bulb temperatureswill be colder.

c. Cross charge. The cross charge expansion valveuses a liquid charge in the bulb and capillary which isdifferent from the refrigerant found in the system withwhich it is used. The pressure-temperature curve of thecharge is such that it will cross the pressure-temperaturecurve of the refrigerant used in the system. By carefulselection of the refrigerant used for the cross charge, themanufacturer can make a valve which will perform bestin any desired range or for any set of conditions. Someof the advantages of such a charge are these: (1) thevalve closes quickly when the compressor stops; (2) thevalve exercises control at high suction temperature,preventing floodback; and (3) the valve is more sensitiveto pressure changes rather than bulb temperature changes,which reduce hunting.13-14. High-side float valves. This control is normally

used with a single evaporator, but it can control severalevaporators if they are connected in series and if each isprovided with an individual bypass. The high-pressurefloat valve, used with a flooded evaporator, has twoadvantages: First, all of the refrigerant is liquid when itenters the evaporator, so there is no cooling lost fromexpansion taking place in the delivery line. Second, all ofthe refrigerant passing through the valve is liquid, so thecapacity of the valve is not subjected to changes fromflashing. The evaporator may be a bunker type withforced-air circulation or a shell-and-tube type for brinewater chilling. A surge drum is installed at theevaporator to prevent flooding of the compressor duringchanges in load. The amount of refrigerant charge iscritical, for if the system is charged beyond its capacity,flooding will damage the compressor. The evaporator isprovided with an oil drain and return line to thecompressor.13-15. Low-side float valves. Such valves are each

connected into the low-pressure side of the system, butthe function of this valve is almost the same as that ofthe high-side float valve. The difference is that a part ofthe evaporator space is taken up by the tank and floatcontrol. Adjust-

38

ment of the low-side float is critical. If the refrigerantlevel is too low, oil may accumulate in the float chamber,leaving the compressor with insufficient oil to lubricate it.Another effect of the layer of oil on top of therefrigerant is that it may cause the refrigerant to refuse toboil until a much lower temperature-pressure point isreached. Ebullators are used as catalysts to insure boilingof the refrigerant at its normal point.13-16. Compressor Pressure Switch. In figure 13 you

will find that item 12 is a switch with capillary lines tothe high side and low side of the compressor. In such asituation, a combination switch can be used in manyways. One application would be as a high-pressure andlow-pressure safety switch. Another application would beas a high-pressure safety switch and low-pressure motorcontrol. Specific functions are, of course, determined bythe system involved and the purpose intended.

14. Troubleshooting and Repairs14-1. When a service call is received, it usually means

trouble. If you were the boss and had a choice, whowould you send? Would you choose the mostexperienced man, the one best able to do the job quickly?But what about the man with little experience? He needsthe opportunity to learn. The solution is to, perhaps,send the inexperienced man along as a helper. As you dothis, you can make sure that the challenging jobs will goto the better qualified, while the simpler jobs will go tothe less qualified. After all, whether you are in militaryor civilian life, it is usually the best qualified man whogets the most pay and the most interesting assignments,isn't it? In this section we will discuss many problemsyou would encounter in troubleshooting the largersystems which use an open type compressor. Then, inSections 15, 16, 17, and 18, we will take up severalaspects of servicing, each of which is important enoughin itself to be studied separately rather than as subparts ofservicing. But first, let us consider the basic rules ofelectrical safety which you must know in order to avoidgetting into trouble.

14-2. Electrical Safety. In spite of repeated warningsmany servicemen forget the safety rules and becomeinvolved with a live circuit. Then they learn the hardway-perhaps even fatally-that memorizing the safety rulesis not enough; these rules must be practiced-consistently,automatically! Briefly they are:

• Do not wear rings or metal watchbands at work.

• Treat all circuits as live circuits unless you knowthey are dead.

• Be sure switches are of and tagged beforeworking on a circuit.

• Do not wear shoes with metal clips or hobnails.• No horseplay. Distractions cause accidents.

• When testing or working on a live circuit, usethe buddy system. A loner may lose his life.

Remember, the man who practices safety will develophabit patterns which will protect him. Then -having suchhabits-such a man can devote more of his attention tothe particular problem he is trying to solve.

14-3. Electrical Troubles. Let us discuss normaloperation first. For a brief review of electricity, considerwhat a circuit does: Something happens when a circuit iscompleted. Something happens when a circuit is opened.Keep these two things in mind when you are looking fora trouble, and the solution will be easier to find.Actually, you are looking for the answers to a series ofunspoken questions. Yet, their answers will becomemore obvious if you will state the questions to yourself.For example, "Why doesn't the compressor motor start?"Answer! "An open circuit!" "Where?" This is what youare really seeking. "Where is the open circuit?" Here areyour six possible answers:

• At the circuit breaker or fuse box.• At the motor starter.• At the control switch.• At one of the safety or lockout switches.

• At an open connection or a loose terminal(which may be one and the same thing).

• At a broken wire.14-4. Electrical Repairs. Several specific

remedies are available, depending on where a fault islocated. To name a few: (1) At a circuit breaker, pressingthe "Reset" button will restore the circuit if it has openedbecause of overload. (2) A blown fuse calls for areplacement of the same size. (3) A loose terminal canbe tightened. (4) A broken wire can be spliced, soldered,and then insulated with electricians' tape.

14-5. When several safety controls are used inone circuit, they are connected in series with each other.The operation of any one of the safety control devicesopens the circuit. When more than one control switch isused to complete the circuit to a motor from differentlocations the control switches must be connected inparallel. Thus, you must know the purpose and functionof a control before you start to troubleshoot it.

14-6. Three-phase motors are preferred in unitslarger than 5 horsepower. Tests on a three-phase motorare quite different from a single-phase. When a three-phase motor will not start, one or more phases are open.(See mechanical troubles for a locked rotor.) To test, youmust first check all three phases for voltage on the source

39

side (top) of the switch. Using a voltage tester, checkwith the test prods from A to B, B to C and C to A. Tocheck a three-phase switch or starter, you must have itclosed to a live circuit. Then cross-check by going fromA phase (input or top connection) to B phase (output orbottom connection). If this test shows no voltage, Bphase is open at the switch. Cross-check the other twophases in the same manner.

CAUTION: Do not attempt the above test if themotor hums but does not start. It is possible to damagethe motor while making the test. The trouble is not inthe motor if it starts when belt tension is released.

14-7. If the switch and the control circuit tests showthat they are operating correctly, the fault may be eitherin the terminal block of the motor or in one of themotor windings. Serious trouble in the motor will beindicated by evidence of overheating, such as charredinsulation or the smell of burned insulation. Suchdamage would call for the services of the electric shop,which may be able to supply you with a replacementmotor of the right horsepower and direction of rotation.

14-8. Mechanical Troubles. Mechanical troubles alsoconcern you. For example, when there is evidence that atrouble is in the compressor, here are two mechanicalcauses which are most common: (1) A locked rotor maybe caused by a frozen bearing or it can be the result ofhigh head pressure. (2) A frozen bearing occurs in thecompressor from lack of oil more often than from afaulty oil pump. Of course, a mechanical failure in thecompressor is possible, but this will seldom cause alocked rotor. The usual symptoms are an inability to coolsufficiently and noisy operation of the compressor.

14-9. Abnormal pressures. When the cause of a troubleis not obvious and the compressor will operate, gaugereadings are necessary to help spot the cause.Abnormally high head pressure indicates a restriction inthe high side. The cause may be (1) air in the system,(2) moisture in the system, (3) dirt or sludge. (4) a kinkor a pinched line, and-last but often unsuspected-(5) apartly closed valve.14-10. An abnormally low head pressure on the high

side would not be a positive indication of compressorfailure because it would also depend partly on the state ofcharge in the system and what the suction pressure gaugemeasures. Low charge is checked by looking for bubblesin the sight glass, which should show a solid flow ofliquid under normal conditions.14-11. Refrigerant controls. The refrigerant control is

the source of many troubles. Indications of a restrictionat the control are low suction pressure and an inability ofthe evaporator to pull the temperature down. Thecompressor may run continuously or it may cycle on

safety controls. Whenever the refrigerated area is toowarm, the thermostat will be calling for compressoroperation all the time. The thermostat may be checkedby turning its setting toward warmer to see that it willoperate properly. The cause of trouble at a thermostatcan be loss of charge, a pinched capillary tube, orimproper adjustment. The first two troubles wouldrequire a replacement. An ice bath and thermometer arenecessary to make the correct adjustment of athermostat.

14-12. Troubles at a refrigerant control valve arerestrictions or improper adjustment. Ice at the valve seator needle reduces the capacity of the valve and causesabnormal readings of pressure gauges. Dirt or metalparticles in the strainer can clog it to produce the sameeffect. A flare fitting which is not frostproof or one inwhich the seal has failed can cause hidden trouble. Icewill accumulate under the nut slowly, crushing the tubing.Thus, a careful inspection is necessary to reveal thedefective fitting. It is for this reason that solder jointsare preferred in below-freezing areas. Check for ice bywarming the suspected trouble spot.14-13. Adjustment of controls. Before attempting the

readjustment of an expansion valve, you should makesure that one of the following is not a cause of yourtrouble:

• A worn needle and seat.• A leaking bellows.• Ice forming on the bellows.

When a valve will not close completely, the conditionindicated might be a worn needle and seat, which can bereplaced with new parts. A leaking bellows generallyrequires that the valve be replaced. Ice forming on thebellows may be prevented by coating them with vaseline,but this will not work in zero cold areas. A bettersolution is to keep moisture out of the housing by sealingit. After a valve has been repaired, it can be tested withan expansion valve test assembly. This consists of arefrigerant tank and service valve, two gauges for high-and low-pressure readings, and a cooling chamber withcrushed ice. A source of dry air at 100-pound pressurecan be used in place of refrigerant. For low-temperaturework, dry ice may be used for the cooling chamber and alow-reading thermometer to check the temperature. Atest assembly setup is shown in figure 14. Theconnection for the gauge on the outlet side of the valveis left loose enough for escape of pressure to simulaterefrigerant low. As the valve adjustment is changed, theclosing and opening pressures are noted on the gauges. Avalve that will not adjust to its required specificationsmust be replaced.

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Figure 14. Expansion valve test assembly.

41

14-14. If replacements are made to a float valve,there is one consideration which must be observed.Operating levels of the float must be the same as theywere originally to insure proper operation. Any change inthe operating levels will change the operation of thesystem.

14-15. Condenser and Evaporator Service andRepair. Dry type condensers and evaporators are cleanedwith a stiff fiber brush or compressed air. The directionof air should be opposite to the normal flow. Thefrequency of cleaning recommended is based on a timeinterval for average conditions. The interval will beshorter when conditions require more frequent cleaning.Bent fins must be straightened to maintain adequateairflow. An outdoor mounted condenser can have a largepart of its air passages closed by hail driven against thefins by the wind. Pinhole leaks in tubing can be repairedby brazing. Use flux sparingly as excess flux may passthrough the hole into the tubing.

14-16. Pressure Testing. After extensive repairsor replacement of major components in a system, youmay be called on to check the system with high pressure.Pressure testing of a system may be done with nitrogenor carbon dioxide to determine the strength of tubingand joints. Specified test pressures as recommended byASRE in the American Code should be followed. Becareful to apply the test pressure by building up pressureslowly. Avoid sudden shock loads to the system. Takereasonable precautions to protect yourself and otherpersonnel with suitable barricades so that no one will beinjured if a line should rupture.15. Preparing To Open the System

15-1. Before you can open a system, you musttake the necessary steps to save the refrigerant in thesystem and prevent air from entering. The usualprocedure is to pump down. First, close the receiveroutlet valve and operate the compressor until the suctionpressure gauge reads 3-5 PSIG and levels off at thispressure. This indicates that pumping down is complete.At this point, the receiver inlet valve is closed and thecompressor is stopped. Of course, it may be necessary toallow some refrigerant back into the system, because thesystem should not be opened without a positive pressure.Such a procedure will keep air out and leave you lesswork to do when the time comes for you to put thesystem back into operation.

15-2. When equipment, such as a strainer, isprovided with valves and a bypass line, it is not necessaryfor you to pump down the system. One precaution isnecessary as it may be possible to trap liquid refrigerant inthe equipment when it is isolated from the system. Toavoid this, you must be careful that you do not unload adangerously high pressure accidentally, when you openthe

Figure 15. Spring caliper.

system in these circumstances. The moral? Always purgeequipment of refrigerant in the manner specified and youwill be on the safe side.

16. Open Type Compressor Overhaul16-1. Among the causes of compressor failures,

valve trouble and a lack of oil are probably the mostcommon. We will not discuss valve trouble at this time.As for a lack of oil, it can result in trouble with all of themoving parts in a compressor which require lubrication.This section deals first with the use of a micrometer tocheck dimensions and then with the special knowledgeyou should have to enable you to overhaul a compressor.Of course, the manufacturer's service book isindispensable, since it contains the overhaul instructionsfor the compressor. In it you will find those rules withwhich you should approach every job. Any exceptions tothe rules will be found in the specific instructions foreach piece of equipment. Now, let us begin by explainingspecial measuring tools.

16-2. Measuring Tools. Among the measuringtools which you must use are several types ofmicrometers and calipers. Let us consider first thosetools which are least accurate, then move on to adiscussion of the more accurate measuring tools.

16-3. Spring type caliper. Look at figure 15, whichis an illustration of spring type calipers. The accuracy ofthis type is limited to how close you can read themeasurements on a scale; it is also

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Figure 16. Caliper rule.

dependent on the amount of feel (or pressure) which youplace on the ends of the caliper when you are checking apiece of work.

16-4. Caliper rule. As shown in figure 16, thecaliper rule has one fixed jaw and one movable jawwhich slides on the rule. The sliding arm is marked withtwo lines labeled “OUT” and “IN”. For measuring anoutside diameter, the scale is read where the OUT linematches it at 51/64 inch, as shown in the bottom half ofthe illustration. To measure an inside diameter, thewidth of the jaw must be taken into account. Tomeasure the ID of a cylinder as shown in figure 16, readthe scale where the IN line matches it at 42/64 inch.The smallest ID that a caliper rule can measure is thewidth of the jaws.

16-5. Micrometers. Four types of micrometers areused in making precision measurements of machine parts.These are the outside micrometer, the inside micrometer,the depth micrometer, and the dial micrometer. Theaccuracy of these tools is no better than the skill of theuser. They must be used correctly to give precisemeasurements.

a. Outside micrometer. An outsidemicrometer is used to measure the diameter of a shaft orthe thickness of a sheet. The outside micrometer, shownin figure 17, is used to measure diameters of less than 1inch, which is the limit of movement of the barrel.Common sizes of the micrometer are 1 inch, 2 inches,and 3 inches. The rachet stop in the base of the handleis used to drive the spindle when you are taking ameasurement. The first step is to have the micrometerset wider than the shaft to be measured. Next, the shaftshould be held firmly against the anvil (fixed face) sothat the

Figure 17. Outside micrometer.

shaft is parallel with the anvil face. Use the rachet stopto drive the spindle in against the shaft. But note thatthe rachet stop is a drive which will slip. However, italways applies the same driving force to the spindle sothat results will be uniform. Figure 18 shows threeexamples of making a correct reading on a 1-inchmicrometer. Each number on the barrel marks one-tenthof an inch (0.1 inch). Between adjacent lines on thebarrel, there are twenty-five hundredths of an inch, 0.25,marked off by 25 divisions around the thimble. Eachcomplete revolution of the thimble moves the spindletwenty-five thousandths of and inch, 0.025. This is thedistance marked off between two adjacent lines on thebarrel. Four of these divisions, from the zero mark onthe barrel will bring up the number “1” on the barrel.This indicates 0.1 inch, or one-tenth of an inch. Thebottom example in figure 18 shows a micrometer set tomeasure 0.224 inch. The 0.2 is read from the barrel, andthe 0.024 is read from the thimble. In the middleexample, the correct reading is 0.226 inch, even thoughthe next line on the barrel does not show under thethimble. The position of the zero on the thimbleindicates that it has more than completed one additionalrevolution. The top example shows the barrel exposedbeyond the 0.30

Figure 18. Reading a micrometer.

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Figure 19. Reading a vernier scale.

line, indicated by the position of the thimble. The zerohas already passed the revolution line on the barrel. Amicrometer with a vernier scale can measure to tenthousandths of an inch. Figure 19 gives an enlargedpicture of the scale of a micrometer set to measure0.2862 inch. The vernier scale is etched in the barrel, thelines being parallel with its length. The vernier reading ismade by locating the line on the thimble which matchesthe vernier line on the barrel. In this case it is the 16ththimble line which matches the vernier line 2, whichgives the reading of 0.0002, or two ten-thousandths.

b. Inside micrometer. To make accuratemeas-

Figure 20. Inside micrometer with extensions.

Figure 21. Depth micrometer with extensions.

urements with an inside micrometer, you must givecareful attention to several details. Figure 20 shows theextension rods and their use with an inside micrometer.An extension rod must be absolutely clean before it ismated to the micrometer. Any particles of dirt whichprevent the extension from bottoming would causeinaccurate readings. Its length can be checked with anoutside micrometer of sufficient size. The micrometermust be held parallel with the diameter line of thecylinder being gauged. The "feel" or drag of the toolshould be only slight and is checked by holding one endfirm against the cylinder wall while the other end ismoved straight up and down. Out-of-round and runout ischecked by taking sample readings at several points of acylinder for comparison. The barrel and the thimble aremarked and read in the same manner as an outsidemicrometer.

c. Depth micrometer. The use of a depthmicrometer and its extension rods are shown in figure21. The same rules apply to the assembly of this tool asthose given for the inside micrometer. The extensionrod must be clean, and it

44

Figure 22. Dial micrometer.

must mate exactly to give accurate measurements. Youmust hold both shoulders of the gauge flush against theedge of the opening while making a measurement. Thespindle is driven by the rachet stop so that its travel willbe arrested as soon as the rod touches bottom.

d. Dial micrometer. A dial micrometer is aprecision tool in which measurements are read directly ona dial. The dial micrometer, shown in figure 22, isprovided with a handle so that it can be easily handled tocheck a cylinder wall. The steel spring at one end of themicrometer provides a two-point contact with the wall toinsure better accuracy. Runout is easily checked, as thetool gives a continuous reading while it travels down thecylinder. The dial micrometer is mounted in a fixedholder when it is used to check a shaft to see whether ornot it is true.

16-6. Compressor Disassembly. After you pumpdown a system you must frontseat the compressorsuction and discharge valves. You can then remove thecompressor from the system. However, there is one noteof caution which you should observe. Before acompressor is removed from the system, the crankcaseshould be vented and the oil drained. The drain plugshould be loosened slowly, and pressure should be bledfrom the crankcase before the plug is taken completelyout. The oil should be inspected and a note made as toits color and condition. You will find signs of wearindicated by the presence of fine particles of metal or asubstance like grit in the oil or in the bottom of thecrankcase. If the oil appears good and if there are no

signs of grit in the crankcase, you could safely assumethat the bearings were in good condition. A compressorteardown is not necessary if trouble is caused by adefective oil pump. With the oil pump system, however,there are two items which might also cause a trouble.These are the oil pressure regulating valve and the oilpressure safety switch. Failure of the regulator or switchcan cause much needless work if tests are not madeproperly. Parts which cannot be adjusted to factoryspecifications should be replaced.

16-7. What is it that we are trying to emphasizein our last paragraph? Just this! The condition of the oilis a reliable and accurate gage of internal conditions inthe compressor. Even if a mistake were made in theinterpretation of conditions, that is no reason to make amajor overhaul out of a simple replacement. Anexception to this would be where a compressor wasapproaching the end of the time interval when a majorinspection would be required. As a supervisor, you willbe expected to make wise decisions in matters of thiskind. One important item which may be overlooked isthe cause of a failure. Repairing or replacing a part is notenough unless you know the cause of a failure and takemeasures to correct it.

16-8. Oil Seals. A seal is used where thecrankshaft passes through the crankcase. This seal mustbe able to hold the pressure in the system whether theshaft is moving or at rest. One type of seal uses abellows made from a thin metal tube. One end of thetube has a flange which is secured to the crankcase, whilethe other end has a metal and graphite ring which isforced against a shoulder on the crankshaft by a spring.In this mounting, the tube is stationary. A variation onthis type has the tube and bellows mounted on the shaft,and the seal is pressed against a shoulder on thecrankcase. The main disadvantages of this type of sealare that it requires that the shoulder which the sealpresses against must be hardened and that a scratchacross the shoulder can cause the seal to leak. Newdevelopments in synthetics have led to the use ofmaterials which provide a seal without needing a speciallyhardened surface.

16-9. One new type of seal is the rotating sealhead, which is precision built and assembled at thefactory. It has a neoprene bellows, a lapped carbon sealwasher, a retainer shell, a driving band, and a flangeretainer. The seal washer mates with a stationary seat onthe cover plate. The seat is also precision lapped. Thedriving band presses the bellows against the shaft toinsure its turning with the shaft. The bellows is made sothat it will ride along the shaft, permitting end play of theshaft while maintaining contact of the seal with the seat.

45

16-10. On some compressors, a seal nut must beremoved from the shaft first before the cover plate orseal guard is removed. Check the threads carefullybefore attempting to remove the nut. A nut with a left-hand thread must be turned clockwise to loosen it.When the seal has been removed, check all of the sealfaces for scratches and signs of wear which could preventa new seal from doing its job. Remove all packingcompound and rust preventive from the new seal withapproved cleaning solvent. Failure to clean the sealthoroughly will introduce foreign grease into the system,which can cause trouble. After cleaning and drying thenew parts, mating surfaces must be coated withrefrigerant oil before assembly.

16-11. After installing a new seal, proper operationmay be checked as follows: Frontseat the suction servicevalve and run the compressor until the vacuum levels off.Then frontseat the compressor discharge valve and watchfor an increase in discharge pressure. A rise in dischargepressure indicates that air is being drawn into the system.

16-12. Valves and Plates. You will find thatsuction and discharge valves in a large compressor aremounted in a valve plate. You can replace these as acomplete assembly for each cylinder when necessary.Replacement is necessary whenever the limits specifiedby the manufacturer are exceeded. Check the depth ofthe seat for both suction and discharge valves to see thatthe amount of wear is within limits. Check the valvedisks to see that they are not worn too thin. A depthmicrometer will serve to check the depth of a seat fromthe face. An outside micrometer is used to measure thethickness of disks for evidence of wear beyondrecommended limits.

16-13. If a spring steel valve is replaced, the newvalve must seat properly. Some replacement valves willbe found with a slight burr on one side. This burr sidemust be placed up or away from the seat. Otherwise, thevalve will not seal properly, and the seat will be scored.The burr should be removed if it is heavy enough tobreak up and cause metal chips in the system. A slightfeather edge should not produce chips but does indicatethe side which should be up when it is installed. Valveseats that are of the raised type may be lapped with finecompound if the seat is worn. Care must be used thatthe lapping tool is flat. The tool must not be allowed torock during the lapping as the seal surface would be lost.All compound must be removed after the lappingoperation is completed, as a small amount of thecompound will quickly ruin every bearing in acompressor. Unless well-qualified personnel are availableto perform precision lapping, it would be advisable foryou to make valve and valve plate replacements and savework, such as lapping, for experts. Always use newgaskets with valve plates and cylinder heads. Remember

that new cylinder head gaskets must have the samethickness when installed as the old gaskets, or thecompression ratio will be changed. A gasket that is toothin will cause the compressor to be noisy, while one thatis too thick will reduce compressor efficiency.

16-14. Connecting Rods, Pistons, and Cylinders.These parts should be checked for wear against the tableof specifications for the compressor. Wear limits varyfrom as little as 0.001 inch for wrist pins and bushings toas much as 0.003 inch for cylinder sleeves. Label thecaps and rods so that they can be reinstalled in the samepositions from which they were removed. Somecompressors are provided with removable cylindersleeves. If the connecting rod will not pass through thesleeve, then the rod, piston, and sleeve must be removedtogether. You must be careful that the piston does notcome through the top of the sleeve during removal, asthe rings will give you trouble. Check bearing surfacesfor correct measurements and for scratches or other signsof damage. Lubricate pans with refrigerator oil beforereassembling them. Bearing caps should not be filedunless this action is specifically directed by themanufacturer.

16-15. Ring gap is checked by inserting the ringabout 3/8 inch from the top of the cylinder.Compression rings have a taper toward the top of thering. If installed upside down, the compressor will benoisy in operation, indicating that oil is being pumped.The top of the ring (marked "TOP") must face up so thatit will be toward the cylinder head when it is installed.Oil rings which have no taper may be installed witheither side up. Check the ring gap with a feeler gaugeafter the ring is inserted into the cylinder about 3/8 inchbelow the top. Ring gaps must be staggered around thepiston. Side clearance between the piston and ringshould be about 0.001 inch, and the ring must be free tomove. When the new rings are installed, be sure tobreak the glaze on the old cylinder wall so that the ringswill wear in properly.

16-16. Crankshaft. A crankshaft whose bearingsurfaces are worn but otherwise are in good conditionmay be used if undersize bearing inserts are available.Remember that worn bearings for the connecting rodsmay mean worn parts at other places also. So be surethat you take all factors into account before attempting arepair that may not prove satisfactory all around.

16-17. Oil Pump and Accessories. Oil pumps aregear type positive displacement to insure delivery of oil atthe pressures required for refrigeration compressors. Forexample, a system designed for oil pressure of 45 to 55p.s.i. above suction pressure should have an oil pressuregauge reading between 85 and 95 if the suction pressureis

46

40 p.s.i. An oil regulating valve of the spring-loaded typeinsures correct oil pressure automatically. Some of thesevalves are adjustable, while others are factory set. Whenpressure cannot be adjusted high enough, it may be anindication of badly worn bearings.

16-18. An oil safety switch operates on differentialpressure, which is the difference between pump dischargeand crankcase pressure. If oil pressure drops too low, thecompressor motor is shut off. Low oil pressure can resultfrom low oil, pump failure, worn bearings, and crankcasedilution by refrigerant. Diluted oil may be caused byworn rings.

16-19. After repairs are made to a compressor, thesystem may require cleaning before it can be put back inoperation. While the following section is written for ahermetic motor burnout, the cleaning procedures can beapplied to any system, large or small, which requirescleaning. The process also applies to a new system whichhas just been assembled or installed and which requirescleaning before it can be considered ready for operation.

17. System Cleaning17-1. This section is in part reprinted from April

1961, and June 1962, Refrigeration Service andContracting. A new system requires cleaning beforeoperation to insure removal of any foreign material left inthe system. Also a system requires cleaning after burnoutof a hermetic motor. In either case the method you usefor cleaning a system will be determined by prevailingconditions and by the equipment you have available.With a new system the first step is to install a filter-drierin the suction line to prevent damage to the compressor.The filter-drier is changed as often as necessary. Such achange is called for whenever suction pressure drops, asthe drop indicates a clogged filter. The followingmethods are generally considered to do a satisfactory jobof cleaning.

17-2. Cleanup Procedure for Small Capacity.After you have established that a burnout has occurred,follow the cleanup methods recommended by theequipment manufacturer. If the manufacturer's servicemanuals are not available, you may follow the proceduresoutlined in this section. The procedures that we willdiscuss in the following paragraphs apply to mosthermetic compressors. On larger systems a single filter-drier, connected in the suction line, may cause pressuredrops. If this occurs, you must use parallel driers.CAUTION: Acid burns can result from touching thesludge in a burned out compressor. You must wearrubber gloves when handling any contaminated pan.

17-3. To clean a system with a liquid line filter-drier and less than 10 pounds of refrigerant charge, youmust follow these procedures:

• Evacuate the system from the high side(discharge shutoff valve).

• Flush the system completely with newrefrigerant.

• Install the new hermetic compressor-motor.

• Install a filter-drier in the liquid line, using a sizelarger than specified.

• Charge the system with new refrigerant.• Start the system according to the manufacturer's

instructions or local SOP's.

• Check the oil and filter-drier on followup callsto establish the need for replacement.

• On the first followup call, install a moisture andliquid indicator (liquid eye) in the liquid line,after the filter-drier and before the expansionvalve. This will indicate when moisture contentis within acceptable limits.

17-4. Cleanup Procedure for Large Capacity. Theprocedure to follow if the system contains more than 10pounds of refrigerant is:

• Bleed some refrigerant from the high side. Ifthe refrigerant has a burned or acid odor, itmust be evacuated to the atmosphere. If thereis not a strong odor, you can evacuate therefrigerant into a clean, dry drum.

• If the system did not have a drier in the liquidline, you must clean the expansion valve strainerand the internal expansion valve parts.

• If the system has a drier in the liquid line,remove and discard it.

• Install the new compressor.

• Install a filter-drier in the suction line.

• Install an oversized filter-drier in the liquid line.

• Evacuate the entire system with a vacuum pumpcapable of pulling. 0.2 inches of Hg.

• Break the vacuum with refrigerant.

• Re-evacuate and charge the system with theoriginal type of refrigerant. Charging should beaccomplished through the low side of thesystem.

• Change the liquid line filter-drier and removethe filter-drier from the suction line after 48hours.

• The filter-drier in the suction line can bechanged sooner if the pressure drop affectssystem capacity, but it is considered goodpractice to leave it in the system for at least 6hours.

• Install a moisture and liquid indicator in theliquid line and check the oil color and odor. Itmust be changed if it appears dirty or smellsburned.

• In 2 weeks, recheck the oil and change it ifnecessary. The moisture indicator will showwhether or not the drier needs replacement.

17-5. Flushing the System. One of the acceptedmethods of cleaning the system after a hermetic motorburnout is flushing. Dry air, nitrogen, or

47

Figure 23. Circulator setup.

carbon dioxide gases are often used for this purpose ifthem is no sludge in the system. However, mostmanufacturers recommend the use of refrigerant (thesame as that used for system charge) the flushing agent.Purging with gases (air, nitrogen, carbon dioxide, etc.)does little good, because the sludge adheres tightly to theinternal surfaces of the system. The solvent action of therefrigerant is essential for adequate system cleanup.Refrigerant 11 has been found to be the best solvent. Itremains in liquid form at normal room temperature,because its boiling point is 74° F. at atmosphericpressure. Its cost is low, and it is readily available fromlocal wholesalers.

17-6. Circulation of the solvent (R-11) can beaccomplished with the setup shown in figure 23. Toflush the system, you would open valves B and C andclose valve A and D. Backwashing is accomplished byopening valves A and D and closing B and C. The flowof solvent through the strainer and filter-drier is always inthe same direction, as shown in figure 23. The pump isof the diaphragm type. All of these components areusually available so that you could build your owncirculator and mount it on a dolly or two-wheeled cartfor mobility.

17-7. Procedure for Cleaning a System with aCirculator. We have discussed procedures for systemcleanup. The procedure that we will discuss now isconsidered much more efficient, but to use it, a circulatoris needed. The setup for such a circulator has beenillustrated in figure 23. The procedure for cleaning asystem with a circulator follows:

• Make sure that the compressor motor is burnedout; then remove the electrical leads from themotor terminals.

• Remove the refrigerant and oil as a liquid, butdo not purge off in the gaseous state. Since, atthis time, the acid content may be high, becareful to avoid contact of it with your skin oreyes.

• Remove the filter-drier and expansion device.

• Install bypass where components were removed,except at the suction and discharge lines to thecompressor.

• Attach the circulator to the system.• Circulate the solvent for at least 4 hours.

• Change filter-drier in the circulator as frequentlyas it is necessary to insure removal of moisture.

• Shut off the circulator and blow the system outwith R-12 or R-22. Get the system as dry aspossible.

• Install the new compressor, filter-drier, andexpansion device.

• Partially charge the system and make a leak testwith a halide torch.

• Evacuate the system three times. Break vacuumwith refrigerant each time.

• Charge the system with new oil and refrigerantafter the third evacuation is complete.

• Check the system after 48 hours of operation.Change the oil if dirty, and replace the filter-drier.

• Check the system again in 40 to 60 days. Again,change the oil if necessary and replace the filter-drier.

18. Removing Moisture from the System18-1. The amount of moisture in a refrigeration

system must be kept at a minimum to providesatisfactory operation. The main sources of moisture arelow-side leaks, contaminated oil or refrigerant, andleakage in a water-cooled condensing unit. Moisture mayenter the system whenever it is open, such as duringinstallation or when you are making repairs.

18-2. Moisture Troubles. You will find that moisturein the system will cause one or more of the followingundesirable effects:

• Freezing at the expansion device.• Corrosion of metals (this forms sludge).• Copper plating.

• Chemical damage to the motor insulation or toother system components.

• A restricted or plugged filter.We will discuss two methods of dehydration, one

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Figure 24. Cutaway of a filter-drier.

using driers with desiccants and the other using vacuumpumps.

18-3. Driers. The drier unit contains desiccant,screens, and filters. Figure 24 shows the internalconstruction of a nonrefillable drier. The distributionbaffle prevents a solid stream of refrigerant from passingthrough the desiccant block. It also eliminates turbulenceand insures a smooth flow of refrigerant through thedrier. The spun glass filter is held in place by the anti-bypass ring. The ring forces a of the refrigerant to flowthrough the desiccant block and then through the porousbronze filter. The filter casing carries modelidentification and positive directional flow arrows or inletand outlet markings. The model number indicates thesize of the filter. The total charge in a system is thebasis for the size drier selected. If the total charge isunknown, you can assume that it is 8 pounds per ton forR-12 and 6 pounds per ton for R-22 and R-502. NOTE:The following general rule may be used to estimate thesystem charge in relation to the horse-power rating of thecondensing unit:

R-12 = 8 lbs/hpR-502 = 6 lbs/hpR-22 = 6 lbs/hp

The directional indication must be observed duringinstallation. If it has been connected in backwards, it willcause a restriction. Why? Because particles of desiccantwill get into the system, since the screen will be on thewrong side.

18-4. Desiccants. A desiccant is a compound capableof absorbing the moisture in the refrigerant-oil mixture.We will discuss three commonly used desiccants:activated alumina, silica gel, and calcium sulfate. Youmust be familiar with the correct use of these desiccants.All three are rated as highly acceptable, but the use of thewrong desiccant in a system can cause trouble andbreakdowns.

18-5. Activated alumina. Alumina removes moistureby absorption. It is used on systems containing sulfurdioxide (SO2), methylene chloride, methyl chloride, R-11,and R-12. It can be used in the suction or liquid line forall these refrigerants except sulfur dioxide. However, onan SO2 system, you can install it in the suction line only.Activated alumina is available in granular, ball, tablet, andsolid core form.

18-6. Silica gel. Silica gel is a glasslike silicon dioxidegel which removes moisture by absorption. It alsoremoves acids and does not dust. It is available ingranular, bead, and solid core form and is used on mostrefrigerating systems, since it is compatible with mostrefrigerants.

18-7. Calcium sulfate. The anhydrous form of calciumsulfate is also used to remove moisture from a system.Although it forms dust somewhat more than activatedalumina, it can still be left in the system permanently. Itis available in granular,

49

Figure 25. Temperature pressure relationship.

(reprinted from April 1964 RefrigerationService and Contracting).

stick, and special block form. Calcium sulfate cannot beused with SO2 refrigerant.

18-8. The reactivation temperature for these desiccantsare:

• Activated alumina 350°-600° F.

• Silica gel 350°-600° F.

• Calcium sulfate 450°-480° F.18-9. Installation of Driers. Before installation, a

drier should have both ends open and be baked in anoven at 300° F. for 24 hours. The drier should becapped after baking to prevent accumulation of moisture.Caps are removed just before the drier is placed in thesystem. Even a drier which has been sealed by themanufacturer should be dried before installation if thereis any reason to suspect that moisture may have passedthe seals.

18-10. Dehydrating with a Vacuum Pump. Thismaterial is in part reprinted from April 1964 RefrigerationService and Contracting. To start our discussion, let us

think of pressure as the column of mercury it willsupport. Think of atmospheric pressure as equal to 29.92inches of mercury instead of 14.7 p.s.i.g. at sea level.This will permit us to use the pressure-temperaturerelationship shown in figure 25 when we determine thevacuum which must be attained to boil water at variousambient temperatures.

18-11. Referring to figure 25, a vacuum pumpcapable of eliminating all but 1 inch of Hg is able toremove moisture at an ambient temperature of 80° F. ormore. While a pump pulling within 1 inch of Hg, caneliminate moisture, it must also be capable of holding thisvacuum throughout the dehydration process. Before weconsider the variables that affect a vacuum pump'sperformance, we should first review some generalclassifications of pumps relative to their ability to removemoisture by the boding process.

18-12. The piston type compressor might pull avacuum of 28.2 inches of Hg, which is actually 1.7 inchesof Hg on a manometer. Quite a number of these pumpshave been used for vacuum work, but they areimpractical in removing water by the boiling method.Under normal ambient temperature, moisturecontaminates the crankcase oil.

18-13. A rotary type compressor can pull a vacuumof 29.63 inches of Hg,. This pressure will cause the waterto boil at an ambient temperature of approximately 45° F.For these reasons, the rotary compressor is practical foruse as a vacuum pump.

18-14. The compound two-stage high vacuumpump is capable of pulling down to about 50 microns forprolonged periods of time. Because such pumps are two-stage pumps, they can be equipped with a gas ballast orvented exhaust. The gas ballast or vented exhaustfeature is a valving arrangement which permits relativelydry air from the atmosphere to enter the second stage ofthe pump. This air mixes with the air being passed fromthe first to second stage and helps to prevent themoisture from condensing into a liquid and mixing withthe vacuum-pump oil.

18-15. Frequent vacuum-pump oil changes shouldbe anticipated and recognized as the single mostimportant factor in preventive maintenance. Even apump equipped with a vented exhaust cannot handlelarge amounts of moisture without having some of itcondense into the oil. If the water is allowed to remainin the pump, the moisture will attack the metal pans andresult in a loss of efficiency or capacity. The oil shouldbe changed after each major evacuation or dehydrationprocess.

18-16. When, you are determining the size of thepump (c.f.m. capacity) to meet your needs, you mustremember that the length and diameter of the line beingdehydrated dictates the size pump to be used. The 75-c.f.m. capacity pump will handle most applications, sincethe system is normally dehydrated through a 1/4-inchline.

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Review Exercises

The following exercises are study aids. Write your answersin pencil in the space provided after each exercise. Use theblank pages to record other notes on the chapter content.Immediately check your answers with the key at the end of thetest. Do not submit your answers for grading.

1. Why would a bottle type water cooler have afreezestat in the control circuit when thethermostat is t so that ice will form? (8-2)

2. What is the purpose of a precooler in a bubblerfountain? (8-3)

3. Of several methods you may use when patchinga leak in a water tank or line, in which methodmust precautions be observed for good health?(8-5)

4. Describe the adjustment you would make to abeverage cabinet used to cool four differentkinds of bottled beverages. (9-2)

5. When checking a condenser for warm spots,how might a warm coil be misleading to you?(9-3)

6. What is the big difference that distinguishestypes of ice making machines? Give someexamples. (10-1)

7. What are three types of evaporators you mayfind in an ice cube machine? (10-4-6)

8. Why is frequent blowdown necessary in icemaking machine? (10-8)

9. In addition to mechanical troubles, what is thebiggest source of trouble with ice makingmachines? (10-12)

10. Why is a heat exchanger necessary in the liquidline of the soda fountain shown figure 11? (11-1)

11. A dry type coil like the beverage cooler in figure11 must be correctly sized for what reason? (11-2)

12. What is the function of the water pump in asoda fountain carbonator? (11-3)

13. If you find the water pump for a carbonator isrunning continuously, where would you checkfirst to try to locate the trouble? (11-4)

14. What simple test can be made to prove that abreak in the ground circuit has caused thecarbonator pump motor to run continuously?(11-4)

15. What might cause constant complaints of havingbad taste or flavor from a storage cabinet whichhas been properly refrigerated? (12-2)

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16. On older models not provided with automaticdefrosting. what must be done before water isused for evaporator defrosting? (12-3)

17. What is meant by a “double duty” displaycabinet (12-5)

18. In addition to special illumination, what otherfeature may be found around the door of adisplay cabinet? (12-6)

19. Why must there be a continuous flow of cold airin the display section of a refrigerated opendisplay case? (12-7)

20. Give the five methods you have studied forstorage cabinet defrosting. (12-8)

21. What is the limitation on compressor off-timedefrosting? (12-9)

22. Describe the reverse cycle used for cabinetdefrosting. (12-11)

23. What is one purpose of using a high-temperaturecontrol in a low-temperature cabinet? (12-15)

24. What is the purpose of the capillary tubeconnected to a defrost valve? (12-16)

25. The service valves in a system serve whatpurpose? (13-4)

26. Give the advantage or characteristic of twotypes of water-cooled condensers. (13-7)

27. Why must a receiver be sized to the system?(13-8)

28. What is peculiar about a receiver outlet valve?(13-8)

29. How might reversed flow affect a drier-strainer?(13-9)

30. What are the three features considered essentialin an expansion valve? (13-11)

31. Give the reasons why a water cooler can use anautomatic constant pressure expansion valve.(13-12)

32. What is the purpose of an equalizer line with anexpansion valve? (13-12)

33. Give the descriptive items you would use toidentify a thermostatic expansion valve. (13-13)

34. What are the three kinds of charge used in thebulb and capillary of a thermostatic expansionvalve? (13-13)

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35. Explain the meaning of a cross charge. (13-13)

36. Give the arguments for and against the liquidcharged bulb. (13-13)

37. Give the pros and cons for a gas-charged bulb.(13-13)

38. What are the advantages of a high-side floatvalve? (13-14)

39. What effect is produced by a layer of oil on topof the refrigerant? (13-15)

40. Before making tests on a "live" circuit, whyshould you remove rings ad not wear a metalwatchband? (14-2)

41. When you find a circuit breaker tripped, whatelse should you do besides resetting the breaker?(14-4)

42. A compressor motor will not start and anammeter test reads full LRA. For what purposewould you release belt tension? (14-5, 6; also 5-11)

43. Why is it poor practice to try repeatedly to starta motor which does not turn over? (14-6, 8)

44. List the causes of abnormally high headpressure. (14-9)

45. You find a compressor unit continuouslyrunning yet unable to cool sufficiently. Whatchecks would you make to locate the cause ofthe trouble? (14-10, 11)

46. How would a compressor act if the thermostatcontrolling it had lost the charge from itscapillary? (14-11)

47. How would you make a quick check for iceblocking a refrigerant control? (14-12)

48. What is the indication of a worn needle and seatin an expansion valve? (14-13)

49. When adjustments or repairs are being made toa float valve, what consideration must youobserve? (14-14)

50. Where a drier-strainer is provided with valvesand a refrigerant bypass, what precautions mustyou observe before you remove the item fromthe system? (15-2)

51. What is the purpose of a rachet stop in anoutside micrometer? (16-5)

52. In figure 18, the top illustration shows an arrowat the right on the thimble. If the thimble isturned 12 divisions in the direction of the arrow,what will be the reading of the micrometer? (16-15)

53. How can you check to see that an extension rodwith an inside micrometer is properly seated togive correct readings? (16-5)

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54. What is the best tool to use to check acrankshaft to see whether or not it is true? (16-5)

55. Give five causes for loss of oil pressure in acompressor. (16-6, 18)

56. When installing a new oil seal, what precautionsshould you observe? (16-8-10)

57. How is a compressor operated to check a newseal for a leak? (16-11)

58. What are two important checks which youshould make when you are inspectingcompressor valves? (16-12)

59. Replacement valves made of spring steel shouldbe inspected before installation. How shouldyou perform this inspection? (16-13)

60. What is the difference between most oil ringsand compression rings used in a refrigerationcompressor? (16-15)

61. How would you obtain indications that a set ofcompression rings has been installed upsidedown? (16-15)

62. How would you check the ring gap of the ringsused in a refrigeration compressor? (16-15)

63. Unless cylinder sleeves are replaced, what mustalso be done when a new set of rings isinstalled? (16-15)

64. What other factors must be taken into accountwhen bearing inserts are replaced? (16-16)

65. When is system cleaning required? (16-19)

66. After a hermetic motor burnout, why must youuse precautions when cleaning the system? (17-2,7)

67. In system cleaning, where is evacuationequipment connected and why? (17-3)

68. Why is a new filter-drier installed after a systemis cleaned? (17-3)

69. What is the purpose of using refrigerant to breakthe vacuum when cleaning a system? (17-4, 7)

70. What is the limitation on the use of activatedalumina drier? (18-5)

71. Which system is not compatible with anhydrouscalcium sulfate as a drier? (18-7)

72. What are the general procedures recommendedbefore a drier is installed? (18-9)

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73. What vacuum is necessary to boil water at aroom temperature of 80° F.? (18-11)

74. Why are frequent oil changes recommended forthe oil in a vacuum pump? (18-15)

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CHAPTER 3

Cold Storage and Ice Plants

DO YOU SUPPOSE that this chapter should beintroduced with the importance of preserving food?Perhaps. But for a change, let us consider your job if youare assigned to work at a cold storage warehouse or anice plant. You can make the job dull and boring or veryinteresting. In the operation of a plant there will usuallybe some time each day when you will have nothing to dobut observe the equipment. The wise man will use thistime to study the equipment. He will learn how it is laidout and where the various parts are located. While youare taking readings, you should make a mental note ofchanges which you observe and try to determine thecauses of the changes. In this way you will both pass thetime quickly and become more familiar with yourequipment's proper operation. Remember, too, the manwho is alert to operating conditions will recognize thesymptoms of impending trouble and can thus oftenprevent a major breakdown. The larger plants areattended by operators on shift duty 24 hours a day.

2. This chapter is divided into two major headings.The first covers the design, insulation, layout, andoperation and maintenance of large cold storage plants.The second covers the layout, operating principles,components, and the ammonia system operation andmaintenance. We will undertake the discussion of a largecold storage plant first.

19. Large Cold Storage Plants19-1. Have you ever observed the different types of

cold storage in a commissary store? You will find similarareas in a large cold storage plant. Let us consider theeffect of these areas on the design of a plant.

19-2. Plant Design. In the layout of a refrigeratedwarehouse, consideration is given to the operatingtemperatures by using the center of the building for thecoldest operations. Warmer rooms are located aroundthe center and act as a buffer for the colder areas. Thetemperatures of the rooms which follow are presented asexamples of one warehouse.

19-3. Rail rooms. A refrigerated warehouse is usuallylaid out in the shape of a rectangle. The two longestsides of the building are occupied by rail rooms. Meathooks suspended from an over head rail provide themeans for moving heavy loads. The rail room isnormally maintained at about 35° F. Inside doors provideaccess to the processing room and meat cooler room,which are also part of the overhead rail system.

19-4. Processing room. This room is held at 45° F.,and because of its warmer temperature, it is located atone end of the building. This is where the butcher cuts acarcass into smaller parts before storage or distribution.Such processing rooms are dangerous areas. Duringnormal operations the floors become extremely slippery;therefore, you must be careful in order not to fallwhenever your work requires that you pass through theserooms.

19-5. Meat cooler. A temperature of 30° F. should bemaintained in the meat cooler for holding fresh meatprior to distribution. A meat holding and issue room at30° F. provides additional storage area for the samepurpose.

19-6. Milk, butter, and egg room. This area is normallyheld at 35° F. and is one of the colder areas.

19-7. Fruit and vegetable room. An average temperatureof 40° F. is recommended for general storage, so thisroom is also eligible for location by an outside wall.

19-8. Potato room. You may already know thatpotatoes in storage give off heat and carbon dioxide.Consequently, the potato room should have a high ceilingand must have positive ventilation to insure the safety ofpersonnel. Otherwise, the carbon dioxide will form adense layer at the floor if the fans are turned off. Anunsuspecting person would not realize his danger in anatmosphere so heavy with carbon dioxide until he felthimself fainting. Then it would be too late for him, asasphyxiation follows quickly. Furthermore, potatoesshould not be piled more than 6 feet high to insureremoval of heat. If the pile is too high, the heat will notbe removed fast enough, and they

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will spoil rapidly. Outside air ducts are used to bringfresh air into the room by means of fans. The fresh airis directed across the evaporator coils for cooling. Toinsure the safety of personnel, operating instructions forthis room must be strictly observed. Operatingtemperatures from 35° to 45° F. may be used, dependingon the type of potatoes in storage. Early crop potatoeskeep best 50° F. but must be considered for short-termstorage of less than 3 months. Late-crop potatoes willage best and keep from 5 to 8 months if the storageroom is kept between 35° and 40°. In very cold weather,heaters are turned on to keep the products from beingfrozen.

19-9. Freezer room. Occupying the center of thewarehouse are the freezer rooms. A below-zero room isused both for freeing products and for long-term storage.Products already frozen may be kept in a 10° F. room,where storage is for a short period, such as a week. Ifthe insulation is installed properly in the cold rooms, yourjob will be easier, because the refrigeration equipmentwill not be overloaded. The total heat load of thewarehouse will be lighter than if the rooms were poorlyinsulated.19-10. Vapor Barriers and Insulation. Information on

insulation is in part reprinted from January 1964Refrigeration Service and Contracting. There was a timewhen a cold storage warehouse was insulated withsawdust. But now, new materials and methods ofinstallation produce improved construction. You must befamiliar with these improvements so that you canproperly maintain equipment in rooms with moderninsulation. There are four basic fundamentals to beconsidered in construction of a modern cold storageroom. These are:

• Design the structure so the room and thebuilding can move independently of each other.

• Apply a continuous vapor barrier on the warmside of the insulation, using a plastic film orlaminate with the lowest permeability.

• Select insulation which has a permeability ratingconsiderably higher than the vapor barrier buthas a low permeability to air.

• Select a finish with a permeability ratingconsiderably highest than the insulation.

19-11. The vapor barrier should consist of a plastic filmor laminate with the lowest "permeability value" available.The value in permeability equals the number of grains ofmoisture that will pass through 1 square foot of thematerial in 1 hour under a vapor pressure differential of 1inch of mercury. It has been found that a building usingplastic film as a vapor barrier is more efficient thermallyand less costly as compared with a building using the

common adhesive or hot asphalt treated insulation. Astructure constructed according to the four fundamentalswill allow the insulated room to move independently ofthe building structure. This means that when propertechniques are followed for the installation of the vaporbarrier, the vapor seal at the wall-ceiling juncture remainsintact, and no leakage occurs at the joint. Modemconstruction allows the outer shell of the building tobreathe with changes in ambient temperature while thecold storage room is held stationary in a narrowtemperature range. If the original vapor barrier adhesivewas inadequate or ruptured, a moisture vapor and air leakwould occur and cause deterioration of the insulation.19-12. With a new construction which follows the four

basic fundamentals, the vapor barrier is installed prior tothe insulation. This vapor barrier is not cemented to thewalls of the building structure or the insulation but issupported independently of them. This is very important,since it allows building and cold room movement to haveno effect upon the integrity of the vapor barrier. Ineffect, the insulation is enveloped in a vapor barrier onthe warm side. This vapor barrier can be inspected afterinstallation prior to the application of the insulation. Donot overlook the importance of being able to inspect thevapor barrier to insure adequate protection from vaporand airflow. Any damage can be repaired a this time,and overlaps can be carefully inspected to se whetherspecifications have been followed.19-13. Insulating materials. Materials which have been

used successfully include 6 to 8 mil polyethylene film inwide sheets, laminates of aluminum foil with polyesterfilm, and creped paper. The width is sufficient to greatlyreduce the number of laps and joints. Laps and jointsrequire sealing with vapor barrier pressure sensitive tape.Some contractors use rolls of foil laminates because of itscase of application. The insulation is installed drywithout adhesives. A vapor permeable finish is applied tohold it in place. The finish protects it from damage andprovides a sanitary washable surface. In some cases thefinish is fire resistant. With proper materials, any smallamount of vapor which does pass through the vaporbarrier can flow through the insulation without changingits state. It remains as a vapor to be condensed on thecooling coil. The moisture does no condense within theinsulation to impair its thermal efficiency, and the coolingload due to heat gain trough the insulation remainsrelatively constant at or near its original U-factor.19-14. Sealing fasteners. The fastener locations on the

framing should be premarked and a strip of caulkingribbon placed behind each location. This will seal thehole in the vapor barrier caused by the fastener. Afterthe framing for the ceiling is installed, the vapor barriersheet is spot

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stapled to the inside of the framing. Seal the ceilingvapor barrier to the wall barriers with vapor barrierpressure-sensitive tape. The ceiling framing is securelyfastened to the top of all wall framing members so thatmovement of the building will not affect the wall-ceilingjuncture. The framing for the self-supporting wallsshould also rest on a plate securely fastened through thefloor vapor barrier into the subslab.19-15. After the necessary bracing is in place, the vapor

barrier is installed on the self-supporting walls. It isinstalled on the outer side of the framing and sealed tothe overlap of the ceiling vapor barrier. The first layer ofinsulation is force-fitted between the wall studs andnailed to the underside of the ceiling. The second layeris installed horizontally on the walls and perpendicular tothe ceiling framing under the suspended ceiling. Thislayer is held in place with plastic skewers or nails.19-16. Lay polyethylene vapor barrier over the subslab

and tape all joints and seal with tape to the ends of thewall vapor barrier. You will then be ready to lay in theinsulation. The joints must be tight. Then lay a vaporpermeable sheet, such as 15-pound roofing felt, over thefloor insulation and up over the wall insulation, above theheight of the concrete curb that will be poured later.Also pour the concrete wearing slab and install a curb ofthe proper height. After this, cut off the 15-pound felteven with the top of the curb. The felts acts as a slipsheet. It allows the floor and curb to moveindependently of the walls. It also prevents excess waterin the concrete from wetting the floor insulation.19-17. At this point, the job is ready for installation of

the permanent fasteners and the stabilizers. Fasten 4-inch-wide galvanized metal lath over each framingmember. Apply a portland cement finish in two coatsover the walls and ceilings. The finish should be curedwith water spraying in accordance with recommendationsfor wiring. This treatment reduces shrinkage and givesmaximum strength to the finish.19-18. Plant Layout. In order to understand the layout

of a cold storage plant, you should be able to readblueprints. Standard drawings are often used withadditions and note added so that the diagram may beapplied to a specific installation. You should recognizethat this is the case with the illustrations used in thissection. At the time when a facility is built, an accuratedrawing is made of the equipment. These drawings arereferred to as "as-built drawings." Changes ormodification should be entered in the drawings; thus thedrawings should be kept up to date by appropriate entriesof modifications or additions to the plant.19-19. Machine room. If you have ever seen the

machine room in a cold storage plant, you were probably

impressed by the array of tubing. Some of it yourecognized without a doubt, while other parts of thetubing seemed strange to you. Look at figure 26 and youwill see a diagram of the layout of tubing and equipmentin a machine room. Appropriate labels are provided sothat you can identify each item. Notice how a pitch isspecified for horizontal lines to prevent pockets of liquidfrom being trapped in the lines. A few words ofexplanation may help you to read such a diagram.19-20. Look at the upper right part of figure 26 and

find a line which is labeled "LL to HT System coolers."The abbreviation means liquid line to high-temperature-system coolers. At the upper left you will find a linemarked "S.L. 4," which means "4-inch suction line."Beside the legend "Sight glasses" you will see a number"1" in a small triangle. This 1 refers to an item whichwas added after construction has been completed. Whenitems are added, such as symbols with special meaning., anotation should be made under "added notes" or"revisions" on the blueprint. Appropriate forms, such asstatus and operational records, component replacement,and historical records, must be maintained for plantequipment as directed by inspection TO's.19-21. Under the label "Liquid Receiver" is a note

telling you to "See detail." Several details may be shownon the same blueprint. A detail of a typical receiver isshown in figure 27. Note the two driers, which makes itpossible to replace one without shutting down the system.You can see many things in the detail which could not beincluded in figure 26 because of lack of space.19-22. Cold rooms and evaporators. The various cold

rooms are provided with evaporators of appropriate size.In figure 28 you will find a detail of typical connectionsto an evaporator. Each large cold room may have one ormore evaporators, and valves must be located so that anevaporator can be isolated while the rest of systemremains operating. Let us now consider the operationand maintenance of a cold storage plant.19-23. Operation and Maintenance. For purposes of

this discussion, we will start with the motor controls andcompressors and follow the flow of refrigerant. Thus, wecan explain the operation of the plant in a logicalsequence.19-24. Compressors, controls, and accessories. From our

previous discussion of a machine room, you willremember the four compressors shown in figure 26.Two 15-hp compressors supplied the high-temperatureevaporators, while two 20-hp units furnished the low-temperature evaporators. In either side, the loss of onecompressor will not halt operations completely. Whenpossible, compressors of the same size are installed sothat the

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Figure 26. Machine room diagram.

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Figure 27. Detail of liquid receiver.

system can be standardized and spare parts will beinterchangeable. The inventory of spare parts will thusbe smaller because there will not be a need forduplication.

a. Pressure control. Generally, motors larger than5 hp are three phase and require a starter. The motorstarter is controlled with a pressure motor control tappedinto the low-side suction line. The cutout pressure is setfor 10° F. below the coil temperature, while the cut-inpressure should be set for the desired coil temperature.The spread between the two settings determines thefrequency of compressor operation. Operation in verycold weather may produce conditions which will preventsome systems from operating automatically because ofabnormal pressure. The receiver outlet valve (king valve)may be throttled so as to force the pressure to increase.As pressure builds up to a near normal level, the valveshould be opened more. Be sure, however, to restorevalves to normal operating positions after the condition is

corrected. Remember, a pressure control's function is toclose and open a set of contacts in the circuit to theoperating coil of the starter for the motor.

b. Magnetic starter. The motor control isessentially a three-phase magnetic switch which is closedwhen its coil is energized. The coil serves to close theswitch and to hold it closed. The switch is closed againstspring pressure, which throws the contacts open as soonas the circuit to the coil is interrupted. Two overloadprotection provide protection against shorts in all threephases. Protectors are located in A and C phases, whichshould be the two outside wires. Remember, whentesting a switch for supply voltage, the upper terminalsare connected to the feeders. Check the upper terminalsfrom A to B, B to C, and A to C for voltage on all threephases. If one phase is dead, the trouble is in the feederor supply. The lower three terminals are connected tothe motor. When a small fourth contact is part of aswitch,

Figure 28. Detail of evaporator connections.

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it provides a holding circuit to the closing coil. Thewiring diagram inside the cover of the switch box willgive the wiring diagram for that particular switch.Maintenance consists in replacement of overloadprotectors which have failed or a magnetic coil which hasan open circuit. In both cases an exact replacement or asubstitute as specified by the manufacturer must be used.If the switch contacts are severely burned, the entireswitch may require replacement. Excessive heat maydamage other parts, such as the springs, which wouldcause more trouble in the future if the switch was partlyrebuilt.

c. Time-delay relay. You will remember that inthe illustration of a machine room, each system wassupplied by two compressors. If both these motors werestarted at the same time, there would be twice the loadon the electrical system. For example, a three-phase,220-volt, 15-hp motor will draw about 100 amperesstarting current. If both motors started together, thecombined load of 200 amperes would cause a voltagedrop, resulting in slower starting. This would extend thestarting period, and the motor windings would besubjected to unnecessary overheating. Such a situation isavoided by using a time-delay relay with one motor sothat it is not started until the other motor reachesoperating speed. A time interval of from 3 to 8 secondsis sufficient. The time-delay relay consist of a solenoidcoil and plunger with a set of contacts which close thecircuit to one of the motor starters. The plunger operatesin a dashpot filled with oil. Maintenance requires thatthe relay be kept clean. If oil needs replacing, be sure touse oil that is approved for use in a dashpot. Dash-potoil keeps the same viscosity over a wide range oftemperature. The time interval can be changed byturning the adjustment screw. An ordinary light switchmaybe wired in parallel with the time-delay relay if therelay fails. The second compressor can then be startedmanually after the first compressor starts. Operation canthus be continued until the relay can be replaced.

d. Motors and drives. Three-phase motors havethe high starting toque required by large compressors.Once a motor is installed properly, all it needs is cleaningand oiling. Motor bearings should be checked daily fornormal temperatures. They should not be so hot thatyou cannot hold your hand comfortably on the bearingshell. Always open the motor switch before checking thebelt driver end. Lubrication of motor bearings it done ona regular schedule as directed. Proper installation meansthat the motor must be lined up so that its pulley drum isparallel with, and in the same plane as, the pulley on thecompressor shaft. An initial test of the direction ofrotation of the motor should be made before theterminal’s connections are made permanent and insulated

with tape. If at the test, the motor rotates incorrectly, itsdirection is reversed by interchanging two of the motorleads with the supply leads. By transposing two of thephases, a three-phase motor will have its rotationreversed.

You may have to remove a motor at some time forrepairs. Before disconnecting the wires, be sure that youattach labels to all of the supply leads and the motorleads. Then, when you are ready to reconnect the motor,wire it the same as before.

A large compressor is driven by multiple V-belts,which should be provided with a safety enclosure. Beltguards are for your protection and must always be inplace during normal operation. Loose or damaged guardsmust be repaired or replaced. Always open thecompressor switch so that the motor cannot start whileyou are working around or in the immediate area of thebelts. If the oil is spilled on V-belts, they must becleaned immediately. Again, open the compressor switchso that the unit cannot start while you are working on it.If the oil soaks into the belts before they can be cleaned,plan on replacing the set soon, because oil causes thematerial to deteriorate rapidly.

Multiple drives of four or five belts are common.When one belt becomes too loose or worn, it may beremoved and operation continued temporarily. Youshould expect some drop in output from the compressorbecause of belt slippage. It is impractical to replace onebelt at a time, because V-belts are supplied in matchedset. However, you will always find some variation inindividual length. This variation becomes apparent whenyou try to adjust the tension on a newly installed set.When you need to replace a set of belts, be sure tofollow all relevant safety rules. First, open the electricalsupply switch to the motor. Then hang a caution ordanger tag on the switch handle if there is any possibilitythat someone might close the switch while you wereworking on the motor. Next, release the holding boltsand the locknut on the jackscrew. Also, back off thejackscrew to release tension on the belts, remove the oldset and install a matched set of belts on the pulleys.After this, take up the jackscrew until belt deflectionindicates correct tension; then, set the locknut on thejackscrew and tighten the holding bolts.

You will find some variation in belt tensionrecommendations, but these are determined by operatingconditions. For instance one beltmaker recommends abelt deflection of from 1/2 to ¾ inch for each footbetween the pulley shafts. In contrast, anotherrecommendation calls for a deflection of 1/64 inch perinch of span between pulley shafts. Experience isprobably your best gauge as to the correct tension. Inoperation, too little

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tension is indicated when most of the belts show apronounced flutter. As an example, the right tension ona matched set of belts may be most nearly correct whenone belt shows a small flutter while the rest are steadyduring operation. The object of adjustment is to get aminimum amount of vibration without getting the beltstoo tight. Belts which are too tight will wear out quickly.On the other hand, belts which are too loose will slip andresult in lost efficiency and reduced output. In any case,most V-belts are made of material which will not glaze.Belt dressing should never be used on V-belts unless it isrecommended by the manufacturer. When adjustmentwill not correct belt slippage, it would at best be atemporary measure to apply a dressing, and you shouldplan to replace the set.

e. Gauges and records. The gauge for highpressure and low pressure are located on a single panel sothat the operating conditions can be observed quickly.Alarms and indicator lights are also mounted on thesame panel. Oil pressure gauges may be on the panel butare generally mounted on the compressor. Readings aretaken at regular intervals to check for normal operation.You, as a supervisor, may require readings madecontinuously to monitor the system during unusualconditions, such as when the system is first placed inoperation after major repairs. The period of closeobservation may be long or short, depending on whatchanges have been made ad how long it will take thesystem to settle down into a normal pattern of operation.

Abnormal pressure changes are indications whichmust be interpreted correctly. A gradual change inpressure may be from a change in ambient temperature,from loading or unloading work in the cold rooms, orfrom a trouble developing. A rapid change in pressure isusually an indication of trouble. The possibility of thislatter, rapid change points up the advantage of makingfrequent readings and recording them. If the gaugeshave not been checked in several hours and a big changehas been noted in pressure, the operator may have noway of knowing whether the change is sudden or gradual.For example, when the ambient temperature drops lowduring a cold winter's night, you an expect below-normalgauge readings.If you are fortunate enough to pull an assignment at aplant equipped with automatic temperature and pressurerecorders, you will be able to read a continuous record ofplant operation. An automatic recorder has one or morepens which trace a line in ink on appropriately markedgraph paper. The pens are delicately balanced and drivenelectrically by a bridge circuit. Be careful, however, whenchanging charts or putting ink in the pen reservoir, sincerough treatment will damage the pen’s mounting and

cause an error in the recording. You may still berequired to make one or more readings of the gaugeseach shift. Your records serve as a double check onsystem operation. The best part about a graph chart isthat the frequency and duration of each cycle ofoperation can be seen clearly at a glance. The chart is auseful tool for the supervisor because, by comparingcharts, he can detect day-to-day changes.

f. Oil receivers. The oil receivers provide a meansof temporary storage of the oil returned from the oilseparators. Sight glasses provide a means of checking theoil level in the receiver. Oscillation of the oil levelindicates that the oil separators are performing theirfunction of returning oil to the receiver. The oil levelwill drop each time that the float valve opens to returnoil to the compressors. In case of low oil level, do notadd oil to the system until you have determined that oilhas been lost. Why? Because the low level can be anindication that oil is accumulating in one of evaporators.19-25. Condensers and water towers. Two types of

condensers are favored for large systems. These are theevaporative and the tube-and-shell types of condensers.

a. Evaporative condenser. You will find the firsttype illustrated in figure 29. The upper section of theunit contains the blowers, which pull air through thecoils. The center section contains an array of sprayheaders, which spray water over the condenser coils. Thecombination of air and water acts to produce a watertemperature considerably lower than the air because ofevaporation. Efficiency of the condenser falls off ashumidity goes up. The water pump circulates water fromthe sump up to the spray headers. Makeup water isadded to the sump by means of a valve and float controllocated in the sump near the pump intake. Bleed-offwater is tapped from the far side of the sump addischarged to the sewer. Bleed-off and makeupconnections are not shown in figure 29. Bleed-off watermust drain at a rate sufficient to insure that salts do notaccumulate in the unit. The condenser operation wouldbe seriously lowered by even a small salt deposit. If saltsstart to appear, it is advisable to increase the amount ofmakeup water by opening the bleed-off valve wider.When scale appears on the condenser coils, they must becleaned with a stiff bristle brush. Bristles must be hardenough to remove the scale but not so hard as to damagethe tubing. Water which has an acid pH will not causescale, but too much acid will cause corrosion.

Operation in cold weather may require the pump to beturned off. In extreme cold the fans may have to bestopped and the water drained to prevent freezing.

Capacity control of a condenser is necessary to

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Figure 29. Layout of an evaporative condenser.

insure efficiency of the system. There are four ways tocontrol the capacity of the condenser. One methodcontrols the water pump by a pressure-operated switch.When head pressure drops below a predetermined point,the pump is stopped and the unit acts as an air-cooledcondenser. Another method is to use a pressure-operatedswitch to turn off the blowers when pressure drops to apredetermined point. Still another method is to use atwo-coil condenser, with a solenoid valve to cut one coiloff when a pressure switch operates at its low-pressuresetting. A fourth method uses modulating dampers onthe air inlet. The dampers are designed to close whenthe compressor is idle. This last method has advantagesfor cold weather operation as the dampers may beoperated so that freezing of the water is not a problem.

b. Tube-and-shell condenser. Another type ofcondenser is the tube-and-shell, which circulates waterthrough the tube. The condenser shell may also serve asa receiver for the system. The condenser water iscirculated through a cooling tower, where evaporationdrops the temperature of the water. The spray headers ina cooling tower are similar to those shown in figure 29.A water bypass line around the tower is the usual methodof capacity control. This also serves for cold weatheroperation, but in extreme cold the system may have to bedrained to prevent freezing and breaking of pipes.Makeup water is added to the system automatically bymeans of a float control in the sump. Bleed-off watermay be used as a method of scale control. Algae controland water treatment are discussed in Volume 4. Capacitycontrol may also be attained by means of a water-

regulating valve located n the condenser inlet water pipe.The valve is controlled by compressor discharge pressureso that head pressure remains relatively constant within apredetermined range. The water regulating valve is amodulating type which controls the volume of waterthrough the condenser. Where water is cheap andplentiful, it may be discharged overboard after passingthrough the condenser instead of recirculating it througha cooling tower. Both evaporative condensers andcooling towers accumulate sludge which must be flushed.The unit must be taken out of service, the sump drained,and the mud removed. Twice a year cleaning should besufficient, except where dust conditions are very severe.19-26. Liquid refrigerant receivers. The liquid receiver

must be large enough to hold all of the refrigerant in thesystem. Any time the system is to be opened, it mustfirst be pumped down. This is done by closing thereceiver discharge (king) valve and operating thecompressor until the suction pressure levels off at 3-5PSIG indicating that the system has been pumped down.The receiver inlet valve is then closed, and all therefrigerant is stored in the receiver. Repairing of leaks,testing and major repairs has been explained in thepreceding chapter.19-27. Expansion valves. Expansion valves should be

checked during each walk-through inspection. Look forunusual signs of frosting or extension of the frost line onthe tubing. Frost on the high side of the valve indicatesa restriction in the liquid line. Check fans for operation.Note also any unusual noises, such as hissing, whichwould indicate a low refrigerant change. When a

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expansion valve begins to get plugged, a from ice whichis formed by moisture in the system, one of theobservable signs will be an unaccountable rise in thetemperature of the room. When this happens, you mustdo more than just clean out the valve. In addition, thesystem drier should be changed and the system carefullychecked to find where the moisture is getting in. Theleak must be on the suction side at a joint, unless thetubing has been punctured.19-28. Evaporators. The evaporator used in a cold

room is a coil and fin type with a fan or blower forcooling. Hot gas defrosting is the most practical methodfor zero operation, but some older units may still requiremanual defrosting with water. These methods are thesame as those you studied in the last chapter.19-29. Evaporators and blowers should be inspected for

security of their mountings. Any unusual noises shouldbe investigated and traced to their source. Unusual odorsin a cold room may be caused by a hot motor or abearing which needs lubrication. Conditions which youcannot correct should be reported so that proper actioncan be taken.19-30. A large evaporator in a zero cold room may

become sluggish in operation over a period of time.These conditions are caused by a gradual accumulation ofoil in the coils. A hot gas defrost system will usuallyprevent the oil from condensing in the evaporator.However, this discussion of oil condensing in theevaporator brings up one of the big advantages ofdefrosting with hot gas. Should oil accumulate in one ofthe evaporators, the first indication would be a drop in oillevel at the oil receiver with no external signs of the loss.By operating the hot gas system for an additional periodof time, the oil can be picked up by the refrigerant gasand moved out of the evaporator. The success of thisoperation will be reflected by a rise in the level at the oilreceiver.

20. Ice Plants20-1. Both portable and permanent type of ice plants

are used by the military. You may find the portable plantin sizes ranging from 1-ton to 15-ton units using standardhalocarbon refrigerants. The operation of a system usingsuch a refrigerant has already been explained. While thissection will deal with a permanent type plant using anammonia system, ice making is done by the sameprocedure regardless of which refrigerant is used forfreezing the water. Building design will generally call forinsulation similar to that used for cold storage. Thediscussion which follows is centered around an ice plantusing an ammonia system.

20-2. Plant Design and Layout. A permanent iceplant requires special construction of a building, as

illustrated in figure 30. You will see that part of the floorhas been omitted from the drawing. Below the floor is alarge tank which is filled with a brine (salt) solution. Theevaporator is a flooded type with the coil weaving backand forth between rows of ice can set in the brine tank.The floor above the tank has removable slabs. Look atthe left in figure 30; you can see where one of the slabshas been removed so that the ice can filler can be used tofill a fresh can with water. Just to the right, you can seewhere the hoist has been used to lift a can with a frozenblock of ice out of the brine tank. In the foreground, acan dump is illustrated. Warm water may be sprayedover the can to loosen the ice.

20-3. In figure 30 you can see an illustration of acompressor with a shell and tube condensing unit. Acooling tower would be necessary unless fresh water isvery plentiful. At the opposite corner of the room, youwill see the agitator motor. This motor circulates thebrine to increase the rate of transfer of heat between theevaporator coil and the ice cans. To the right of theagitator is the accumulator. This is a large vertical tankwhich extends down into the brine tank. It serves toprovide liquid ammonia to the bottom header of theevaporator. The ice storage room is not illustrated here;but in some plants, the overflow from the mainevaporator is used to cool the ice storage room.

20-4. Operating Principles and Application. Let usstart at the compressor for a brief review of the operatingcycle. Coming from the compressor is a hot gas underhigh pressure. The gas is cooled and becomes a liquid inthe condenser. At the float valve, the liquid passes into areduced pressure area-the evaporator-where it boils andabsorbs heat as it changes to a gas. From theaccumulator, the suction line returns low-pressure vaporto the compressor. The refrigeration cycle is illustrated infigure 31, where we have also shown the cooling waterpath through the tubing of the condenser and thecompressor heads. The temperature of the brine ismaintained at 15° F. This will free a 300-pound block ofice in 45 to 48 hours. At warmer brine temperature, thefreezing period becomes too long to be economical. Attemperatures colder than 15° F., the ice is too brittle andfractures easily.

20-5. There are three factors to make a good block ofice: (1) A brine at 15° F. has the lowest practicaltemperature which will make good ice. (2) The ice watershould be agitated continuously while the main part ofthe block is being frozen. This is done by means of asmall rubber hose which puts a jet of low-pressure airinto the water. The pressure is adjusted so that the hosepulses back and forth. This insures a good grade of clearice. (3) The core water should be sucked out and re-

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Figure 30. Layout of an ice plant.

placed by fresh water when the block is about two-thirdscomplete. The core water will have salts and otherimpurities concentrated in it, and the ice will have adisagreeable taste unless the core water is discarded.Also, the fresh water in the core will freeze faster thanthe water it replaces, so it is also a measure of economy.Let us consider next certain new components which arepeculiar to an ice plant.

20-6. Components. The usual accessories, such asstrainers, are just as vital in an ammonia system as in anyother similar system. Of more specific concern to youhere are such new components as ice cans, can fillers,agitators, core suckers, ice can hoists, dip tanks, and candumps. These are discussed, in the order named, below.

20-7. Ice cans. The ice cans used at an ice plant are allof the same size in order to standardize operation andhandling. Cans are made in different sizes, with thesmallest one capable of making a 50-pound block of ice.The largest cans are made to produce a block of iceweighing 300 pounds. The lifting arrangement at the topof the can must be standardized so that one hoistattachment will fit all of the cans.

20-8. Can fillers. A permanent type can filler uses atank of sufficient capacity and a float valve to shut offthe water automatically at the right level. The tank is

mounted on a raised platform higher than the top of theice can. When a can is placed under the tank, a dumpvalve is tipped and the ice can is filled with the rightamount of water. The water supply to the tank is shutoff while the dump valve is tripped. When the dumpvalve is shut off, the tank is automatically refilled. Aportable type of can filler is shown in figure 32. Youmust be sure that the float ball and trip level operateproperly to shut off the water when the ice can is full.

20-9. Agitators. The brine agitator consists of anelectric motor, a shaft, and an impeller. This motor runscontinuously to insure transfer of heat from the cans tothe evaporator. Another agitator consists of a small airpump and the necessary hose to reach the ice cans. Airis used to agitate the water during the early stages of iceformation to insure a good grade of ice.20-10. Core suckers. A core sucker is a pipe long

enough to reach the bottom of the ice can. A hoseconnects it with an injector or suction pump. The suckeris used to remove the core water, which contains aconcentration of salt and other impurities, after most ofthe ice block has formed. The core water is dischargedto the sewer system, and fresh water is added to fill thecore so that freezing of the block can be completed.This

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Figure 31. Refrigerant cycle and cooling water path.

operation insures purity of the ice and freedom fromobjectionable taste and smell.20-11. Ice can hoists. The can hoist is used to load and

unload ice cans from the brine tank. A small plant mayuse a portable band winch of the type you saw in figure30. A large volume plant usually has a rail-mountedoverhead hoist which can be moved to any position overthe brine tank. 20-12. Dip tanks. A large tank of water may be used to

free the finished block from the can. The can is loweredinto the tank, where it remains long enough to melt thesurface of the block. Tap water temperature may bewarm enough so that it is not necessary to add any moreheat to the dip tank.20-13. Can dumps. After the block is free, the can is

removed from the dip tank and placed on a dump rack.The rack tips the can at an angle to allow the ice to slideout. When a dip tank is not available, the ice can may bepositioned on the dump and warm water sprayed over thecan to loosen the ice.20-14. Ammonia System Operation and Maintenance.

The operation of an ammonia system requirestemperatures and pressures different from those forhalogens refrigerants. Also new to you is the makeup ofthe brine solution used in an ice plant.

20-15. Brine solution. If you have operated a car in acold climate, you know that an antifreeze solution insuresthat a liquid will remain liquid at below freezingtemperatures. Although glycol or alcohol can be used asan antifreeze additive, the most common additive is salt,which gives the name "brine" to the solution. A saltsolution may be checked for its freezing point with ahydrometer if the temperature of the solution is takeninto account. Four brine solutions and their specificgravity are given in table 9. The specific gravity is givenfor a solution temperature of 60° F. A sodium chloridesolution reaches its eutectic point at -6° F. Beyond thispoint, the addition of more salt will cause the solution tothicken.20-16. A brine solution made with 2 1/2 pounds of

calcium chloride to 1 gallon of water will not freeze at 0°F. Two pounds of ordinary table salt (sodium chloride)per gallon of water will freeze at slightly below 0° E A40-percent solution of alcohol is good at 0° F., while anethylene glycol solution requires about 45 percent glycolto inure that it will remain a liquid at 0° F. You willnote that any of the above solutions would be adequate,as a brine temperature of 15° F., can usually bemaintained with an evaporator temperature of 5° F

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TABLE 9

20-17. Ammonia temperatures and pressures. Let us firstdeal with normal operating conditions which you wouldexpect in warm weather. With a suction gauge pressureof 20 p.s.i.g., you should have an evaporator coiltemperature of about 5° F. A normal head pressure of185 p.s.i.g. should carry a vapor temperature of 238° F.Since temperatures approach 250° F., water jackets areused to cool the compressor head. At this head pressure,ammonia will condense at 96° F. In colder weather,head pressure may drop to 155 p.s.i.g., with thetemperature of the vapor dropping to 212° F. At a gaugepressure of 155 p.s.i.g., ammonia condenses at 86° F. Itis necessary to raise the operating pressure on the system.You may use a manual valve in the liquid line to throttlethe system. As pressure builds up, be sure to open thevalve and restore it to its normal operating position.20-18. Condenser cleaning. Even with proper treatment,

the tubes in a shell and tube condenser may accumulatescale. A temperature rise of 5° above normal incondenser output is an indication of scale formation. Wewill discuss next the most effective method for removingscale. The necessary equipment for cleaning is shown infigure 33. The drum or barrel should have a capacity of50 gallons. It may be wood, stone, porcelain, or metal.Galvanized metal must not be used, as it will react toofast with the acid used for cleaning. The fine meshscreen (bronze or copper) in the barrel serves to preventscale from entering the pump. Look at the position ofthe pump in the suction line and note how scale fromthe condenser will be held in the drum. The circulatorpump must be made of acid-resistant parts. The ventpipe provides a way of voiding hydrogen gas from thesystem. This gas is evolved as part of the chemicalreaction between the acid and the scale. Galvanized pipeor fittings must not be used in the setup.

20-19. Goggles, rubber gloves, and aprons must beworn while you are mixing acid or handling the solution.Furthermore, bicarbonate of soda (baking soda) should beimmediately available to counteract any spills orneutralize accidental skin burns. (NOTE. Always addacid to water when mixing, particularly sulfuric acid. Itgives off a large amount of heat, which the water canabsorb and dissipate. Avoid inhaling acid fumes as theycan easily damage mucous tissues.) An inhibited acidsolution is prepared by using commercial gradehydrochloric acid (muriatic acid) with a specific gravity of1.190. The solution may be prepared in the barrel usedwith the cleaning setup. Each 10 gallons of waterrequires that 3 2/5 ounces of inhibitor powder bedissolved in it. Add acid to this solution at the rate of 11quarts of acid for each 10 gallons of water. Commercialgrade sulfuric acid may be used if muriatic is notavailable, but the solution will not do as satisfactory a jobof cleaning the tubing.20-20. The inhibited acid should be circulated through

the tubes for about 12 hours to remove scale deposits ofaverage thickness. Cleaning time will be slower if thesolution is cold, whereas cleaning will be faster with a hotsolution. The strength of the solution may be checkedby applying a few drops to some baking soda. The rateof bubbling or gassing indicates how much strengthremains in the solution. When the solution becomesvery weak, there is little point in continuing to circulate itthrough the condenser. Be sure to flush out thecondenser tubing immediately after cleaning. Flush thecondenser tubes with fresh water until the dischargewater becomes clear. The effectiveness of the cleaningmay be indicated by the amount of scale deposited in thebarrel. The final measure, of course, is the return of thecondenser to normal temperature range during operation.

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Figure 32. Portable can filter.

Figure 33. Equipment setup for scale removal.

Review Exercises

The following exercises are study aids. Write youranswers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the test. Do not submit your answers for grading.

1. Where are the coldest rooms located in arefrigerated warehouse? (19-2)

2. Outside of the machine room you will findcertain areas which may be dangerous. Explainthe dangers in these areas. (19-4, 5, 8)

3. What will probably happen if potatoes are piledtoo high in storage? (19-8)

4. Modern methods of construction haveintroduced what two new basic fundamentals toa cold storage building? (19-10)

5. With modem construction of a refrigeratedwarehouse, to what should the vapor barrier beattached? (19-14, 15)

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6. How should you use the blueprint of a coldstorage plant? Give several uses and applications.(19-18-21)

7. What are details on a blueprint? (19-21, 22)

8. A cold storage plant has what operatingadvantages when four or more compressors areinstalled? (19-24)

9. What factor is used to determine the setting of asuction side pressure control which starts andstops the compressor motors? (19-24)

10. (True)(False) Evaporator coil temperature is amore reliable indicator of system operation thansuction pressure. Why? (19-24)

11. What are two ways of building up head pressureduring cold weather operation? (19-24, 25)

12. Describe the proper way to check a three-phasemagnetic switch for voltage. (19-24)

13. Where is dashput oil used? (19-24)

14. What test should you make of a motor whenyou install it? (19-24)

15. Your personal safety is at stake when you workon V-belt. What precautions must you observeto keep from injury? (19-24)

16. How should you treat V-belts which get splashedwith oil? (19-24)

17. How would you adjust the tension when one V-belt of a set shows a more pronounced flutterthan that of the others? (19-24)

18. How would you interpret a gradual drop in headpressure as compared with a sudden drop? (19-24)

19. What is the purpose of a recording chart? (19-24)

20. In an evaporative condenser what is the purposeof bleed-off water? (19-25)

21. How can bleed-off water affect the volume ofmakeup water? (19-25)

22. What is probably the best method of capacitycontrol of an evaporative condenser during coldweather operation? (19-25)

23. What are the main disadvantages of a coolingtower? (19-25)

24. What are the checks which should be made on awalk-through inspection of the freezer rooms ina cold storage plant? (19-27-29)

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25. What is a big advantage of a hot gas defrostsystem for a large evaporator in a zero coldroom? (19-30)

26. Why is an agitator necessary in the brine tank ofan ice plant? (20-3)

27. Why is the head of an ammonia compressorcooled with a water jacket? (20-3, 17)

28. What are three important factors in making agood grade of ice? (20-5)

29. Why is it necessary to use a core sucker? (20-5,10)

30. How is it that the brine solution is operated at15° F. but it is made up so as not to freeze at 0°F.? (20-15, 16)

31. How is inhibited acid prepared for cleaning scalefrom the tubes of a condenser? (20-19)

32. Why is baking soda necessary when you arecleaning scale with inhibited acid solution? (20-19, 20)

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CHAPTER 4

Special Application Systems

SOMETIMES we try to make things morecomplicated than they are. You can avoid confiningyourself if you keep in mind that a basic system ismodified to make it work for a special application. Yet,not one of the system’s basic principles is changed. Thischapter deals with multiple evaporators and multiplecompressors and concludes with systems for producingultralow temperatures. Technical information on thesesystems is reproduced from Commercial and IndustrialRefrigeration, by C. Wesley Nelson, copyright 1952,McGraw-Hill Book Company; used by permission. Youare already familiar with the name of items which will bediscussed, but differences result from the conditionsunder which this equipment operates. Let us considerfirst the problems of a system using several evaporators.

21. Multiple Evaporator Systems21-1. A multiple system is one in which several

evaporators are operated from one compressor. Avariation is the operation of two or more compressorswith one evaporator. Multiple units are installed inrestaurants, soda fountains, bars, and in other placeswhere more than one refrigeration fixture is used.Capacity control is obtained by using two or morecompressors for one evaporator. An example is an iceplant when the compressors are started or stoppedaccording to the load demand.

21-2. Classification of Multiple Evaporator Systems.Fundamentally there are only two classifications ofmultiple-unit systems. The first is the one in which allthe evaporators operate at the same temperature. This isthe simplest, although not the most common. Thesecond is the one in which the temperatures in thedifferent refrigerators are not the same. In order tocontrol the temperature in a multitemperature installation,various combinations of valves and controls must beused. The correct selection and installation of thesevalves and controls have a decided bearing on the successof the installation.

21-3. Cord Valves for Multiple Units. When two ormore evaporators are operated from the same compressorand the temperature of the warmer refrigerator is notmore than 5° F. higher than the colder, no special valvesare necessary. When the temperature difference isgreater than 5° F., some sort of valve or control for thewarmer refrigerator is essential. A thorough knowledgeof the operation and application of the types of availablecontrol valves is necessary before a satisfactory multiplesystem can be laid out.

21-4. Suction-pressure regulating valve. This valve, alsocalled an evaporator-regulating valve, is placed in thesuction line of the warmer evaporator, and controls itspressure (and consequently its saturation temperature) sothat it will remain substantially constant and not gobelow the predetermined setting of the valve. Thus,when two or more evaporators are operated with onecompressor, the desired temperature in the warmerevaporators can be maintained by the proper setting ofthe valve. The locations of the valves in a system areshown in figure 39. (See paragraph 21-19.)

21-5. Bellows type. A bellows type evaporator-regulating valve has the inlet connection from theevaporator and the outlet connection to the compressor.The evaporator pressure acting under the bellows and theforce of a small spring under the valve are both opposedby a spring. When the forces are equal, the valve is inequilibrium and maintains a definite opening. Areduction in evaporator pressure will cause an unbalancingof forces, and the valve will throttle. The resultingdecrease in the flow of vapor will prevent the pressurefrom going too low. The condensing unit continues tooperate on the other evaporators at reduced suctionpressure. This valve has a fitting where the evaporatorpressure may be taken. A gauge adapter valve must beused. The cap is removed and the adapter is screwedonto the fitting with the key engaging the needle valve.The gauge is connected to the

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Figure 34. Method of bypassing evaporator-regulating valve.

adapter and, when the valve is opened, the pressure maybe read. This fitting is also used in pumping down theevaporator. The regulating valve must be bypassed whenpumping down, because it would close on reduction ofsuction pressure. To bypass the valve, a line is run fromthe adapter to the compressor’s suction-valve gauge port.If the distance is too great, a connection should beprovided on the compressor side of the valve, as shownin figure 34.

21-6. Diaphragm type. Another type of evaporator-regulating valve is illustrated in figure 35. This valve hasa diaphragm instead of a bellows. One of the features ofthis valve is the collar with pressure graduations underthe adjusting knob. By turning the knob until the bottomlines up with the graduations, you can make the correctsetting without reading the pressure or without waitingfor the refrigerator to arrive at the desired temperature.The operation of this valve is similar to the onepreviously described in that the valve remains open whenthe warmer evaporator pressure is high and then throttlesas the compressor lowers the pressure. This valve has agauge port for checking pressure and for bypassing. Toget a reading, you attach the gauge to the port, removethe cap, and open the gauge shutoff valve. The valverange is from 40 p.s.i. to 0 in. Hg vacuum, and it can beused on Freon units up to 1/2 ton and up to 3/4 ton onmethyl chloride and SO2 units.

21-7. Two-temperature type with manual closing. Stillanother type of two-temperature valve is the one shownin figure 36. You adjust this valve by the adjusting nut;the handwheel is used only for closing the valve withoutaffecting the setting. You use the auxiliary valve whenattaching a gauge. You may also use it to bypass themain valve when you want to pump out the coil. Duringnormal operation, the auxiliary valve is closed, and whenthe coils being evacuated, the valve is turned intomidposition. The valves men-

(Courtesy Controls Company of America)Figure 35. Diaphragm type evaporator-regulating valve.

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Figure 36. Two-temperature valve with manual closingarrangement.

tioned above should be installed in a location wherefrosting will not occur and should be reasonably close tothe refrigerator which is to be controlled. These valvesmay be used on flooded or direct-expansion evaporators,providing defrosting is not required.

21-8. Snap-action type. A suction-pressure regulatingvalve of the snap-action type is not a throttling type andcan be set to cut in and out at definite predeterminedpressures. This valve is either wide open or closedtightly. You use it when you want to operate anevaporator on a defrosting cycle, and when a shorteroperating time than that provided by the condensing unitis required. The effect of using a snap-action valve on anevaporator in a multiple system is the same as if it wereconnected to a separate compressor. This valve shouldbe used only with a low-side float or with a thermostaticexpansion valve. Most valves of this type have a gaugeport to which a gauge may be attached to aid the propersetting.

21-9. Thermostatic type. A thermostatically controlledsuction-pressure valve is shown in figure 37. This valveis used where close, nonelectrical control of singleevaporators is desired. Such applications are sweetwaterbaths, water coolers, beverage coolers, and sodafountains. In multiple installations, you place the valvesin the suction line from the warmer evaporator, with thethermal bulb in the refrigerated space or liquid. Thisvalve gives closer temperature control than does thepressure type. The valve illustrated in the figure is of thesnap-action type, but the thermostatic type is alsoavailable in a valve which has throttling action. Beforethe refrigerator has reached the desired temperature, thevalve is wide open and the coil is subject to refrigerationfrom the condensing unit. When the desired temperatureis reached, the valve snaps shut and the coil is isolatedfrom the rest of the system. If the refrigeratortemperature is above freezing, the coil will defrost whilethe valve is closed. You must install this valve in ahorizontal part of the suction line, and place a strainerahead of it. The bulb should be located where it willreflect the average conditions, and in water baths itshould be placed in the liquid but not too close to thecoils.21-10. Check valves. When evaporators are connected

in multiple and the temperatures are different, thepressure in the warmer evaporator is higher than that inthe colder. When the control valve opens, the high-pressure vapor in the

Figure 37. Thermostatically controlled suction-pressure valve.

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warmer evaporator would back up into the colderevaporator if no means were provided to prevent it. Thisvapor would cause a warming up of the colder evaporatorand would impair its efficiency. To prevent this, youinstall a check valve which will permit the vapor to flowin only one direction. See figure 39 for the properlocation of check valves in a multiple system. Next, letus review some important points before discussing theuse of solenoid valves in a multiple system.21-11. Important Points for Multiple Installations.

Because of the large number of possible multiplecombinations, it is impossible to give a set of rules andexpect them to apply to all cases. Although there areexceptions to the rules, the eight rules explained nextshould be adhered to whenever applicable.

(1) The coldest evaporator or evaporators mustcomprise more than one-half of the total load on thecondensing unit. If the warmer evaporator were themajor part of the load, the condensing unit would beoperating at the higher suction pressure a greater portionof the running time and would not be able to bring thecolder refrigerator down to the desired temperature.

(2) The capacity of the condensing unit is selectedat the suction temperature or pressure of the colderevaporator. Since the colder evaporator constitutes themajor part of the load, the compressor will be operatingat its pressure most of the time, although the pressure inthe warmer refrigerator will be higher. This is anothercase where we must remember that the capacity of acompressor is less at lower suction pressures.

(3) The evaporator for each refrigerator is selectedat the suction pressure which will give the correcttemperature and humidity for the particular application.The selection is made just as if each evaporator were tobe connected to its own compressor.

(4) When the temperature difference between thecolder and the warmer fixture is greater than 5° F., acontrol for the warmer evaporator or evaporators isnecessary. This control may be either a suction valve ofthe pressure or temperature type or a solenoid valve. Insome cases, although the temperatures are the same, onerefrigerator will be used much more than the other. Ininstances like this, a control valve should be used andplaced in the suction line of the refrigerator with the leastusage.

(5) A snap-action type of suction-pressure controlshould be used if defrosting on the off cycle is required.This cannot be done, even though a snap-action valve isused, unless the refrigerator temperature is above 35° F.

(6) The coldest evaporator should always be directlyconnected to the compressor, and a check valve should

be located in the suction line between the outlet and thefirst takeoff. In following the rule that half of the totalload should be the cold evaporator, there is sufficientload on the compressor to eliminate low back pressureeven though the control devices have isolated all thewarmer evaporators.

(7) In general, thermostatic expansion valves shouldbe used as the liquid control when direct expansionevaporators are installed in multiple. The control oftemperature in any refrigerator should not be by theadjustment of any expansion valve. This should be doneby the adjustment of the suction-pressure valve in orderto obtain the best operating conditions.

(8) The liquid and suction lines should be sizedaccording to the amount of refrigerant flowing andaccording to the load on each branch or main. Theseimportant points place a limitation on the applications inwhich a multiple installation should be made. When thetemperature difference between the warmer and thecolder refrigerators is greater than 25° F., multiplexingshould be considered the exception rather than the ruleunless humidity is not a factor. When high humiditiesare to be maintained, such as in florist's boxes, it is betterto use a compressor for each evaporator.21-12. Evaporators with forced convection. Although

multiple installations can be made with all expansioncoils, all low-side float coils, or with a combination ofboth, you must give extra thought when you want to useforced-convection coolers. A forced-convection unitmust be caused to defrost during the OFF cycle unlesssome means for artificial defrosting is provided. In somemultiple installations where the forced-convection unit isthe colder evaporator, a sufficiently low suction pressuremay occur so that the unit cannot defrost, and it thusbecome inoperative in a short time. If the forced-convection unit is the colder evaporator, successfulmultiplexing may be done if suction-control valves areused.21-13. Low-pressure cutout. Multiple installations, where

suction-pressure or temperature-control valves are used,have the colder refrigerator controlled by the low-pressurecutout at the condensing unit. The warmer refrigerator,in this type of arrangement, does not require anyelectrical control. The low-pressure electrical control isset at the proper cut-in and cut-out points just as if itwere operating on a single evaporator. Some of themodern suction-control valves that are used on thewarmer evaporators are calibrated so that the temperaturesetting can be made in advance. If this is not so, youmust operate the system until the refrigerators come

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down to the desired temperature; you then adjust thecontrol to shut off the evaporator from the compressor atthis point. In any event, the final adjustment of thecontrols is governed by the thermometer readings in thevarious refrigerators.21-14. Solenoid Valves in Multiple Systems.

Solenoid valves are used extensively in a multiple system.They may be placed in either the liquid line or thesuction line. Figure 38 shows a multiple hookup usingsolenoid valves in the liquid line. As may be seen fromthe diagram, there is a thermostat in each refrigerator,and each thermostat is connected to the solenoid valvethat is in the liquid line leading to its refrigerator. Theoperation of the system is as follows: Assume that all thethermostats call for cooling and that the compressor isoperating on all of the evaporators. When onethermostat is satisfied, it opens the circuit and thesolenoid valve closes the liquid line to the evaporator.The compressor pumps out the refrigerant from thatevaporator and continues t operate on the others. Aseach thermostat is satisfied, its solenoid valve closes; andfinally, when all valves are closed, the compressor isstopped by a low-pressure cut-out.21-15. There are several important factors that must be

considered in connection with multiple systems usingsolenoid valves. As each solenoid valve closes, its

evaporator is pumped out and the refrigerant is returnedto the receiver. The receiver, therefore, must be largeenough to hold the entire charge in the system. Whenthe compressor is operating on all the evaporators, it is atfull load and the suction pressure is high. As oneevaporator after the other stops refrigerating, the suctionpressure drops progressively lower. This drop in suctionpressure has the disadvantage of continually upsetting thebalance between the refrigerator temperature and the coiltemperature. The result affects the humidity in the boxand, in some cases, prevents the defrosting of the coil. Asuction-pressure regulating valve placed in the suction linenear the compressor will hold the pressure at the desiredpoint in the evaporation although the crankcase pressurewill be low when only one evaporator is operating fromthe compressor. The low-pressure control, which shutsoff the compressor after the last solenoid valve closes,must be set lower than the suction pressure when thecompressor is operating on only one evaporator. Thesetting of the cut-in point should be made so that theopening of one solenoid valve will start the compressor.21-16. Solenoid valves that are used in the suction line

from the evaporator should be selected so that thepressure drop through the valve will not be over 2 p.s.i.When a solenoid valve is so used, the refrigerant remainsin the

Figure 38. Multiple system using solenoid valves.

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coil and does not return to the receiver. If the valve isplaced in the suction line, there is danger of accumulatedliquid flooding over into the compressor in the event of aleaking float or expansion valve.21-17. Installation. A multiple system is installed like

a simple one insofar as the coils and condensing units areconcerned. In order to simplify service operations, amanifold is usually placed on the wall near thecondensing unit. Three-way valves are sometimes usedto allow the refrigerant to pass through the valveunobstructed on the run of the valve, while the branchline from the side outlet may be shut off. Prefabricatedmanifolds may also be obtained.21-18. Evaporators at same temperature. When the

temperatures are the same in all of the refrigerators, thereis an expansion valve on each coil. When two coils arelocated in the same case, it is not good policy to connectcoils in series, because the second coil will not maintainits rating. Two coils should not be connected to oneexpansion valve, regardless of whether they are in seriesor parallel. There are no pressure-control valves neededwhen all evaporators are operated at the sametemperature. The entire low side of the system iscontrolled by a low-pressure control located on the baseof the compressor unit.

21-19. Evaporators at different temperatures. The linediagram in figure 39 shows the connections for threecoils at different temperatures. Note the presence of asuction-pressure control valve in each of the warmercoils. The suction line from the coldest evaporator isdirectly connected to the compressor with a check valvein the line. In this diagram, the -10° evaporator shouldconstitute the major portion of the load. A check valveis also found in the suction line from the 35° evaporator,since this evaporator is colder than 45° and there wouldbe the possibility of the warm vapor backing up andcondensing,

22. Multiple Compressors22-1. Compressor units are sometimes connected in

parallel to obtain greater flexibility or to use small unitson one evaporator where a larger one that will balanceproperly is not obtainable. The practice of operatingcompressors in multiple is not new; in fact, it is quitecommon in ammonia plants and cold storage warehouses.The principle difficulty in interconnecting condensingunits is in the oil return to the crankcase. Ammoniadoes not present any problem in this regard, since oil andammonia are not miscible. Freon, methyl chloride, andother oil-miscible refrigerants, on the other hand, presenta real difficulty when condensing units that use them are

Figure 39. Multiple systems using evaporative-regulating valves.

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Figure 40. Balanced lines between compressors.

interconnected. Multiple installations of condensing unitsshould be avoided and made only when it is not possibleto split up the units that each evaporator has its owncondensing unit.

22-2. Connections Between Compressors.Compressors that are to be interconnected should be ofthe same manufacture and preferably of the same size.A good installation is one in which each condensing unitwill carry its share of the load and the oil return will besuch that the proper level will be maintained. To get thisbalance of the load, the liquid, suction, and dischargelines are interconnected and it is necessary that oil- andgas-equalizer lines are installed between the crankcases.The compressors should be placed close to each other sothat the connecting lines will be as short as possible.

22-3. Balanced refrigerant lines. Lines should beconnected as shown in figure 40 so that the elbows andlength of pipe from the tee to one compressor are the

same as to the other compressor. Thus the frictionalresistance between each receiver and the manifold shouldalso be approximately the same. Both suction anddischarge lines should be balanced in the same manner aswe have just described. Suction lines should beconnected so that the oil which is returning through theline will divide between the compressors as evenly aspossibly. Suction lines from a manifold to thecompressor, if used, should be taken off at the side tofacilitate oil return.

22-4. Oil-equalizer line. The crankcase oil-equalizerline may be connected in one of two ways, A or B, ashown in figure 41. The A method is preferablealthough the B method is more often used because of thelocation of plugs in the crankcases of some compressorswhere the equalizer lines may be connected. In themethod shown in A, the oil-equalizer connection shouldbe made at the lowest safe oil level. Condensing unitsshould be placed on their foundations so that the oil levelin each is in the same horizontal plane. The gas-equalizer connection is made above the maximum oillevel. All equalizer lines should be level. The size of themanifold to which the various branches are connectedshould be at least equal in area to the sum of thebranches. Crankcase oil- and gas-equalizer lines shouldbe not less than 3/4-inch ID up to 10 tons capacity and l-inch ID over 10 tons.

22-5. Control of Multiple Compressors. Whencondensing units are interconnected for purposes ofcapacity control, usually you have to provide a means forstarting and stopping the compressor according to loaddemands. The compressors are manually operated onlywhen an operator is in attendance and when load changescan be anticipated beforehand. For liquid or air cooling,if close temperature control is not required,

Figure 41. Oil equalizer lines.

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two temperature controls may be used, one being set adegree or two higher than the other. A more commonmethod is to use pressure controls on the commonsuction line, set in sequence so that the compressors willstart and stop according to changes in suction pressure.When this method is used, thermostats and solenoidvalves are almost always installed.

22-6. When a number of compressors are connectedtogether or when an installation consists of a number ofsingle evaporator and condensing-unit installations in onerefrigerated space, situations occur in which allcompressors will start at the same time. This puts a veryheavy load on the electric lines and power system. Atimer, which will delay the starting of compressors untilafter the first one, should be installed. The action of thetimer is such that when the contactor for the firstcompressor has closed, there is a delay of 10 or 15seconds before the timer closes the control circuit of thesecond compressor and allows it to start. If there aremore than two compressors, a timer may be used oneach except the first one.

23. Ultralow Temperature Systems23-1. The use of ultralow-temperature refrigeration in

industrial work has increased tremendously in the pastfew years. Commercial units are now manufactured toproduce temperatures below -100° F. for variousapplications. An example is the production testing ofvarious instruments and appliances, such as radios,cameras, clocks, and meters which may be subject to lowtemperatures in arctic climates or in outer space.Ultralow temperatures find application in various kinds ofmetal treatment. The hardness of certain kinds of steelshas been materially increased after a conventionalhardening process by lowering the temperature to about-110° F., allowing them to warm to room temperature,and then tempering. Another development is the shrink-fitting of parts by using cold instead of heat. The malepart is reduced in temperature to -100° F., after which itis fitted to the female part and the unit allowed to warmto room temperature. The extensive use of aluminumriveting in aircraft and other metal work has led to theuse of special alloy rivets which may be prevented fromage hardening and kept soft by holding them at -40° to-45° F. until ready for use.

23-2. Test chambers which are designed for simulatingconditions encountered by military and other aircraft arebeing used increasingly. They are used for testinginstruments, clothing, military weapons, and equipmentthat is normally carried in an airplane. Weather bureauinformation shows a temperature of -50° to -60° F. at

elevations around 50,000 feet, and cabinets for testing areusually kept between -60° and -70° F. Some cabinets areequipped so that any temperature from +100° to -100°F. may be obtained.

23-3. Insulation Requirements. Ultralow-temperaturecabinets require more consideration in regard toinsulation and construction than do zero cabinets.Insulation thicknesses of 10 and 12 inches are needed,and extra care must be taken with vaporproofing toprevent the entrance of moisture. When a refrigerator isintended to maintain a low temperature at all times, it isusually desirable to use an insulating material which has ahigh thermal capacity such as cork. Any interruption inrefrigeration will not be so serious because of the slowwarming up of the box. On the other hand, when rapidfluctuations in temperatures are desired, such as insimulated flight, an insulation of low heat capacity shouldbe used. Ferrotherm (a number of thin steel sheets withair spaces) and Santocel (silica aero-gel) are two suchinsulating materials. Tests at Wentworth Institute usingdry ice in a box insulated with nine sheets of Ferrothermwith 36-inch air space between the sheets gave atemperature reduction from +70° to -70° F. in 45minutes.

23-4. Refrigerant and Compressor Problems. Asimple refrigeration cycle is neither suitable noreconomical for ultralow-temperature application. In orderto obtain heat extraction from a box at a temperature of,say, -70° F., it is quite evident that a coil temperature lessthan -70° F. is necessary. If a 10° F. temperaturedifference were assumed, a design temperature of -80° F.for the coil would be used. If Freon 12 were therefrigerant selected, the corresponding absolute pressureand volume would be 2.885 p.s.i.a. and 11.57 cubic feetrespectively. This would give a compression ratio of over30 to 1 with normal condensing temperatures. This ismuch higher than is possible with a conventionalcompressor. As a matter of fact, a compressor operatingwith any such ratio would not discharge vapor but wouldsimply compress and expand the vapor in the cylinderwithout doing any useful work. The compression ratiofor units working under average commercial conditions isapproximately 4 to 1. Ratios up to 8 to 1 are consideredas being satisfactory for a single compressor. Whenratios are above these values, because of extremely lowtemperatures, you must employ staging in order that therewill be less work required per ton of refrigeration.

23-5. Staging. In a simple compression system, theheat that is absorbed at the low level of temperature isrejected at a higher level in one

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step. In a low-temperature application where this iseither impossible or impractical, the heat may be"pumped" in two or more steps. This is called staging.Staging may be done by two methods in refrigerationwork: (1) by using compound compression in which thevapor is removed from the evaporator by the low-pressurecompressor and discharged by it to the high-pressurecompressor, which discharges to the condenser in theusual manner; (2) by using an arrangement calledcascading which is, in effect, two cycles operating atdifferent heat levels. The low-pressure compressordischarges into a condenser which is the evaporator forthe high-pressure cycle. The final heat is rejected to thecooling water as in the simple system. In direct stagingthe same refrigerant is used throughout, while in thecascade system different refrigerants may be used in thehigh- and low-pressure stages.

23-6. Compound Systems. Although a compoundcompression system consists essentially of two or morecompressors in series, the addition of intercoolers andsubcoolers will increase the efficiency and reduce the costof operation. Of the several arrangements, two of themost common, the direct compound and the cascadesystems, are included here.

23-7. Direct compounding. Direct compounding withan intercooler is illustrated in figure 42. This is a two-stage compression in which the refrigerant vapor is drawn

from the evaporator through the heat exchanger by thefirst-stage compressor. The discharge from thiscompressor passes through a water-cooled intercooler,which is located between stages, and from there to thesuction of the high-pressure compressor (second stage).The vapor is then liquefied in the condenser and flowsthrough the other side of the heat exchanger to theexpansion valve. The use of an intercooler reduces thesuperheat and the work of compression. The pistondisplacement of the low-pressure compressor is greaterthan that of the high-pressure compressor because of thegreater volume of the vapor at low pressure. The propersizing of the high- and low-pressure cylinders is such thatthe desired capacity will be obtained, and thecompression ratios for each compressor will beapproximately the same and within reasonable limits.When two individual compressors are used, they shouldbe at the same level, and oil-equalizer lines between themmust be provided as shown in the illustration. Theintermediate pressure which exists between stages is notcontrolled and will fluctuate within small limits as theload varies.

23-8. A compound compression system with a liquidsubcooler is shown in figure 43. The colder therefrigerant when it enters the expansion valve, the lessflash gas will be formed when the refrigerant cools downto the evaporator

Figure 42. Direct compounding with an intercooler.

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Figure 43. Direct compounding with a subcooler.

temperature. The purpose of the subcooler is to subcoolthe refrigerant and thus increase the refrigeration effect.Referring to the diagram, you see that the liquid leavesthe condenser, and a potion of it expands in thesubcooler coil at the suction pressure of the high-pressurecompressor. The remainder, at a much lowertemperature, leaves the subcooler and goes to theexpansion valve. What actually happens here is that theflash gas generated in the coil of the subcooler need onlybe compressed in the high-pressure compressor. Thevapor has a smaller volume at this intermediate pressure,and for these reasons, a considerable amount of workmay be saved. Without the subcooler, the flash vaporwould have to be compressed from the evaporatorpressure, where the volume is high, through both thefirst- and second-stage compressors. This arrangement,or one which will attain similar results, is a necessity inultralow-temperature refrigeration. In place of singlecompressors, a V-design of a compound compressor isused in smaller size units. This type of compressorrequires only one motor and eliminates the problem ofoil level equalizing.

23-9. Cascade systems. A cascade system consists oftwo or three separate simple cycles operating inconjunction with each other at different temperaturelevels. The connecting point is a heat exchanger betweenthe stages. This interstage heat exchanger is the

condenser for the first stage and the evaporator for thesecond stage. An elementary diagram of a cascadesystem is shown in figure 44. Beginning with the low-pressure cycle, the vapor from the evaporator iscompressed in the first-stage compressor and goes to theinterstage heat exchanger, where it gives up its heat tothe second-stage evaporator coil. The condensed liquidthen flows to the first-stage expansion valve and theevaporator, completing the low-pressure cycle. The vaporwhich is generated in the coil in the heat exchangerbecause of the heat it has absorbed is compressed in thesecond-stage compressor, and the high-pressure vapor iscondensed, its heat going to the cooling water. Eachstage is an independent simple cycle, and for this reasonhas some advantages over the compound compressors.There is no problem of oil equalizing, and a differentrefrigerant may be used in each stage. There is some lossin the cascade system because a temperature differencemust exist in the heat exchanger in order that the heatfrom the first stage will flow into the second stage. Atthe present time, the use of Freon 22 in the low stageand Freon 12 in the high stage will produce temperaturesdown to -90° F.23-10. A two-stage cascade system with a second heat

exchanger for subcooling the liquid and with an oilseparator in the discharge of the first

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stage compressor is show in figure 45. There are anumber of variations of this arrangement as far as thelocation of the second heat exchanger is concerned. Theinterstage heat exchanger, however, is always located inthe same place- between the two stages.23-11. Refrigerants for Compound Systems. At the

present time, the number of refrigerants that are suitablefor ultralow-temperature applications are few. Of thecommon refrigerants, ammonia SO2, methyl chloride, andCO2 are not used. Ammonia and methyl chloride havehigher specific volumes than either Freon 12 or Freon 22,and SO2 has a freezing point of -98° F., in addition to ahigh boiling point. Carbon dioxide becomes a solid whenit expands to a temperature below -70° F. Freon 12 andespecially Freon 22 possess the best characteristics forlow-temperature applications. The condensing pressure ofFreon 12 at 80° F. is 98.76 p.s.i.a., whereas for Freon 22it is 159.7 p.s.i.a. Compressors designed for Freon 12 mayordinarily be used with Freon 22, but in the large sizesparticularly, compressors designed for Freon 22 should beused. The displacement of the compressor is les forFreon 22 than it is for Freon 12. Therefore a Freon 12compressor would have a greater capacity when usingFreon 22 than when using Freon 12. Under someconditions, then, a larger motor would be required whenusing Freon 22. In systems under 10 h.p., other partssuch as liquid and suction lines would be the same as for

Freon 12. Ethane, ethylene, and methane arehydrocarbon refrigerants which are occasionally used inapplications where the temperatures are below -100° F.These refrigerants are explosive and are, therefore,unacceptable where there would be a hazard. Freon 13 isa refrigerant which is replacing the hydrocarbons forultralow temperatures. All of the low-boiling-pointrefrigerant have high head pressures, and pressure-reliefvalves must be provide wherever they are used.23-12. Controls. In an ultralow-temperature system,

the flow of refrigerant to the evaporator may becontrolled either by an expansion valve or by a floatcontrol. Ordinary expansion valves are not suitablebecause excessive superheating at the bulb location isnecessary to operate the valve. A differential-temperatureexpansion valve designed for ultralow application has twopower element operated by thermal bulbs. When anexpansion valve is used, a solenoid valve is always placedahead of it, and the coil is pumped down at the end ofthe running cycle.23-13. The high-side float is used quite extensively and

is simple and inexpensive. When used with anaccumulator, the charge is not too critical, and since thefloat valve is in the high side of the system, any moistureis less subject to freezing.

Figure 44. Elementary cascade system.

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(Copyright 1952. McGraw-Hill Book Company. used by permission.)Figure 45. Two-stage cascade system.

23-14. There are various ways to wire the controls in acompound compression system, depending on theparticular application. In a system which consists of onecondensing unit and one evaporator, the simplestarrangement is to use a solenoid valve and a low-pressurecutout with a temperature control in the refrigeratedspace. The temperature control actuates the solenoidvalve, and the pressure control operates the compressor.A special cutout must be used since the conventionaltools are not satisfactory for vacuums over 20 inches Hg.Design of these control circuits should consider overloadprotection because of heavy loads and excessive pressureswhich occur during pulldown. The electrical controls forcascade systems consist fundamentally of a set of controlsfor each cycle.23-15. Lubricating Oil for Low Temperature. It is

very important that the lubricating oil which is to be usedfor low-temperature applications be an oil from which nowax will separate at or below the lowest expectedoperating temperature. The Freons as well as otherchlorinated refrigerants possess solvent-extractionproperties which remove wax from oil. With arefrigerant-oil mixture, there are two conditions whichbring about wax separation. These are low temperatures

and a high percentage of oil in the mixture. The use of ahigh-grade oil which has been processed especially forlow-temperature refrigeration and the use of oil separatorswill minimize if not eliminate wax formation.23-16. An expansion valve or other refrigerant control

in which there has been wax formation acts somewhatlike one in which moisture has frozen. With waxformation, the valve will "let go" at a temperature lowerthan 32° F. if heated. Also, if the valve is taken apart,the wax may be seen in the orifice or at the outlet. Suchconditions would indicate that a poor grade of oil hadbeen used in the system.

REVIEW EXERCISES

The following exercises are study aids. Write youranswers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the test. Do not submit your answers for grading.

1. How is capacity control obtained in a largesystem with a variable heat load? (21-1)

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2. Give two applications of multiple evaporatorsystems. (21-2)

3. Name five type of evaporator-regulating valves.(21-4-9)

4. Where are check valves installed in multipleevaporators at different temperatures? (21-10)

5. Why must the coldest evaporator make up morethan half of the heat load? (21-11)

6. With multiple evaporators at differenttemperatures, which evaporator will becontrolled by a low-pressure cutout at thecompressor? (21-13)

7. How is the size of the receiver affected in amultiple evaporator system with solenoid valvesin the liquid line? (21-15)

8. What is the possible danger to the compressorwhen solenoid valves are used in the suctionline? (21-16)

9. What is the main difficulty with compressorsconnected in parallel? (22-1)

10. What are the installation requirements forsatisfactory operation of compressors in parallel?(22-2)

11. What two equalizer lines are necessary forproper lubrication of multiple compressors? (22-4)

12. In the case of multiple compressors, what isdone to reduce heavy electrical loads on starting?(22-6)

13. List two applications of an ultralow-temperaturesystem to Air Force problems or testing. (23-2)

14. What is the main requirement of an insulationfor an ultralow-temperature chamber whichmust respond to rapid changes in temperature.(23-3)

15. What are two methods of “staging” to produceultralow temperatures. (23-5)

16. Describe a direct compound system which hasgood efficiency. (23-6, 7)

17. Why may two different refrigerants be used in acascade system? (23-9)

18. Name three refrigerants used for ultralowtemperatures. (23-11)

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19. Why is an ordinary expansion valveunsatisfactory at ultralow temperatures? (23-12)

20. Why is a special cutout necessary for ultra-lowtemperatures? (23-14)

21. How is wax prevented from causing trouble inan ultralow-temperature system? (23-15)

22. How can you tell the difference between waxand moisture as the cause for a frozenexpansion valve? (23-16)

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CHAPTER 5

Vehicle Refrigeration Units

FROM MARKET TO warehouse and fromwarehouse to dining hall, refrigerated Air Force truckstransport many tons of perishable foods safely withoutrisk of spoiling. The safe delivery of these foods isdependent on the operation of refrigeration units. Part ofyour job is proper maintenance of truck-mounted units toinsure the delivery of good food to all the troops. Thischapter discusses the units for truck refrigeration and carcooling.

24. Refrigeration Unit for Trucks24-1. Since trucks and semitrailers transport perishable

or frozen foods long distance, they require some type ofrefrigeration. Refrigeration units for trucks andsemitrailers are of the same type, design, and size as unitsused in reach-in and walk-in refrigerators. Specificationswill depend on the demand.

24-2. Refrigerator trucks and semitrailers havespecially designed bodies adapted for the transportation ofmaterial under refrigeration. These bodies are designedwith a double wall or shell, with Fiberglas insulationbetween them. The refrigerator unit is installed where itwill give the best circulation of refrigerated air for thedemand. The source of power and control operation ofthe condensing unit and engine will be explained in thefollowing section.

24-3. Types of Units. The refrigeration units usedtoday are called package units. In such a package unit,the refrigeration unit, gasoline engine, starter-generator,and battery are all mounted on one frame as a single self-contained unit. Older type units may, however, have thegasoline engine and the starter-generator mounted on aseparate frame with a belt to the compressor.

24-4. There are two types of compressor drives whichget their power from the truck's engine: (1) the engine-driven electric generator and motor and (2) thetransmission shaft-driven compressor. If either of thesetypes is used, the refrigeration unit stops when the truckengine stops, thus requiring an outside source ofrefrigeration during layovers.

24-5. On the other hand, the package type gasoline-engine-driven units are automatically controlled to startand stop as the system may require. The space, oropening for the refrigeration unit, is designed for thedemand, as are the special bodies. Both the size of thebodies and the type of material to be under refrigerationdetermine the type, size, and number of refrigerationunits to be installed.

24-6. Installation. Refrigeration units for trucks andsemitrailers are usually mounted on the front of thebodies, either at the top or bottom. When the unit ismounted other than on the front, the trailer may have arack or platform designed for the purpose, as well asmounting bolts to secure the unit to the trailer body.

24-7. Power Connections. Power is furnished by agasoline engine, which is usually of the 2-cylinder, 4-cycle, L-head, air-cooled type. This engine is equippedwith a 12-volt, d.c., combination starter-generator, withthe armature mounted on the engine crankshaft. Theengine is started electrically by the power from two 6-voltstorage batteries, connected in series, that are mountedon the front of the truck or trailer body near therefrigeration unit. Most of these engines are governorcontrolled so that the engine runs at a speed of 2400r.p.m. This speed will give a maximum horsepower of9.4. The power is transmitted from the engine to theevaporator blower, the condenser fan, and the compressorby the use of V type belts and pulleys. The compressor isset to run at 1800 r.p.m. when engine speed is 2400r.p.m.

24-8. Starting Procedures. The starting proceduresare the same for most truck refrigeration units. Afterchecking for leaks, valve settings, compressor oil level,engine oil, and fuel level, etc., turn the refrigeration unitthermostat until the pointer indicates the temperature tobe maintained within the truck or semitrailer. Then setthe heat-cool switch to the cool position. (NOTE: Someunits have an electric heating coil mounted

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in the evaporator blower which is used in therefrigeration system to cool the trailer. The blower forcesair across the heating coil surfaces to raise thetemperature in subzero weather. On other units thecooling element of the thermostat is bypassed when theheat-cool switch is on HEAT. The heating element ofthe thermostat completes the circuit to start the engineand to energize the defrost solenoid valve. When thedefrost valve opens, hot refrigerant gas is permitted toflow to the evaporator to provide heat, which will raisethe temperature a few degrees above freezing inside thetrailer.)

24-9. Electrical Circuit Operation. The starterswitch is turned to the ON position in order to close thecircuit and energize the thermostat, which operates thestarter-relay coil. This action set up a magnetic field thatattracts the relay contractor bar to complete the circuit tothe starter-generator. When the relay circuit is opened orbroken, the relay coil is deenergized, and the contact barsprings away from the coil and opens the circuit to thestarter-generator circuit. This stops the engine. Thethermostat bellows expands or contracts with thetemperature change at the feeler bulb to automaticallyopen or close the contacts of the switch within thethermostat. In turn, the opening or closing of this switchopens or closes the circuit to the starter-relay coil.24-10. When the starter-relay closes, it also completes a

circuit to the choke-solenoid relay. This relay armaturecloses the contacts that operate the automatic choke andthe defrost solenoid valve. When the engine starts, thecurrent flowing through the choke-solenoid relay reversesdirection and decreases in magnitude so that the relay isdeenergized. This releases the relay armature and opensthe contacts to the automatic choke and the defrostsolenoid valve.24-11. When the automatic choke coil is energized, it

attracts an armature lever attached to the carburetorchoke valve by a linking rod. When the lever is drawn tothe magnetized coil, the carburetor choke valve closes.As the engine starts, a reverse flow of current is set up inthe choke-solenoid relay circuit, and the relay contactpoint break the circuit to the automatic choke.24-12. The starter-generator has a charging rate resistor

placed in the generator field circuit to regulate thegenerator charging rate, which is controlled by the voltageregulator. As the batteries near a fully charged state,voltage in the field circuit of the voltage regulator rises.At 17 volts, magnetism created by the regulator windinginsufficient to pull the armature down. This opens thecontacts of the normal control circuit, causing the current

to flow through the resistor in the field circuit andforcing the generator to operate at a minimum output.24-13. The defrost thermostat is energized when the

defrost switch is pressed and completes the circuit to thedefrost holding relay. This permits an increase in theevaporator coil temperature to 50° F. This temperatureincrease causes a bimetallic disk in the thermostat to snapto a reverse position. The thermostat switch contactsopen and deenergize the defrost holding relay. This lastaction returns the refrigeration unit to its normal coolingcycle.24-14. Operational Check. All of the controls which

we have been discussing operate automatically, except thestarter switch, the heat-cool switch, and the defrostswitch. Also, the gasoline gauge registers continuallywhen the starter switch is on.24-15. Blast Chilling. The technique known as blast

chilling saves time, investment, and fuel. In blastchilling, liquid carbon dioxide or nitrogen is injected intomechanically refrigerated trucks, resulting in quickcooling. Paragraphs in this section identified by anasterisk (*) are in part reprinted from January 1964Refrigeration Service and Contracting by permission ofNickerson and Collins Company.24-16. Do not confuse this type of cooling with total

truck refrigeration by liquid CO2 throughout the run. Wewill discuss total liquid CO2 cooling later in this chapter.Blast chilling is used at maximum cooling demands.Such a demand occurs, for example, after loading hasbeen completed.24-17. Blast chilling is also an excellent means of

auxiliary refrigeration in transit, especially after partialunloading or extended periods of parking (meal times,vehicle servicing, etc.). In addition, it can supplementmechanical cooling if the mechanical refrigerating systemshould fail.*24-18. Let us compare blast chilling with mechanical

cooling in regard to initial temperature pulldown. Thus,while some tests made by some users and reported intrade publications have shown that blast chilling withliquid CO2, started at +40° F., drops trailer temperature to-40° F. in 3 minutes, mechanical cooling required 12hours to cool the same trailer from +40° F. to -10° F.*24-19. There are two supplemental benefits when blast

chilling is used. First, the refrigerants (carbon dioxideand nitrogen) are inert gases, which will not harm mostcargoes but will in many cases benefit the cargo byblanketing it against contact with the oxygen andmoisture of the air. Secondly, the quick temperaturereduction minimizes initial thawing and cuts down oreliminates refreezing. Blast chilling cools the entire

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trailer quickly, including the "hot spots" near the doors.*24-20. The equipment for blast chilling is very simple.

It consists of CO2 tanks, a liquid control valve, flexiblehose, and a nozzle arrangement. A manifold is necessaryif a bank of tanks is used.*24-21. Safety measures. Adequate vents or openings

must be provided to relieve any buildup in pressure andfacilitate the complete displacement of warm air withcold CO2 vapor. During the first half minute or so ofblast chilling, we recommend that you leave a doorpartially open. Special clothing should be worn duringblast chilling. This may include gloves, coveralls, faceshield, etc. You must be conscious at all times that youare working with liquids at very low temperatures andsubstantially high pressures. Blast chilling fills the entirecargo space with refrigerant gas, CO2 or gaseous nitrogen,and, at the same time, decreases the oxygenconcentration to a point where the atmosphere is nolonger safe for breathing. During this operation, no onemay be present in the space. Furthermore, thecompartment must be vented before anyone enters itafter the operation is completed.*24-22. Dry ice versus liquid. The use of liquid CO2 (dry

liquid nitrogen) for blast chilling must be compared tothe more conventional use of solid CO2 (dry ice). Onepound of liquid CO2 does produce less refrigerating effect(B.t.u./lb.) than a pound of dry ice, but several factorsmake the liquid a more suitable refrigerant for blastchilling. These are: (1) the immediate vaporization ofliquid CO2 can pull the temperature down much fasterthan dry ice can; (2) the injection of liquid CO2 can becontrolled automatically and at much higher rates thanare feasible with dry ice; and (3) liquid CO2 is easilystored and is ready for use at any time. Also, (4) dry icerequires delivery shortly before it is to be used andcannot be stored (for practical purposes) for long periodsof time. Finally, (5) and (6) liquid CO2 can be handledmore easily and at a lower cost than dry ice can.24-23. Complete Liquid CO2 Truck Refrigeration.

The use of liquid CO2 for truck refrigeration has beendeveloped recently. Carriers have long desired arefrigeration system that would require less maintenanceand fewer breakdowns than is usual with mechanicalsystems. Tests have shown that a liquid CO2 system ispractical. It has only one moving part, which is thecontrol valve used to turn the system on or off. Apressure reduction valve is also necessary for safeoperation of the system. Besides the ducts and nozzles,there are the storage tanks, which present the maindrawback of the system. These tanks are very heavy,

have a charge which is limited by the size of the tank,and need special equipment for recharging.24-24. For continuous cooling, the control valve would

be operated by a thermostat. For blast chilling, the samesystem would serve by operating the control valvemanually to attain the desired cooling. The sameprecautions and safety rules for blast chilling must also beobserved with continuous cooling. Remember, wheneither liquid carbon dioxide or dry ice is used, therefrigerated area becomes dangerous to life because ofthe displacement of oxygen.

25. Automotive Air Conditioning25-1. There are various types of automotive air-

conditioning installations. Among these are the dash,trunk, dash-and-roof, and dash- and trunk-mounted units.The basic components in each of these installationsremains the same as those for the reach-in and walk-inrefrigerator. Paragraphs in this section which are markedby an asterisk (*) are reprinted in whole or in part fromthe Mark IV Service Manual by courtesy of John E.Mitchell Company, Dallas, Texas. This source is used sothat specific information can be given on the latestcomponents and procedures. Let us first consider therefrigerant and oils recommended for Mark IV units.*25-2. Refrigerant. R-12--clean, dry and free from

contamination-is the only fluid to be used in Mark IVunits. It is nontoxic, noncorrosive, nonflammable,nonexplosive and odorless under ordinary usage.CAUTION: There is one exception to the above: R-12released in the presence of an open flame will formphosgene gas, a lung irritant. Although it is a saferefrigerant, certain precautions must be observed whenhandling it or when servicing any unit in which it is used.At normal atmospheric pressure it will, in a liquid state,evaporate so quickly that anything it contacts will freeze.*25-3. Refrigerant Oil. The Yolk or Tecumseh

compressor may be used in a Mark IV unit. Either oftwo types and grades of compressor oil may be used withYork compressors: Suniso No. 5 or Texaco "Capella E."The Tecumseh model HA compressor uses a special dualinhibited oil: Suniso 3 G Dual inhibited or TexacoCapella B inhibited. These oils have been highly refinedand sealed against moisture contamination.

• DO NOT transfer to any other container for useor storage.

• DO NOT at any time, other than when pouring,allow the oil container to remain uncapped orloosely capped because moisture from thesurrounding atmosphere will be absorbed.

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It is especially important to use only recommended oils ina compressor during the warranty period. Use of otheroils will void the warranty in the event of failure.*25-4. Safety precautions. The following list of safety

precautions is intended for you, the automobile air-conditioner serviceman. Observance of these points mayavoid personal injury to you, damage to your equipmentand to your customer's car-as well as possible lostmanhours.

a. Never remove the automobile radiator pressurecap when the engine is hot.

b. Never close the compressor discharge valve withtie unit in operation.

c. Keep your hands clear of the automobile enginefan and belts when the engine is running. This shouldalso be considered when opening and closing thecompressor service valves.

d. Be sure gauge manifold hoses are in goodcondition. Never let them come in contact with theengine fan or exhaust manifold.

e. Make sure refrigerant hoses are clamped so thatthey cannot come in contact with any sharp metal orwith the exhaust pipe or manifold.

f. Always wear goggles when opening therefrigeration system. Refrigerant liquid or gas canpermanently damage the eyes. (See paragraph 25-5 forfirst aid treatment.)

g. Never apply heat from a torch to a sealedrefrigeration system. Refrigerant will expand rapidly withheat and could cause an explosion.

h. Refrigerant 12 in the presence of an open flameproduces phosgene gas. This is toxic. Never breathe it.

i. Do not use refrigerants other than R-12.j. Extreme care should be taken never to use

methyl chloride refrigerants, because a chemical reactionbetween methyl chloride and the aluminum pans of thesystem will result in the formation of product which burnspontaneously on exposure to air or decompose withviolence in the presence of moisture.

k. Be sure all engine capscrews are tight and are ofthe correct length for their particular application. Pulleyscoming off at high speed can cause costly damage to theautomobile and possible injury to the occupants.

l. Wear goggles when using a hole saw or portablejig saw. This is cheap insurance for eye protection.

m. Use extreme caution when drilling holes in theautomobile. Holes drilled into the electrical wiring orinto the gasoline tank can cause fire or explosion.

n. Do not run the automobile engine in an area notwell ventilated. Carbon monoxide displaces oxygen.

o. Keep hands away from moving evaporator fansand blower wheels. High-speed motors have enoughpower to cause painful injury.

p. Use caution when working around exposedevaporator coil fins. Painful lacerations can be inflictedby the fins.

q. Do not run the automobile engine withautomatic transmission fluid lines disconnected or costlydamage to the transmission may result.

25-5. First Aid. The skin and eyes should also beprotected from contact with R-12 liquid or vapor. SinceR-12 is readily absorbed by most oils, a small bottle ofsterile mineral oil and a small quantity of boric acidshould be located near the service stall. Should R-12contact the eyes, wash them immediately with a fewdrops of mineral oil, followed by a thorough cleansingwith a weak solution of boric acid. See a physician ifirritation continues. FOR YOUR OWN PROTECTION,WEAR GOGGLES when opening the refrigerationsystem.

25-6. Components. As you know, the parts of anauto air conditioner do the same things as the parts in arefrigerator. However, because of location andenvironment, the installation and operation of some partsare quite different in an auto.

25-7. Condenser. The condenser is mounted ahead ofthe radiator for the car's engine. For this reason theengine tends to run hot, particularly at low speeds. Thismay be compensated for by using a larger fan or onewith more blades. When air conditioning is added to acar, it may also be necessary to change the standardradiator and install a larger size to keep the engine fromoverheating. The addition of an air conditioner imposesthese three new factors on the car's operation: (1) thecondenser reduces the volume of air to the radiator andthe engine compartment, (2) the compressor requires theengine to produce more horsepower while it is engaged,and (3) the heat output from the engine is more for anygiven speed. The use of ethylene glycol in the car'sradiator will help to get rid of heat from the enginefaster. Also, the engine cooling system is pressurized toincrease cooling. The radiator cap is spring-loaded toretain a certain operating pressure, usually from 4 to 16pounds, in the system. Failure of the cap to maintaincooling system pressure will result in the engine'soverheating.

25-8. Evaporator. Most units are made for mountingunder the dash or on the firewall. However, some unitshave been mounted in the trunk or in back of the rearseat The disadvantage of the rear mounting is the longruns of tubing required to connect the unit. On theother hand, a

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mounting under the dash makes the lines much shorterbut fills the center space between the dash and the floor.In any case, copper lines are not satisfactory forautomotive work, because vibration over a long period oftime will cause copper to harden and become brittle.Consequently, refrigerant lines for an automobile air-conditioning installation are made from high-pressureneoprene hose.

25-9. Receiver, drier, and strainer. On most automobileair-conditioning systems, the receiver, drier, and strainera- combined into one compact unit which is installed inthe liquid line. The function of these components issimilar to those previously mentioned. A sight glass isthe means of observing refrigerant leaving the condenser.Under normal operating conditions, a fully chargedsystem will deliver a solid stream of liquid refrigerant tothe liquid line leading to the expansion device. A clearsight glass usually indicates a fully charged system, unlessthe system is completely discharged. Bubbles in the sightglass are an indication of a partially charged system.Some units also have a moisture indicator in back of thesight glass. The moisture indicator should be blue ifmoisture is not present in the system. Moisture in thesystem would cause the blue indicator to turn pink. Donot confuse this type of indicator with those which youmay find in large refrigerator systems. (For example, oneindicator is green but turns bright yellow with moisture,while others show different color combinations.)*25-10. Expansion valve. Control of the liquid

refrigerant entering the evaporator coil is done by athermostatic expansion valve. The power clement orthermobulb and connecting tube will be charged witheither a liquid or gaseous refrigerant, usually of the typeused in the air-conditioning system. The power elementis connected to the open area above the diaphragm bymeans of a small capillary tube. The lower side of thediaphragm actuates a ball check valve by means of pushrods. Thus movement of the diaphragm provide controlof the valve inlet opening. The power element clampedto the evaporator coil outlet responds to the suction astemperature. An increase of this temperature increasesthe pressure and temperature of the refrigerant in thepower element. Conversely, a decrease of suction gastemperature decreases the pressure and temperature ofthe power element refrigerant. It can be seen from thisthat increased suction gas temperature causes theexpansion valve to open, admitting more refrigerant,while a decrease in suction gas temperature causes theexpansion valve to move toward the closed position.*25-11. RoboTrol valve. The RoboTrol valve replaces the

SelecTrol valve which was used in older models of MarkIV units. The RoboTrol valve is, like the SelecTrol, a

suction line flow control valve; but, unlike the SelecTrol,its operation is entirely automatic with no provision formanual temperature control. The function of theRoboTrol is to control evaporator pressure and volumeflow to the compressor to provide the coldest possibleconsistent air temperature without allowing condensate tofreeze on the evaporator coil fins.*25-12. Refer to figure 46, which is a cross-sectional

view of the RoboTrol revealing its internal construction.Actually the valve is quite simple, operating through. abalance between a coil spring (6) and a sealed metalbellows (7) which is subjected to suction line pressure andflow pressure drop at the valve. Increased pressurecollapses the bellows against the spring, thus moving theconical valve head away from its seat. Reduced suctionline pressure allows the spring to overcome the bellowsaction, thus pushing the valve head back toward its seat.

Figure 46. RoboTrol valve.

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*25-13. Spring tension is regulated at the factory to closethe valve when suction line pressure indicates atemperature in the evaporator coil that would causefreezing of condensate on the fins. An adjusting screw(1) is provided for changing spring tension in the field ifspecific humidity conditions require a different settingfrom that made at the factory. Turning the adjustingscrew clockwise increases spring tension to provide ahigher pressure setting. This may be necessary in areasof extreme humidity where ice can form on the coilrapidly.*25-14. It should be understood that adjustment of the

RoboTrol must not be made unnecessarily. Many milesof highway driving may be required to prove aninadequate valve setting. A low setting will besatisfactory at city driving speeds where ice has littlechance of forming but will be very unsatisfactory at roadspeeds when refrigeration capacity is in surplus. A highsetting may rob the unit of efficiency at all speeds.*25-15. Correct setting of the RoboTrol will maintain

about 26 p.s.i.g. in the evaporator coil. Because the valveis connected directly to the compressor and suction-pressure readings are normally taken at the compressor,pressure drop in the suction line must be considered. Fornormal operation in all areas the valve should be set toclose at 17 p.s.i.g. and to open at 19 p.s.i.g. pressure withreadings taken upstream from the valve.*25-16. Other than adjustments described above, no

service to the valve can be carried out. A leaking valvemust be replaced. When installing a RoboTrol, use thebackup flats provided on the inlet side fitting to avoidstrain and possible distortion of the outlet connection atthe compressor. This distortion will cause icing of theevaporator regardless of the adjusting spring setting.*25-17. Thermostatic controls. Three types of thermostats

have been used in Mark IV units, beginning with theCommuter and Sportsman Evaporators in 1961. Theseunits used a bimetal type thermostat responsive todischarge air temperature. The thermostat as applied inthe 1962-63 Monitor has a control lever and pin. Whenreplacing this lever-actuated thermostat, move the controllever to the extreme right end of the slot. Position thethermostat so that the lever and pin lightly touch oneanother. Tighten the mounting screws in this position.Low temperature cut off is 28° F.*25-18. Electrical system. All wiring is stranded copper

with plastic covering. Most 12-volt units will have No.16 wire, while No. 12 wire is furnished for 6-volt units.The Sportsman unit uses No. 14 wire for either voltage.*25-19. Fuses. Prior to the 1962 Monitor, all units

provided for a fuse or fuses between the automobile

ignition switch accessory terminal and the evaporatorswitch. Fuse requirements are a 20-amp fuse for 14-voltcircuits and a 30-amp fuse for 6-volt circuits. Instead ofa conventional fuse, the 1962-65 Monitor has a 15-ampcircuit breaker, mounted at the rear of the evaporator.The circuit breaker has a current rating of 15 amps at 20percent overload for 30 minutes.*25-20. Motors. Three motor types have been used since

1958 with Mark IV units. While differing in size andnumber as well as length of shaft extension, all are serieswound D.C. Both 6- and 12-volt applications are used.No service to the motors should be required. Bearingsare porous bronze with oil saturated wicks and aredesigned to last the lifetime of the automobile withoutadditional lubrication. Occasionally a motor may chatteraudibly, especially on rough roads or when theautomobile is driven rapidly around a corner. This canusually be attributed to excessive armature end play.Correct end play, when the motor shaft is moved byhand, should be about 1/64 inch. Additional spacingwashers placed on the armature shaft inside the motorwill reduce end play. The motor housings must beseparated for installation of these washes.25-21. Magnetic clutch. A magnetic clutch has a field

coil which is stationary in one type. Another type has afield coil which rotates, and this type requires brushesand two collector rings to supply electricity to the coil.The rotating field has the possibility of trouble from poorcontact between the brushes and rings. The stationarycoil is not subject to such trouble and is thereforeconsidered to be more reliable.*25-22. Operation of the magnetic clutch is very simple.

When the current to the clutch is off, the rotor pulleyidles free on the clutch bearing. The compressor shaftdoes not rotate. When current flows to the field of theclutch, the rotor-pulley and armature (attached to thecompressor shaft) are "locked" together magnetically.The compressor shaft rotates and refrigeration isprovided. Note the following instructions for refrigerantlines which will conclude our discussion of components.*25-23. Refrigerant lines. Always use grommets where

rubber refrigerant lines pass through the radiator yoke,firewall, or trunk compartment floor. All holes forrefrigerant lines should be cut with a hole saw of theproper size, as indicated by the instruction sheet. Be surethat rubber lines are not against the exhaust manifold orany sharp metal edges and that they are clamped properlyin enough places to keep them from sagging under thecar. Clamps should be

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attached to the car with No. 10 sheet metal screws. Usea 1/8-inch drill for these screws.25-24. Control of Refrigeration. There are three

methods to control the cooling. Some units may bemore sophisticated than others, combining two of thesemethods. Here is a brief discussion of three types ofcontrol.25-25. Thermostat. A thermostat which operates a

switch is used on some units. The feeler bulb is locatedin the airstream next to the evaporator. The switchcloses the circuit to the magnetic clutch when cooling iscalled for. With this type of control the compressor willonly operate when cooling is demanded.25-26. Pressure-operated bypass. This method of control

uses a bypass valve which is operated by pressure on thelow side of the system. A diaphragm in the valvecontrols the bypass by responding to changes in pressureon the low side. As the temperature in the car becomelower, the pressure in the low side reduces, and thisreduced pressure on the diaphragm causes it to open thebypass so that refrigerant no longer flow to theevaporator. Operation of the valve is adjusted by alinkage which change spring pressure on the diaphragm.25-27. Solenoid-operated bypass. The solenoid valve is

controlled by a thermostat set in the air-stream from theevaporator. The valve opens the bypass line when thethermostat senses that the temperature in the car is coldenough. When the air becomes warm enough, thethermostat will cause the solenoid valve to close thebypass line, and the unit will again operate to cool thecar.25-28. Servicing and Adjusting. In this area we will

present service information which can be applied to mostinstallations. The owner's service manual is requiredwhen it is necessary to make exact adjustments. It is notpractical to adjust valves without the specification,because you can do more harm than good. Let us beginwith the drive pulley.*25-29. Crankshaft drive pulley. The seating and

centering surfaces, both on the air-conditioner crankshaftpulley and the original pulley hub, or balancer to which tis to be attached, must be wiped free of all dirt and gritbefore installation. Any foreign material on thesesurfaces an prevent the pulley from seating properly,resulting in a wobble which may permanently damage thepulley and balancer or cause the V-belt to failprematurely. This is especially true with respect topulleys of the type secured to the crankshaft with onlyone retaining bolt. Where a key is employed with thistype of pulley, make sure the key length is correct to justfill the key-way without causing any pulley wobble. File

or mind the key to length if necessary. To check pulleyswhich appear to be out of line, hold a straightedge againstthe faces.*25-30. Magnetic clutch removal. In most units you can

remove the clutch as follows: Remove the center boltand washer from the crankshaft. Screw a 5/8-inch NC(National Coarse) capscrew into the threads in the end ofthe clutch hub and tighten it against the crankshaft untilthe clutch comes free. Use a centering disc when youreinstall a clutch. If no centering disc is available, checkthe edge of the clutch against a fixed point on thecompressor while the clutch is slowly turned. No runoutwill be observed when the clutch is properly centered.25-31. Belts. While exact specifications are given for

some belts, you will seldom have the equipment to makeexact adjustments. The general rule calls for 1/2-inchbelt deflection between pulleys. If a belt shows rapidwear, check the pulleys for dents or scratches in thegrooves. A damaged groove will tear up a new belt. Ifthe belt shows signs of the cord separating from therubber, it indicates the belt has been stretched inattempting to force it over the pulleys. This is the maincause of ruined belts and pulleys. The fan pulley isdesigned to have at least 3/8-inch clearance between thefan and the radiator. Make a check for the cause if thereis much departure from the correct clearance.*25-32. Oil. Occasionally, after having been in service

some length of time, some units may show a grayishdiscoloration of the refrigerant and oil. This can beobserved through the sight glass which may becomecoated on the inside until it is opaque. This condition iscaused by moisture contamination and should be rectifiedimmediately. Usually, replacement of the drier issufficient, but in cases of extreme coating the expansionvalve should be removed and cleaned out manually.Then replace the valve along with a new drier. Checkthe compressor oil for severe discoloration. Drain andrefill with clean, dry refrigeration grade of oil if required.*25-33. Expansion valve. Perhaps the most important

thing to remember here is to make sure the thermobulbis good tight metal-to-metal contact with the coppersuction line. When replacing the expansion valve, sandthe bulb and suction tube mating surfaces. Then tightenthe bulb clamp securely. To avoid twisting the coppertubing, always use a backup wrench on the valve whenloosening or tightening connections.*25-34. Inadequate compressor oil, aside from causing

possible damage to the compressor, will result inimproper lubrication of the valve needle. Lack of oil atthe needle and seat materially affects the liquid seal,resulting in excessive wear.*25-35. Refrigerant lines. All hose assemblies

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are manufactured to rigid specifications. Each length ofhose is thoroughly cleaned and dried before being cut tolength for installation of couplings. When servicing, useclean refrigeration oil on all fittings-nothing else. Theuse of refrigeration oil on all fittings will aid in makingleakproof connections. DO NOT USE SEALANTCOMPOUNDS. If these compounds (blue or red incolor) are introduced into the system they will clogstrainers. The result will be complete failure or loweredefficiency and a voided warranty.*25-36. Lines must be clamped to prevent their contact

with exhaust manifolds, carburetors, linkage, etc. Be suregrommets are installed to protect hoses where they passthrough metal partitions.*25-37. Switches and rheostats. Defective switches should

be replaced. Attempted repairs are seldom satisfactory.Intermittent unit operation may be caused by a defectiverheostat. Rheostat switches with built-in clutch circuitshave, on rare occasions, been known to causeintermittent cooling. This could result from an unevenbedding of the resistor coil in the ceramic switch base.The sliding contact shoe, being moved along the resistorcoil as the switch knob is turned, may ride up on asection of the coil that is sufficiently high to lift the shoealmost clear of the clutch circuit ring. The resulting poorcontact may cause the clutch to slip or cut out. If acondition of this sort is suspected, check the clutch circuitwith a voltmeter while turning the rheostat knob slowlyback and forth. If the voltage varies sharply, replace therheostat switch.*25-38. Evacuation with a vacuum pump. The following

procedure is given for Mark IV units. However, theymay be generally applied to most auto air conditionerswhen it is necessary to remove air or moisture from asystem.

a. Remove protective caps from gauge ports ofcompressor service valves. Connect gauge manifoldhoses to appropriate compressor service valves.

b. Schrader gauge line adapters are required for all1964 compressors.

c. Connect gauge manifold center hose torefrigerant container. OPEN refrigerant container valve.(Use only refrigerant grade R-12.)

d. Crack open high-pressure gauge manifold valveand allow refrigerant vapor to enter system until apressure of 50 p.s.i.g. is observed on low-pressure gauge.CLOSE high-pressure gauge manifold valve. CLOSErefrigerant container valve and disconnect hose fromcontainer.

e. Using a leak detector, thoroughly check allconnections, the compressor, evaporator, condenser, andservice valve operating stems or Schrader fittings withprotective caps in place. Repair any leaks at this time.

f. Connect gauge manifold center hose to vacuumpump. OPEN both gauge manifold valves and startvacuum pump.

g. After vacuum pump has run at least 15 minutes,CLOSE both gauge manifold valves and stop vacuumpump. Low-pressure gauge should indicate at least 28-inch vacuum. High-pressure gauge should read zero (0)p.s.i.g. or below.

h. Disconnect gauge manifold center hose atvacuum pump and connect to refrigerant container.OPEN refrigerant container valve. Loosen gaugemanifold center hose at gauge manifold. Refrigerantreleased will purge air from hose. Tighten center hoseconnection at gauge manifold.

i. Crack open high-pressure gauge manifold valveand allow refrigerant vapor to enter system until apressure of 0 to 5 p.s.i.g. is observed on low-pressuregauge. CLOSE high-pressure gauge manifold valve.CLOSE refrigerant container valve and disconnect hosefrom container.

j. Repeat steps f. and g. This will completedouble evacuation procedure necessary for thoroughmoisture and air removal.

k. Disconnect gauge manifold center hose atvacuum pump.

l. Connect portable charging cylinder filled with R-12 to the center gauge manifold hose. Open chargingcylinder valve and purge center hose. Open both gaugemanifold hoses and admit 34 ounces of R-12 for themonitor.OR

An alternate method of charging the systeminvolves the use of cans or factory filled drums ofrefrigerant. Connect the container(s) to the center gaugemanifold hose. Purge hose and admit refrigerant untilthe system is at container pressure. Do not invert thecontainer.

m. CLOSE charging container valve and bothmanifold valves.

n. Start engine and set idle to approximately 1500rpm. If shop temperature is 90° or above, place a fan infront of radiator to simulate ram airflow.

o. With temperature control knob or lever turnedto maximum cold position, allow unit to operate for 2minutes with blower(s) on. (Monitor evaporator onlymust have a jumper wire connector from a 12-volt sourceto the clutch.) Observe the sight glass located in top ofreceiver-drier or in expansion valve body. If bubblesappear, OPEN low-pressure gauge manifold valve andcontainer valve. Add charge until bubbles disappear.

p. CLOSE low-pressure gauge manifold valve

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and turn blower(s) off. Bubbles should not a pear insight glass until low-pressure gauge reading reaches 12p.s.i.g. At low-pressure gauge reading of 8 p.s.i.g., it isnormal for bubbles to appear in sight glass. If bubbles donot appear between 12 and 8 p.s.i.g., disconnect gaugemanifold center hose from container and purge a smallamount of refrigerant from system. After purgingrefrigerant from system repeat this step until bubblesappear within a low-pressure range of 12 to 8 p.s.i.g.

q. Turn blower(s) on. When low-pressure gaugereading indicates 25 to 30 p.s.i.g., sight glass should notshow bubbles. Turn blower(s) off. Observe sight glass;bubbles should not appear at low-pressure gauge readingof 12 p.s.i.g. or above. Make at least two complete cyclesof this step. If bubbles appear above 12 p.s.i.g., addrefrigerant as described in steps o. and p.

r. Close container valve and disconnect gaugemanifold hose from contains. Remove clutch jumperwire.

s. Place a thermometer inside of discharge or coldair outlet. Turn blowers on full. Run unit 10 to 15minutes. Thermometer should read 50° dry bulb orbelow, with a return air temperature of 80° dry bulb orbelow.

t. If equipped with conventional service valves,BACKSEAT both valve operating systems and opengauge manifold valve to purge charging hoses. Ifequipped with Schrader type service valve, slowly loosencharging hoses at valve to purge. Replace all protectivecaps on compressor service valves.

*25-39. If a unit has lost its charge, follow the aboveprocedure to recharge and BE SURE TO LEAK TESTTHOROUGHLY.

REVIEW EXERCISES

The following exercises are study aids. Write youranswers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the test. Do not submit your answers for grading.

1. Why do some trucks and semitrailers requirerefrigeration? (24-1)

2. What are the two prime sources of power whichmay be used to drive a compressor for arefrigerated truck unit? (24-3, 4)

3. Which source of power (see question 2) has adisadvantage and why? (24-3, 4)

4. What is the relationship between the governedspeed of the engine and the speed at which itdrives the compressor? (24-7)

5. Explain the two methods of supplying heat tothe storage area in very cold weather. (24-8)

6. Is the gasoline-engine-operated refrigeration uniton trucks automatic? Explain. (24-9-13)

7. Explain the use of liquid for blast chilling atrailer. (24-15-20)

8. Are there dangers as well as advantages to blastchilling? Explain. (24-15-21)

9. How does the use of dry ice compare to liquidCO2 for cooling a trailer? (24-22)

10. What would be the advantages of liquid CO2refrigeration of a trailer as compared with thoseof mechanical refrigeration? (24-23)

11. Why should you use only the manufacturer’sspecified grade of refrigerant oil in a compressorfor an automotive air conditioner? (25-13)

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12. Give two conditions which require you to weargoggles when working on an auto airconditioner. (25-4)

13. How can a pressure radiator cap cause an engineto overheat? (25-7)

14. Why are copper lines unsatisfactory in anautomobile? (25-8)

15. Where would you look for a sight glass in anauto air conditioner? (25-9)

16. Compare the operation of an expansion valvewith the RoboTrol valve. (25-10-12)

17. What are the two means of protecting theelectrical system of an automobile airconditioner? (25-19)

18. What two types of fields may be used in amagnetic clutch? (25-21)

19. What should always be installed whererefrigerant lines pass through a metal wall? (25-23)

20. How could failure to clean the crankshaft orpulley hub result in wobble of the pulley? (25-29)

21. Describe how a magnetic clutch with a threadedhub can be removed without resorting to apuller. (25-30)

22. What are two causes of belt failure? (25-31)

23. The thermobulb should be checked for whatcondition if you suspect improper operation ofan expansion valve? (25-32)

24. Why must sealant compounds never be used onfittings? (25-35)

25. To insure a clean system, what is the mostimportant operation to perform when youconnect lines for charging? (25-38)

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Answers to Review Exercises

CHAPTER 1

1. A modern refrigerator is constructed of two metal shellsseparated by a layer of insulation. (1-2)

2. The insulation in a refrigerator must reduce heat transfer byconvention, conduction, and radiation. (1-3)

3. The greatest heat load is usually from the heat outside the box.(1-4)

4. Improved insulating material has resulted in molded insulationwhich is very effective and yet takes much less space than oldertypes. (1-5)

5. A moisture or vapor barrier must be used to seal the insulation.(1-6)

6. (1) New synthetic materials can be molded to fit. (2) Theyhave such a low K-factor that only half the space is needed asfor some natural products. (3) The synthetics are moreresistant to rot. (4) They have no food value to attract rodents.(1-6)

7. Breaker strips are often brittle and may be broken or kinked.Consequently, you should know the proper way to remove eachtype to prevent damage to it from forcing. Also, carelessnessmay break the wiring or heaters in the stile or mullion. (1-8,9)

8. The latch of such a refrigerator should be removed so that thedoor cannot be locked. (1-11)

9. The seal of a door gasket is checked with a sheet of thin paperfor uniform drag. (1-12)

10. The refrigerator should not be placed near an oven or heaterand should have its own branch circuit, where possible. (1-13)

11. Refrigerators for use overseas will have a special notice (usuallyposted in a conspicuous place inside the box) stating the voltageand frequency of the current for which each is designed. (1-14)

12. One thermostat senses when ice is made and starts the harvestcycle. The other thermostat senses when the storage tray is fulland holds off the harvest cycle. (1-18)

13. Automatic defrosting with an electric heater can be completedso quickly that the melted water would freeze in the drain pipeif a second heater were not used to warm the drain. (1-20)

14. Automatic defrosting with hot gas can be done with a solenoidvalve, which allows hot gas from the compressor to passdirectly through the evaporator. (1-22)

15. Electricity supplies the heat for some units made in Europe butabsorption systems in America are made for LP or natural gas.(2-1)

16. The main distinction regarding fuels is that the burner orificeused with LP gas is smaller, because LP gas has much moreheat value. (2-2)

17. The absorption cycle is based on the principle that water has astrong affinity for ammonia. (2-5)

18. Changes in heat load are reflected by a thermostat in thefreezer compartment which regulates a valve to vary the size ofthe flame. (2-5)

19. If the heater should be dislodged from the flame duringcleaning, the pushbutton would not reset the poppet. To correctthis, move the heater back into the flame, and the reset willhold. (2-5)

20. An absorption system must be kept clean. Dust and soot mustbe removed periodically from all heat exchangers, and the flamemust be properly adjusted for maximum heat and minimumcarbon. (2-6)

21. If installation is made so that the unit is not level, the systemwill not perform properly. (2-7)

22. If the fault is in the ammonia-water cycle, it may be correctedby turning the unit upside down for about an hour. (2-8)

23. Clearances in a compressor may be as little as 0.0001 inch,because it runs in a closed environment (no moisture, no acids)with a relatively narrow temperature variation. (3-3)

24. A piston may approach the head as close as possible withouttouching. Clearance may be only 0.01 inch at top dead center.(3-4)

25. Compressor valves may get noisy when their maximum lift isgreater than 0.10 inch. (3-5)

26. Rotary compressors have fewer moving parts and produce lessvibration than piston types. (3-6)

27. To do this, part of a condenser coil may be placed so as toevaporate the water collected from defrosting. (3-9)

28. A restrictor placed between two evaporator sections forces thefirst coil to operate at a higher pressure and temperature thanthe second. (3-10)

29. Because a weighted valve is sensitive to its position, anydeparture from the correct mounting angle will cause improperoperation. (3-11)

30. The critical factors in the makeup of a capillary tube are itsinternal diameter, its length, and the length of the heatexchanger portion. (3-16)

31. A bleeder resistor is connected in parallel with a capacitor tohelp absorb the discharge of the capacitor when the relaycontact open. This arrangement prevents burning of the relaycontact. (3-19)

32. A hot wire relay opens the circuit to the starting winding afterthe motor is started and provides overload protection if themotor draws too much current. (3-19)

33. A current relay is sensitive to current and is designed to releasewhen the current in the relay falls below a certain point. (3-21)

34. You would first check for an open circuit at the bleeder resistorwhen you have found relay contacts badly burned.

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35. Bubbling noise or hissing from a capillary tube is usually anindication of low refrigerant. (3-32)

36. Low voltage will cause a motor to run slow so that acompressor might have to run continuously to cool arefrigerator, resulting in high electric bills. (3-33)

37. A freezer may have frost accumulations scraped off with awooden paddle or with a stiff fiver brush. However, ice shouldnever be chipped off; it should be melted with warm water. (4-3)

38. For a freezer door to become frosted shut, the electric heaterstrip would have to be out of operation. (4-4)

39. A mistake made by many servicemen when troubleshooting isto pass over one of the more common faults because it seemstoo obvious or too easy. (5-3)

40. The advantage of placing the overload protector inside the shellis to extend the off time in case of an overload operation whichkeeps the unit from short-cycling. (5-5)

41. A thermostat closes its contacts when temperature rises, while afreezestat opens its contacts when temperature drops below itsoperating point. (5-6)

42. Checking a motor circuit with direct current is better wherethere is a capacitor, because alternating current passes through acapacitor easily and may lead to a false conclusion. (5-9)

43. When a test shows that a motor is drawing current equal to itsLRA rating, it indicates that the rotor is locked. (5-11)

44. A capacitor may be checked either (1) by charging anddischarging it or (2) by measuring the current through it. (5-12)

45. The current relay is current sensitive, and its contact first closeand then open in normal operation. (5-15, also 3-21)

46. The potential relay is voltage sensitive, and its contacts arenormally closed. The contacts should be open when the motoris running normal. (5-16, also 3-24)

47. Some of the causes of vibration in a refrigerator are loosemotor or tubing mounts, failure to remove shipping bolts, anduneven floor or refrigerator feet. (5-17, Table 2)

48. An acetylene cylinder must be secured upright because: (1) Itmust no be allowed to fall. (2) If the safety plugs blow, theywill pass harmlessly into the floor. (3) In any but an uprightposition, the material in the cylinder may become dislodged andfoul the gauges and valves. (6-2)

49. For two reasons: (1) The safety plug is at the top of thecylinder, and if it blows in an upright position the plug will beblown through the roof. (2) The tank will vent itself harmlesslyif upright, but if lying flat, it will be jet propelled. (6-2)

50. Soapy water is the correct test for an acetylene leak, since aflame could cause a flareback resulting in a cylinder fire. (6-2)

51. The reason is that even a small amount of oil or grease incontact with pure oxygen can result in spontaneous combustionor an explosion. (6-2)

52. The red hose identifies it. The acetylene valve can only beattached to the red hose because of the left-hand threads of theconnection. (6-3)

53. Regulator screws must be released before valves are opened, toavoid damaging the regulators and the gauges. (6-3)

54. The most important factor in making a leakproof solder joint intubing is to have correct clearance between the parts. (6-5)

55. You should heat the work to flow point of the alloy beforeapplying it to the joint. (6-8)

56. Valves with neoprene seats must have them removed beforeyou begin any soldering; otherwise, the heat will destroy thevalve seat, and it will leak. (6-9)

57. Flux changes its appearance with temperature. At 600° F. itmay appear puffy, and it will smooth out with a milky color at800° F., while at 1100° F. it will turn clear. (6-10)

58. In silver brazing, the copper is not heated to as high atemperature as it is in copper welding; thus the copper wouldnot tend to absorb carbon monoxide from a carburizing flame.(6-11)

59. The reason is that the oxidizing flame is used to preventformation of carbon monoxide which copper would absorb,forming a porous weld. (6-12)

60. Copper conducts heat away faster than steel; thus the weldingof copper requires a larger tip for the torch, which will give alarger flame. (6-13)

61. In stainless steel, the cut is covered with a length of weldingrod. When heated the welding rod will burn, supplying theadded heat necessary to melt out the cut. (6-15)

62. A line tap is expensive and can only be used once. Also, as thegasket hardens, it will start to leak; then the leak will have to berepaired. (7-1)

63. In a contaminated atmosphere a leak detector may be sosensitive that results continue to be erratic even afteradjustments have been made for the background. (7-3, 5)

64. If the probe is exposed to a concentration of halogens, theelectronic leak detector will be overloaded and may bedamaged. (7-5)

65. Small holes in the low side of a refrigerator or freezer can bepatched with a cold solder or glue made for refrigeration work.(7-7)

66. Before cold patching a hole, the surface must be absolutely freeof oil so that the patch will bond to the metal and make acomplete seal. Do not pack the material or force it into thetubing, where it would form an obstruction. (7-7)

67. Flux has a critical temperature. If a high-temperature flux isused with a lower temperature solder, the solder will flow easilylong before the flux. In contrast, the right flux will flow atabout the same temperature as the solder (7-8)

68. Cold solders or special glues are limited to systems chargedwith R-12 and should be used for patching only in the low side.(7-9)

69. A system can be pressurized with dry nitrogen and leak testedwith soapy water. If the system is partially charged and thenpressurized with nitrogen, a halide leak detector can be used. (7-12)

70. These are that a capillary tube should have the same length anddiameter as the one which it re-

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places. Also, the length soldered to the suction line should bethe same as that of the original heat exchanger. (7-13)

71. Gauge a wire to be sure that it is slightly smaller than the ID ofthe capillary tube. If it is the correct size, it should slip insidethe capillary easily without forcing. (7-14)

72. At any time that a system is opened, the ends should be tapedor capped to keep moisture and air out. (7-15, 17)

73. After major replacement, the system should be leak tested,evacuated, dried, charged, and checked for proper operation. (7-16)

74. The leak must be in the low part of the system at or near thecompressor, because most of the oil is stored in the compressor.(7-20)

75. If the charging line is not purged, air will be forced into thesystem when the charging valve is opened. (7-23)

76. When the suction line shows frost extending too far from theevaporator, the system is overcharged, and some refrigerantshould be bled from it. (7-24)

77. When frost extends too far on the inlet line to the evaporator(after the capillary has been replace), increase the size of theheat exchanger by soldering more capillary tube to the suctionline. (7-24)

78. The refrigerator serviceman must be able to make a leakproofjoint quickly and correctly so that moisture and air may be keptat a minimum. The shorter the time that a system is open, thebetter are your changes of purging air quickly. (7-1–24)

CHAPTER 2

1. The thermostat is set so that a thin coat of ice will form beforethe compressor is stopped. This ice provides a cushion so thatthe unit will not operate for each drink which is drawn. Thefreezestat insures that the unit will stop before ice gets thickenough to damage the tank if the thermostat fails. (8-2)

2. The waste water from a bubbler fountain is already cold, so it ismade to pre-cool the warm water before it enters the cold tank.(8-3)

3. Patching a water tank or line used for drinking purposesrequires approved materials only. Certain plastics or syntheticsare very poisonous. (8-5)

4. When different bottled beverages are cooled in the samecabinet, the thermostat would have to be set high enough forthe one kind most liable to freeze. (9-2)

5. A warm coil could lead you to a wrong conclusion if youmistake an oil cooler for a condenser coil. (9-3)

6. The big difference between ice making machines lies in theevaporator. Examples are the tray, plate, tube, channel, and celltypes. (10-1)

7. In an ice cube machine, you may find a tube type evaporator, acell type evaporator, or a plate type evaporator. (10-4–6)

8. Dissolved salts concentrate in the water that is left from icemaking. These salts would make unpalatable ice or could lowerthe freezing temperature so that the machine would not makeice properly. (10-8)

9. Aside from mechanical troubles, the water supply is the biggestsource of trouble, because it produces sediments, scale, and saltcrystals, which affect both metals and nonmetals adversely.(10-12)

10. Where multiple evaporators are used, a heat exchanger isnecessary to insure that the line will deliver liquid refrigerant toall of the expansion valves. (11-1)

11. A dry type heat exchanger must be correctly sized so that it cancool the liquids sufficiently without producing too muchpressure drop in the low side. (11-2)

12. The water pump supplies a high-velocity jet of cold water sothat it will absorb CO2. Water pressure must exceed the CO2

pressure which charges the tank to 80 pounds. (11-3)

13. If the ground connection is broken at the isolating transformer,the water pump motor would run continuously until stopped byoperation of an overload device. (11-4)

14. A simple test is to connect a jumper wire from the tank to theground side of the isolating transformer. When the groundcircuit is completed, the motor should stop if the tank is full.(11-4)

15. The use of aromatic woods, which will spoil the flavor of foods,could do this. This spruce and maple are used inside a cabinet,since they are hard and do not have an obnoxious odor. (12-2)

16. On such models, not only must the system be shut down butalso, where forced air is used, the fan must be turned off toprevent the blowing of water all over the cabinet. (12-3)

17. A "double duty" display cabinet is one in which the lowercompartments under the display section are also refrigerated.(12-5)

18. The area around the door of a display case may be warmedwith a heater strip to prevent the formation of frost. (12-6)

19. The flow of cold air must be continuous across the displaysection of an open case because it must have a curtain of coldair in order to operate properly. (12-7)

20. Storage cabinet defrosting methods are (1) compressor off-time,(2) hot gas, (3) hot wire, (4) hot water, and (5) secondarysolution. (12-8)

21. Compressor off-time defrosting is limited to cabinets operatingabove 28° F. (12-9)

22. Reverse cycle defrosting is a hot gas method, using a four-wayvalve so that the evaporator becomes the condenser and thecondenser becomes the evaporator. (12-11)

23. A high-temperature control is a safety device to terminate thedefrost cycle before the cabinet temperature rises too high. (12-15)

24. The capillary tube from a defrost valve supplies pressure tooperate a high-pressure safety control to limit pressure in thesystem. (12-16)

25. The service valves provide connection points for gauges andcharging and permit isolating the compressor from the system.(13-4)

26. The shell-and-tube condenser uses the shell to serve

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as both condenser and receiver. The tube-within-a-tube typecirculates refrigerant through the outer tube to take advantageof air cooling also. (13-7)

27. This is done because the receiver must be able to hold all ofthe refrigerant charge when the system is pumped down. (13-8)

28. The receiver outlet valve, sometimes called a king valve, isprovided with a quill, or inlet tube, which reaches to the bottomof the receiver to insure the picking up of liquid rather than gas.(13-8)

29. Reversing the flow of a drier-strainer might allow particles ofthe drier to get into the system. (13-9)

30. A good expansion valve should have modulating action, itshould not starve the evaporator, and it should not causeflooding. (13-11)

31. The automatic expansion valve works well with a water coolerbecause the load is uniform in a narrow temperature range andbecause the valve is not required to modulate. (13-12)

32. The equalizer line is used to compensate for pressure dropacross the valve. (13-12)

33. You can identify a thermostatic expansion valve by: (1) the sizeof the connections, (2) the length of the capillary, (3) the typeof charge, (4) the internal or external equalizer, and (5) thecapacity in tons. (13-13)

34. Three types of charge used in a thermostatic expansion valveare the liquid, the gas, and the cross charge. (13-13)

35. The cross charge is a refrigerant different from that used in thesystem so that the cross charge temperature-pressure curve willcross the curve of the refrigerant used in the system. (13-13)

36. The liquid-charged bulb will always have some liquid left in thebulb; thus it will continue to hold control even when the valveis colder than the bulb. Its drawbacks are the possibility offlooding and/or of hunting. (13-13)

37. The gas charge is smaller than the liquid charge; therefore themaximum operating pressure of the valve can be determined byfixing the amount of the charge. Its disadvantage is thatcontrol is lost if the diaphragm is colder than the bulb, sincegas will condense away from the bulb. (13-13)

38. The advantages of a high-side float valve are that the capacityof the valve is not subject to change from flashing and all ofthe refrigerant enters the evaporator as a liquid, so there is nolost cooling. (13-14)

39. A layer of oil on top of the refrigerant may cause the refrigerantto refuse to boil unless it is agitated or unless an ebullient isused. (13-15)

40. Before making tests on a "line" circuit, you should remove ringsand metal watchbands, because safety records show many severburns from metal jewelry which has caused a short circuit. (14-2)

41. When a circuit breaker is reset, you should determine whatcaused the trip to operate, as you can often find and correct aminor defect before it becomes a major problem. (14-4)

42. A compressor motor which draws full LRA may be good if itstarts normally with belt tension released. The indication isthat there is a locked compressor. (14-5, 6 also 5-11)

43. Trying repeatedly to start a motor with a locked rotor can causemore damage because of excessive current in the circuit. (14-6,8)

44. Causes of abnormally high head pressures are restrictionscaused by pinch, air, a clogged screen, a frozen expansionvalve, a partly closed valve, or a think head gasket. (14-9)

45. When a compressor continuously runs but does not cool, checkfor high suction pressure, which would indicate a low-siderestriction; or check for bubbles in the sightglass, which wouldindicate a low charge. (14-10, 11)

46. If the capillary in a thermostat had lost its charge, the bellowscould not expand. Since warming of the charge expands thebellows to make the compressor run, the unit would remainidle. (14-11)

47. A quick check for ice blocking a refrigerant control is to warmthe control and watch to see whether or not the pressure gaugesreturn to normal readings. (14-12)

48. When a valve is supposed to be shut and it continues to leakrefrigerant, it indicates that the needle and seat are worn. (14-13)

49. When you make adjustments or repairs on a float valve, be sureto restore its operating point to the original level of the fluid.(14-14)

50. Equipment which can be isolated from the system by valvesmust have been purged by bleeding off pressure before it isremoved from the system. (15-2)

51. The ratchet stop in a micrometer makes it possible to exert thecorrect driving force on the spindle when a measurement ismade. (15-5)

52. In figure 18, the top illustration will read 0.012 inch less if thethimble is moved 12 divisions in the direction of the arrow.Thus, the reading would be 0.292 inch. (16-5)

53. You can check the proper mating of an extension rod with aninside micrometer by measuring it with an outside micrometer.(16-5)

54. The best tool for checking a crankshaft to see whether or not itis true is a dial micrometer. (16-5)

55. Loss of oil pressure may be from (1) a low oil supply, (2) wornbearings, (3) a defective oil pump, (4) a defective oil pressureregulator, or (5) oil diluted with refrigerant. (16-6, 18)

56. When installing a new oil seal, be sure to clean all grease andpreservative from the seal, apply refrigerant oil to the seal, andcarefully inspect all seal surfaces for scratches which wouldcause a leak. (16-8–10)

57. To check a new seal for a leak, operate the compressor with thesuction line closed till the vacuum gauge levels off. Then closethe compressor discharge line and watch the high-pressuregauge for a rapid rise, which would indicated that air is beingdrawn into the compressor. (16-11)

58. Check the depth of the valve seat for too much wear, andcheck the valve to see that it is not worn too thin. (16-12)

59. Check for a slight burr or feather edge on one side of a springsteel valve. The burr could damage the sea; therefore the valveis installed with the

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burr side up. A heavy burr should be removed, as it couldproduce metal particles in the system. (16-13)

60. In a refrigeration compressor, the compressor ring usually has ataper which slopes to the top of the ring (marked “TOP”). Thetop side must be installed facing the head. Oil rings which donot have a taper may be installed with either side up. (16-15)

61. Two indications of upside-down compression rings would below oil in the sight glass and noisy compressor operation –knocking- because of pumping oil. (16-15)

62. Ring gap can be checked with a feeler gauge after the ring hasbeen inserted into the cylinder about 3/8 inch below the top.(16-15)

63. When a new set of rings is installed in an old cylinder, theglaze must be broken from the cylinder wall so that the ringswill wear in quickly. (16-15)

64. When a compressor has worn to the point of requiring newbearing inserts, other moving parts must also be inspected forsigns of wear beyond specified limits. (16-16)

65. System cleaning is required on a new installation before it isplaced in service as well as on a system which has suffered ahermetic motor burnout. (16-19)

66. While cleaning a system after a hermetic motor burnout, avoidcontact with the sludge, as it may contain acid. Also avoidbleeding contaminated refrigerant into the air, as the acid maybe strong enough to burn your eyes. (17-2,7)

67. system cleaning is done by evacuating from the high side. Thereason for doing this is to reverse-flush the system. (17-3)

68. After a system is cleaned, the drier will have absorbedconsiderable moisture, and the installation of a new drier willinsure a dry system. (17-3)

69. When cleaning a system use refrigerant to break the vacuum inorder to keep air and moisture from enter the system. (17-4, 7)

70. Activated alumina may be used as a drier only on the suctionside of a system charged with SO2 (18-5)

71. Anhydrous calcium sulfate must not be used as a drier in asystem charged with SO2. (18-7)

72. Before installing a drier, it should be opened and baked at 300ºF. for 24 hours to insure dryness. (18-9)

73. A vacuum of about 1-inch mercury is required to boil water at80º F. (18-11)

74. A vacuum pump requires that the oil be changed to get rid ofthe moisture which accumulates in the oil during service. (18-15)

Chapter 3

1. The coldest rooms are located in the center of a refrigeratedwarehouse surrounded by warmer areas which act as a bufferand make it easier to maintain zero temperatures in freezerrooms. (19-2)

2. During normal work, the floors in meat processing an storagerooms become very slipper. Also, where large quantities ofpotatoes are stored, you must have positive ventilation, as

accumulations of CO2 can cause asphyxiation. (19-4, 5, 8)

3. If potatoes in storage are piled too high – more than 6 feet –heat will accumulate in the center of the pile, and they willspoil rapidly. (19-8)

4. Using modern methods of construction provides a cold storageroom with a continuous vapor barrier to keep out moisture;also, a room which can move independent of the building. (19-10)

5. In the construction of a modern refrigerated warehouse, thevapor barrier must be attached only to the cold room walls,because they can move. (19-14, 15)

6. A blueprint can be studied to learn the meaning of symbols andgive one a mental picture of the layout of equipment. Forexample, a blueprint will show changes and additions to theplant. Also, a blueprint will often help you find the location ofequipment. Finally , you should use a blueprint to recordmodifications to the plant as they are made. (19-21, 22)

7. Blueprint details are enlargements of small parts of a drawing toshow fine points which would be lost in a small-scale diagram.(19-21, 22)

8. When four or more compressors are installed, the plant can besplit into two systems, with two compressors for hightemperature and two for low temperature. Either system cancontinue operation at reduced capacity, even if one compressorfails. (19-24).

9. The determining factor for setting the operating points of apressure control in the suction side is temperature. Adjustmentis made so that the control cuts in when the evaporator coil isat its desired operating temperature and cuts out when coiltemperature has dropped 10º F. While it is essentially a pressurecontrol, its adjustment is most satisfactory when madeaccording to temperature. (19-24)

10. True. Evaporator coil temperature is more reliable because ourconcern is to keep a room within temperature limits. Suctionpressure is more susceptible to variations which occur duringthe operation of the system. (19-24)

11. In cold weather when compressor discharge pressure drops, youcan build up pressure in the system by (1) throttling the kingvalve and (2) reducing the capacity of the condenser. (19-24,25)

12. In checking for voltage at a three-phase magnetic switch, checkthe upper terminals from A to B, B to C, and A to C. (19-24)

13. Dashpot oil is used in time-delay relays. Use of other oils in adashpot would result in erratic operation with changes intemperature. (19-24)

14. On the installation or replacement of a motor, you should test itfor correct rotation and line up the pulleys. (19-24)

15. When working on or around V-belts, you should plan onreplacing them soon, as oil causes the belt material to rot. (19-24)

16. If oil cannot be cleaned off a set of V-belts, you should plan onreplacing them soon, as oil causes the belt material to rot. (19-24)

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17. When one belt shows a flutter more pronounced than that ofthe other belts in a set, the condition indicates that the one belthas stretched in service, and the belt tension should bereadjusted before the vibration gets too severe. (19-24)

18. A gradual drop in head pressure over a few hours wouldaccompany a drop in ambient temperature. Over a few days, acontinual drop would indicate trouble. To contrast, a suddendrop in pressure usually indicates trouble. (19-24)

19. The purpose of a recording chart is to provide a continuousrecord of plant operating conditions. (19-24)

20. The purpose of bleed-of water is to get rid of some of the waterin which salts are concentrating. (19-25)

21. When makeup water is controlled automatically by a float valve,the rate of bleed-off water will determine the amount ofmakeup water added. (19-25)

22. In cold weather operation, the best method of capacity controlof an evaporative condenser is by means of modulating dampersin the air inlet. (19-25)

23. The disadvantages in operating a cooling tower are (1) scaleformation, (2) algae growth, and (3) that it must be protectedfrom freezing in cold weather. (19-25)

24. When making a walk-through inspection of a freezer room,make these checks: (I) Look for unusual sins of frost onexpansion valves and extension of frost on the lines. (2) Checkto see that fans are operating. (3) Note any unusual noise,vibration, or odor. (19-27-29)

25. A hot gas defrost system may be operated to drive out oilwhich has accumulated in an evaporator by operating thedefrost for a longer period. (19-30)

26. In an ice plant, an agitator is used to keep the brine moving toinsure transfer of heat from the ice cans to the evaporator coil.(20-3)

27. Water jackets are used to cool the head of an ammoniacompressor because of the high operating temperature ofaround 250° F. (20-3, 17)

28. Three factors in making a good grade of ice are (1) a brine at15° F., (2) agitation of the ice water during freezing, and (3)removal of the core water and replacing it with fresh water atthe proper time. (20-5)

29. A core sucker is necessary to remove the core water thatcontains a large concentration of salts which, if left, would takemuch longer to freeze and would make ice with a disagreeabletaste and odor. (20-5, 10)

30. While the brine temperature is 15° F., it must circulate aroundthe evaporator coils which are at 5° F.; consequently, thesolution is adjusted low enough to keep it from forming icearound the evaporator. (20-15, 16)

31. Inhibited acid should be prepared in a crock or wooden barrel.Goggles, rubber gloves, and apron must be worn. Inhibitorpowder is first dissolved in water at the rate of 3 2/3 ounces ofpowder for each 10 gallons of water. Muriatic acid is addedslowly at the rate of 11 quarts of acid to each 10 gallons ofwater. Use commercial grade acid of 1.190 specific gravity.(20-19)

32. Baking soda should be at hand for instant use to neutralize anacid burn of the skin. It can also be used to check the strengthof the acid solution during the cleaning process. (20-19, 20)

CHAPTER 4

1. Capacity control for a variable heat load is obtained by usingmultiple compressors. (21-1)

2. Two applications are multiple evaporators operated at the sametemperature and multiple evaporators at different temperatures.(21-2)

3. Types of evaporator-regulating valves are: (1) bellows, (2)diaphragm, (3) two-temperature, (4) snap-action, and (5)thermostatic. (21-4-9)

4. With multiple evaporators at different temperatures, checkvalves are installed in the suction line of each of the colderevaporators. (21-10)

5. The coldest evaporator must make up more than half of theheat load or it will not pull down to the desired temperature.(21-11)

6. Since the coldest evaporator has the lowest suction pressure, itwill be controlled by the low-pressure cutout. (21-13)

7. When the solenoid valves are closed the evaporators arepumped down, so the receiver must be large enough to hold thetotal system charge. (21-15)

8. A solenoid valve in the suction line may allow liquid refrigerantto accumulate and flood into the compressor, causing damagewhen the valve opens. (21-16)

9. The main difficulty with compressors in parallel is insuringequal division of the oil. (22-1)

10. For good operation in parallel, compressors should be the samemake and size and all interconnecting lines should be balanced.(22-2)

11. Oil equalizer and gas-equalizer lines must be connected betweencrankcases of multiple compressors to insure lubrication. (22-4)

12. With multiple compressors, a time delay allows a 10- or 15-second interval between the starting of the first compressor andthe second. (22-6)

13. An ultralow-temperature chamber is used to test aircraft andweapons. (23-2)

14. A test chamber which makes rapid changes to ultralowtemperatures must have an insulation such as Ferrotherm,which has a low heat capacity. (23-3)

15. Two methods of staging are compound compression andcompressors in cascade. (23-5)

16. A direct compound system has two compressors in series withan intercooler between, for better efficiency. (23-6, 7)

17. Since there are two separate systems in a cascade system, tworefrigerant having different temperature ranges may be used.(23-9)

18. Three refrigerants for ultralow temperatures are R-12, R-13, andR-22. (23-11)

100

19. At ultralow temperatures, an ordinary expansion valve requiresexcessive superheating at the bulb location to operate the valve.(23-12)

20. Ultralow temperature requires a special cutout because aconventional model is not satisfactory for a vacuum over 20inches Hg. (23-14)

21. To avoid problems from wax in an ultralow-temperaturesystem, a high grade oil and oil separator are used. (23-15)

22. Warm the frozen valve carefully and if it is released at atemperature colder than 32° F., the difficulty is the result ofwax formation. (23-16)

CHAPTER 5

1. Trucks which must transport perishable foods re- quirerefrigeration to prevent spoilage. (24-1)

2. The primary source of power may be either a small gasolineengine or the main engine which powers the truck. (24-3, 4)

3. Using the main engine as the primary power source is lessadvantageous, since the compressor stops when the truck engineis stopped. (24-3, 4)

4. When engine speed is governed for 2400 r.p.m., the compressoris driven at 1800 r.p.m. (24-7)

5. Heat may be furnished by a blower and an electric heating coil,or it may be supplied from operating the unit, with the defrostvalve open so that hot gas flows through the evaporator. (24-8)

6. Yes. All of the controls operate automatically, except thestarter switch, the heat-cool switch, and the defrost switch. (24-9-13)

7. Liquid CO2 is released into a trailer as a fog, which removescargo heat very quickly. (24-15-20)

8. Yes. While blast chilling can cool a trailer in a few minutes,the atmosphere will have too little oxygen for breathing, andprotective clothing should be worn to protect against frostburns. (24-15-21)

9. The liquid CO2 vaporizes faster than dry ice, so it will cool agiven area in less time than the water. Also, the liquid can becontrolled easily by a valve. Finally, the liquid is stored in tanksfor use at any time, while it is impractical to store dry ice for anextended period of time. (24-22)

10. The liquid CO2 refrigeration of a trailer is more reliable becauseit has a minimum of moving parts and reduces temperaturefaster. (24-23)

11. The manufacturer's warranty may be void if a compressor failswhile operating with an unrecommendable oil. (25-3)

12. You should wear goggles when opening the refrigeration systemand when using a hole saw or portable jig saw. (25-4)

13. Failure of the radiator cap to maintain pressure can cause anengine to overheat. (25-7)

14. Vibration causes copper to harden and become brittle. (25-8)

15. You would look for a sight glass in the receiver-drier-strainer,located in the liquid line. (25-9)

16. An expansion valve operates by means of a thermo-bulb tocontrol liquid refrigerant to the evaporator. A RoboTrol valveoperates by means of suction line pressure to control evaporatorpressure and volume flow to the compressor. (25-l0-12)

17. Either fuses or a circuit breaker may protect the electricalsystem. (25-19)

18. A magnetic clutch may use a stationary field coil or a rotatingfield coil with brushes and collector ring. (25-21)

19. Always install grommets on a line where it passes through ametal wall. (25-23)

20. Failure to clean dirt from the shaft or hub may prevent propermating causing a pulley to wobble. (25-29)

21. A magnetic clutch can be removed without a puller if its hub isthreaded. Screw a 3/8-inch NC capscrew into the bulb andtighten it against the crankshaft until the clutch comes free. (25-30)

22. Two causes of belt failure are damaged pulley grooves andseparation of belt material because of being stretched too tight.(25-31)

23. When you suspect improper operation of an expansion valve,check the thermobulb to see that it is securely clamped andmakes metal-to-metal contact with the suction line. (25-32)

24. Never use sealant compounds on fittings as the sealant mayclog the strainer and void the warranty on the unit. (25-35)

25. When connecting lines to charge a system, always purge thelines with refrigerant before you tighten the fittings. (25-38)

101

SUBCOURSE EDITIONOD 1749 A

REFRIGERATION ANDAIR CONDITIONING III(AIR CONDITIONING)

REFRIGERATION AND AIR CONDITIONING III(Air Conditioning)

Subcourse OD 1749 Edition A

United States Army Combined Arms Support CommandFort Lee, VA 23801-1809

18 Credit Hours

INTRODUCTION

This subcourse is the third of four subcourses devoted to basic instruction in refrigeration and air conditioning.

This subcourse discusses airflow properties and temperature response including an explanation of air and temperaturemeasuring devices. Instruction is also provided on the installation, operation, and maintenance of self-contained air-conditioning units. In addition, the subcourse covers the electric motor, pneumatic controls of refrigeration, the installationof ventilation systems, and the types and components of heat pumps.

There are four lessons.

1. Temperature, Airflows, and Measuring Devices.

2. Self-Contained Units and Duct Systems.

3. Controls.

4. Evaporation, Ventilation Systems, and Operation of Heat Pumps.

Unless otherwise stated, whenever the masculine gender is used, both men and women are included.

PREFACE

THIS subcourse deals with another phase of your specialty description-air conditioning. Since the principles ofrefrigeration and air conditioning are similar, your mastery of the subject will come easy. You will find that we discussseveral components peculiar to air-conditioning systems.

To qualify you in the area of air conditioning we discuss the following systems in this subcourse:

1. Self-contained package air conditioners

2. Mechanical ventilating systems

3. Fresh sir and air duct systems

4. Control systems

5. Evaporative cooling systems

6. Heat pump systems

We're also going to refresh your knowledge of the following:

1. Components of sir

2. Temperatures, airflows, and their measuring devices

3. Design and installation factors

*** IMPORTANT NOTICE ***

THE PASSING SCORE FOR ALL ACCP MATERIAL IS NOW 70%.

PLEASE DISREGARD ALL REFERENCES TO THE 75% REQUIREMENT.

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ACKNOWLEDGMENT

Grateful acknowledgment is made to the American Society of Heating, Refrigeration ad Air-Conditioning Engineers;Johnson Service Company; Honeywell, Inc.; and Taylor Instrument Companies for permission to use illustrations and textmaterial from their publications.

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CONTENTS

Page

Preface----------------------------------------------------------------------------------------------------------------------------- i

Acknowledgment------------------------------------------------------------------------------------------------------------------ ii

Chapter

1 Undesirable Properties of Air ------------------------------------------------------------------------------------------------- 1

2 Temperatures, Airflows, and Their Measuring Devices------------------------------------------------------------------- 11

3 Design and Installation Factors----------------------------------------------------------------------------------------------- 18

4 Self-Contained Package Air-Conditioning Units---------------------------------------------------------------------------- 25

5 Fresh Air and Air Duct Systems---------------------------------------------------------------------------------------------- 43

6 Controls--------------------------------------------------------------------------------------------------------------------------- 53

7 Evaporative Cooling------------------------------------------------------------------------------------------------------------- 91

8 Mechanical Ventilation--------------------------------------------------------------------------------------------------------- 104

9 Beat Pumps----------------------------------------------------------------------------------------------------------------------- 118

Answers to Review Exercises----------------------------------------------------------------------------------------------------- 133

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CHAPTER 1

Undesirable Properties of AirHOW DOES THE atmosphere of a hospital operatingroom differ from the atmosphere of your work area?Well, the atmosphere of the operating room must be freeof foreign matter, humidity controlled, and air-conditioned. But most work areas are not air-conditionedat all. Some may have fans to ventilate the area. Sinceyour duties will bring you to areas in which theatmosphere is conditioned, you must know how tocontrol the various undesirables you might find in the air.

2. The elements you will study in this chapter areforeign material, odors, and moisture.

1. Foreign Material1. Normal air contains varying amounts of foreign

materials commonly referred to as permanentatmospheric impurities. These materials can arise fromsuch natural processes as erosion, wind, and sea waterevaporation. Such contaminants will vary considerably inconcentration but will range far below those caused bymanmade activities.

2. Some manmade contaminants are: smoke causedby transportation and industry, chemical sanitizers, andvarious dusts and sprays used in agriculture.

3. Dusts. Dusts are solid particles projected intothe air by wind, grinding, drilling, shoveling, screening,and sweeping. Generally, particles are not called dustunless they are smaller than approximately 100 microns.Dust may be of mineral type. such as rock, metal, orsand; vegetable, such as grain, flour, wood, cotton, orpollen; or animal, including wool, hair, silk, feathers, andleather.

4. Fumes. Fumes are solid particles commonlyformed by the condensation of vapors from normallysolid materials. Fumes may be formed by sublimation,distillation, galvanization, or by chemical reactionwhenever such processes create airborne particlespredominantly smaller than 1 micron. Fumes which arepermitted to age tend to flocculate into clusters of largersize. This characteristic is often made use of when wewant to remove fumes from the air.

5. Smokes. Smokes are extremely small solidparticles produced in incomplete combustion of organicsubstances such as tobacco, wood, coal, oil, and othercarbonaceous materials. Smoke particles varyconsiderably in size, the smallest being much less than 1micron and often in the size range of .l to .3 micron.

6. Air Filters. Air filters are ordinarily used toremove particles such as those found in outdoor air.Filters are employed in ventilating, air-conditioning, andheating systems where the dust content seldom exceeds 4grains per 1000 cubic feet of air. Since the purpose of afilter is to remove as much of the contamination aspractical, it is obvious that the degree of cleanlinessrequired is a major factor in determining the type of filterdesign to be used. The removal of these particlesbecomes progressively difficult as the particle sizedecreases. The installation of air filters will justify theircost through a reduction of equipment failure andhousekeeping, and by providing dust-free air for criticalmanufacturing processes.

7. Air filters can generally be classified into threegroups, depending upon their principle of operations: (1)viscous impingement, (2) dry, and (3) electronic.

8. Viscous impingement type filter. This filterconsists of relatively coarse media constructed of fiber,wire screen, woven mesh, metal stampings or plates, orsometimes a combination of these. The filter may be of(1) the unit or pane) type, which is manually cleaned; (2)the disposable type, which is replaced after it hasaccumulated its dirt load; or (3) the automatic movingcurtain type, which changes its media in the airflow whenthe pressure across the filter reaches a predeterminedpressure.

9. The viscous impingement filter derives its namefrom the fact that the medium is treated with a viscoussubstance, frequently referred to as an oil or adhesive. Inthe operation of the filter, the airstream is broken downinto small columns which are made to change directions,depending upon filter construction. At each change ofdirection, the larger dust articles continue in a straightline

1

because of their momentum, and when they impingeagainst the medium they are held by the adhesive surface.The viscous material used on this type filter requirescareful selection. In general, it is considered goodpractice to follow the manufacturer's recommendations.However, desirable characteristics of a suitable adhesiveare: (1) a low percentage volatility so as to have negligibleevaporation, (2) a viscosity that varies only slightly withnormal temperature change, (3) the ability to inhibit thegrowth of bacteria and mold spores, (4) high capillarity,or the ability to wet and retain the particles, (5) high flashand fire point, and (6) freedom from odor.

10. The arrangement of the filter medium is one oftwo types. The high velocity type has the filteringmedium placed on edge, perpendicular to the base of theduct, so as to offer low resistance to airflow. Filters inthis category carry a face velocity rating of 480 to 520f.p.m. This filter does not have any recommendeddirection of airflow.

11. The progressive pack or progressive densitydesign, in which the medium is packed more densely onthe leaving air side, permits the accumulation of dirtthroughout the depth of the media. Filters of this designare rated at a face velocity of 300 to 350 f.p.m.

12. Unit filters generally have metal frames whichare riveted or bolted together to form a filter bank orsection. The rate at which they need cleaning dependsupon the type and concentration of the dirt in the airbeing handled. Various cleaning methods can be used,but the most widely used procedure is to wash the filterwith steam or water (frequently using a detergent) andthen dip or spray the filter with its recommendedadhesive. Excessive adhesive should be allowed to drainoff before you reinstall the filter in the air-stream.

13. Manometers or draft gauges are often used tomeasure the pressure drop across the filter and therebyindicate when the filter requires servicing. Unit filters areserviced when the pressure drop reaches 0.5 inches watergauge pressure. A visual inspection should be madeperiodically if a manometer or draft gauge is not installedin the system.

14. The disposable filter is constructed ofinexpensive materials and is to be discarded after oneperiod of use. The cell side of this design is acombination of cardboard and metal stiffeners.

15. The moving-curtain viscous filters are availablein two main types. In one design the filter medium isinstalled on a traveling curtain which intermittently passesthrough an adhesive reservoir, where the medium givesup its dirt load and takes on a coating of new adhesive.The medium used in the design consists of metal panelsor sections made of screen wire, stamped plates orbaffles, or reinforced mesh, which is attached to a pair of

chains. The chains are mounted on sprockets located inthe top and bottom of the filter housing. The mediumthus forms a continuous curtain which moves up oneface and down the other.

16. Automatic filters of this design may often utilizea timer for periodical filter movement. The timer is soset that it allows the curtain to make one revolution every24-48 hours.

17. The precipitated dirt must be removed from theadhesive reservoir. This is done by scraping the dirt intoa tray which can be conveniently suspended from thereservoir lip. The frequency of dirt removal is variable,but in normal operation, this type of filter will requireattention approximately once every 3 months. Where itis desirable to eliminate this maintenance, the adhesivemay be pumped through oil clarifiers or can be allowedto circulate through large settling tanks.

18. The moving-curtain filter is also available in rollform, which is fed automatically across the filter face.The dirty medium is rewound on a spool at the bottomof the filter housing. Movement of this type filter iscontrolled by a pressure switch control.

19. Filters of this type are considered to be fail safe,as they have a trip switch that indicates that the filtermedium is exhausted. This switch also opens the circuitto the filter drive motor.

20. At this time you must remove the old filter andspool and insert a new one. The old filter is notreusable.

21. Most automatic types of viscous filters areequipped with a fractional horsepower motor operatingthe drive mechanism through a gear reducer. Theoperating period is adjustable so that the media travel canbe adjusted for changes in dust concentration. Inoperation the resistance of an automatic filter will remainconstant as long as proper operation is obtained. Aresistance of 0.4 to 0.5 inch water gauge pressure at aface velocity of 500 f.p.m. is typical of this class filter.

22. Dry type air cleaners. The media used in dry typeair filters are usually fabriclike or blanketlike materials ofvarying thicknesses. Media of cellulose fiber, bondedglass, wool felt, asbestos, and other materials are used.The medium is frequently supported by a metal frame inthe form of pockets or V-type pleats. In other designsthe media can be constructed to be self-supporting. Thepockets and pleats provide a high ratio of filter area toface area.

23. The efficiency of the dry filter is higher thanthat of the viscous impingement type. The wide choiceof filter media makes it possible to supply a filter for anycleaning efficiency desired. The life or dust holdingcapacity is lower than the viscous impingement filter,because the dust tends to clog

2

the fine pore or openings. Dry filters have a large lint-holding capacity because of the large surface area exposedby the pleated arrangement of the media.

24. Types of media which provide extremely highcleaning efficiency consist of pleated cellulose-asbestospaper, sand beds, compressed glass fibers in the form ofpaper, or glass fiber blanket material. The use of thesefilters is limited to concentrations in the range of outdoorair and where efficiencies to 99.95 percent on submicronparticles are required.

25. In some designs of dry type air filters, the filtermedium is replaceable and is held in position inpermanent metal cell sides. Other dry air filters arediscarded after one period of use.

26. The initial resistance of a dry type filter will varywith the medium being used. A number of commercialdesigns have an initial resistance of 0.1 inch water gaugepressure and are replaced when a final resistance of 0.5inch water gauge pressure is reached. The more cleaningefficiency the filter offers, the more resistance there willbe to airflow. In any event, the filter should becompatible with the resistance against which the fan willbe called upon to operate.

27. Automatic dry filters are similar to the roll typeviscous impingement filter. These filters are notrecommended for handling of atmospheric dust, but areused in such applications as textile mills, drycleaningestablishments, and printing press room operation.

28. Electronic air filters. The two types of electronicair filters are the ionizing type collectors and chargedmedia type collectors.

29. The ionizing type electronic air filter uses theelectrostatic precipitation principle to collect particulatematter.

30. In a typical case, a potential of 12,000 volts maybe used to create the ionizing zone, and some 6000 voltsbetween the plates upon which the precipitation of dustoccurs. Safety devices are used to protect personnel fromshock. The door to the filter section is outfitted with aswitch that will open the circuit to the filter plates.

31. The voltage necessary for operation of theequipment is obtained from high-voltage, direct-currentpower packs which operate from a 120-volt, 60-cycle,single-phase power supply. Power consumption isapproximately 12 to 15 watts per 1000 c.f.m. plus about40 watts required to energize the rectifier tube heaters.

32. Filters of this type have very little resistance toairflow. Therefore, care must be exercised in arrangingthe duct approaches on the entering and leaving sides ofthe filter in order to evenly distribute the air across theentire area of the filter. The efficiency of the filter issensitive to air velocity. In most systems, resistance isdeliberately added in the form of a perforated plate,

prefilters, or afterfilters for the purpose of obtaining auniform distribution of air. The resistance generallyranges from 0.15 to 0.25-inch water gauge pressure atvelocities of 300 to 400 f.p.m. Screens of 16 meshshould be installed across outdoor air inlets to preventlarger foreign objects from entering the system. Specialdevices must be installed in front of the ionizing filter toremove excessive lint.

33. The ionizing type electronic filter is veryefficient. It is available in either fixed or movingcollector types. The fixed collector plates are oftencoated with a special oil which acts as an adhesive.Cleaning is accomplished by washing the cells in placewith hot water from a hose or by means of a fixed ormoving nozzle system. The bottom of the filter chamberis made watertight and is provided with a drain.

34. In one moving-plate type the grounded elementson which the dirt collects are mounted so as to form atraveling curtain. The traveling curtain intermittentlypasses through a reservoir containing a fireproof chemicaladhesive. This unit is equipped with wipers whichremove the collected dirt from the plates. The dirt thensettles as a sludge in the bottom of the reservoir fromwhich it must be removed periodically.

35. The charged media type electronic filter consistsof a dielectric filtering medium, usually arranged in pleats,as in the typical dry type filter. The dielectric materialmay consist of glass fiber, cellulose, or other similarmaterials. The medium is supported on or is in contactwith a gridwork consisting of alternately grounded andcharged members, the latter being held at a potential of12,000 volts d.c. so that an intense and nonuniformelectrostatic field is created through the dielectricmedium. Airborne particles approaching this field arepolarized and drawn toward filaments or fibers of themedia.

36. The precipitator of this type offers resistance toairflow. The resistance, when clean, is approximately0.10-inch water gauge pressure at 250 f.p.m. velocities.The resistance of this type filter increases as dustaccumulates on the media. Like the typical replaceablemedia dry filter, the charged media precipitator isserviced by replacing the medium. The dielectricproperties of the media become impaired when therelative humidity exceeds 70 percent.

2. Odors1. Odor is defined as that property of a substance

which excites the sense of smell. To be odorous, asubstance is usually in a gaseous or vapor state, orpossesses a vapor pressure. Some odors are pleasant,others unpleasant, depending

3

upon their psychological and sociological association.2. The sources of odor that cause discomfort to

individuals are many. They may be introduced from theoutdoor atmosphere and contain a high percentage ofhydrogen sulfide, industrial effluents or smog. Inenclosed areas, odors may be caused by the human body,tobacco, etc. Odors may also be caused by wet, dirty air-conditioning coils. The metals and coatings used on coilsmaterially affect the possibility of producing objectionableodors.

3. Odor removal may be done by physical orchemical means. Ventilation with clean air, air washingor scrubbing, charcoal adsorption, and masking arephysical methods; while chemical adsorption, destructionof odor sources, vapor neutralization, and catalyticcombustion are chemical methods.

4. Washing and scrubbing, like filtering, areapplicable to the removal of particulates and, in somecases, are means of recovery of a valuable product.Odors associated with the particulates are removedindirectly by this process. Combustion is employed toalleviate the effects of harmful exhaust gases andparticulates on people, vegetation, and property.

5. Ventilation, charcoal adsorption, and maskingare effective in air-conditioning for odor control. We willlimit our discussion to these three.

6. Mechanical Ventilation. Ventilation systemssupply fresh air where natural ventilation is insufficient;remove heat, vapor, or fumes from a building; anddischarge these undesirables to the atmosphere. It hasbeen found that 30 c.f.m. per person is necessary foreffective ventilation in sports arenas to avoid eyeIrritation, odors, and impaired visibility.

7. The actual oxygen requirement per person varieswith the activity. It is normally about 0.89 cubic feet perman-hour when the activity is walking at the rate of 1mile per hour.

8. Smoke and other solid or liquid particulates canbe effectively removed by electronic precipitators orabsolute liters. Odors, gases, and vapors can be removedeffectively by charcoal adsorbers. Considerable fuel andpower savings can result from the use of charcoaladsorbers as compared to ventilation.

9. Charcoal Adsorption. Charcoal adsorption isthe physical condensation of a gas or vapor on thecharcoal sorbent. The charcoal or carbon is especiallyprepared from coconut shells, peach kernels, or othermaterials. To increase the surface area and therebyincrease the adsorption capacity, the charcoal or carbon isactivated.

10. The preparation of activated charcoal is usuallydone in two steps: first, the carbonization of the rawmaterial; second, the high temperature oxidizing process.The purpose of the oxidizing process is to remove from

the capillaries of the raw material those substances whichcannot be carbonized. This is done to create extensivesurfaces on which adsorption can take place.

11. Coconut charcoal, properly prepared, isconsidered the standard high quality material for air orgas purification in air-conditioning systems. The qualityof charcoal as an adsorber of gases is rated on thebreakthrough time when subjected to the standardAccelerated Chloropicrin Test. The capacity of charcoalto adsorb gases or vapors depends primarily on the typesof gases and vapors being adsorbed. Some are readilyadsorbed, while others are not. Improved adsorption ofvarious gases and vapors can be obtained by impregnationof the charcoal with certain mineral salts.

12. Masking. Odor masking is the process of hidingone odor by superimposing another odor to create a moreoverpowering sensation, preferably pleasant. The maskingagent, which can be in spray cans, wick bottles, etc., doesnot alter the composition of the pre-existing odors. Itsimply covers such odors during the period of its additionto, or presence in, the air.

13. The application of a pleasant masking agent toan offensive atmosphere may result in a finalcombination that is still objectionable to the sense ofsmell. Therefore the objectionable odor concentrationmust not be so intense that the masking agent is itselfrequired in objectionable quantities.

3. Air and Water Vapor1. As we have stated previously, air is made up of

various mixtures, including gases and moisture. We willdiscuss moisture in the air and its relation inpsychrometry, and the means used to add or remove itfrom the air.

2. Psychrometry. Psychrometry literally means themeasurement of cold. It is the name that has been givento the science that deals with air and water vapormixtures. The amount of water vapor in the air has agreat influence on equipment cooling and humancomfort. Such atmospheric moisture is called humidity,and the common expression "It isn't the heat, it's thehumidity" is an indication of the discomfort-producingeffects of moisture laden air in hot weather.

3. The water vapor in the air is not absorbed ordissolved by the air. The mixture is a simple physicalone, just as sand and water are when mixed. Thetemperature of the water vapor is always the same as theair.

4. When the air contains all the water it can hold,it is called saturated air. The amount of moisture presentat the saturation point varies with the temperature of theair. The higher the temperature, the more moisture theair can hold.

4

5. Moisture Removal. The moisture in the airmay be removed by various methods. We will discussthe mechanical and chemical methods.

6. Dehumidifying coils. Air can be cooled anddehumidified by passing it over the cold surfaces ofcooling coils. The efficiency of this process may have tobe checked if the desired values are changed or thesystem becomes unbalanced. In a later chapter you willbecome acquainted with methods of checking theefficiency of this type of system.

7. When dehumidification is accomplished withcooling coils, the coil temperature must be below thedewpoint temperature of the humid air. This low coiltemperature causes the moisture in the air to condenseout. The air is then reheated to lower the relativehumidity. For example, an entering air condition of 100°F. dry bulb and 67 percent relative humidity could beconditioned to 70°-72° F. dry bulb and 40-50 percentrelative humidity by the following procedure:

a. The air being drawn into the system is preheatedif it is below 70° F.

b. The air then passes over the cooling coil. (Coilsize is calculated by c.f.m., approximately 400 c.f.m. perton of refrigeration.) The air is now cooled toapproximately 33° F. and has a relative humidity of 100percent.

c. It now passes to the reheat coil, where itstemperature is increased to 65°-70° F. The relativehumidity is now 20-30 percent.

d. We can now add humidity to the air if desired.Adding humidity to the air will be discussed later in thischapter.

8. Chemical dehumidification. Sorbents are solid orliquid materials which have the property of extracting andholding other substances (usually gases or vapors) broughtin contact with them. The sorption process alwaysgenerates heat, which is the major factor indehumidification. All materials are sorbents to a greateror lesser degree. However, the term "sorbent" refers tothose materials which have a large capacity for moistureas compared to their volume and weight. We will discussthe liquid absorbents and the solid adsorbent.

9. The liquid adsorbent (sulfuric acid, lithiumchloride, lithium bromide, etc.) can adsorb moisture fromor add moisture to the air, depending upon the vaporpressure difference between the air and the solution.

10. For dehumidification, the strong adsorbentsolution is pumped from the sump of the dehumidifier tothe sprayers. The sprayers distribute the solution over thecontactor coils.

11. The solution, at the required temperature andconcentration, comes in contact with the humid airwhich is flowing over the coil surface in the samedirection as the liquid absorbent. Equipment is alsoavailable for counterflow operation.

12. Moisture is absorbed from the air by thesolution and is maintained at a constant condition byautomatic regulation of the flow of water through thecooling coils by means of a water regulating valve.

13. The heat generated in absorbing moisture fromthe air consists of the latent heat of condensation fromthe water vapor, the heat of the solution, or the heat ofmixing of the water vapor and absorbent. The heat ofmixing varies with the liquid absorbent used and theconcentration and temperature of the absorbent. Thesolution is maintained at the required temperature bycooling with refrigerated or cooling tower water, orrefrigerant flowing inside the tubes of the contractorcoils. The quantity of coolant required is a function ofthe temperature of the coolant and the total heatremoved from the air by the absorbent solution.

14. The dry-bulb temperature of the air leaving theliquid absorbent contactor at a constant flow rate is afunction of the temperature of the liquid absorbent andthe amount of contact surface between the air and thesolution. In most commercial equipment the dry-bulbtemperature of the air leaving the dehumidifier will bewithin 1° to 5° F. of the absorbent solution temperature.

15. The liquid absorbent is maintained at the properconcentration by automatically removing the water vaporscondensed from the air. Approximately 10 to 20 percentof the solution supplied by the pump passes over theregenerator coil. The coil heats the solution with steamor other heating mediums. The liquid absorbentscommonly used can be regenerated with 2 to 25 p.s.i.g.steam. The vapor pressure of the solution attemperatures corresponding to 2 p.s.i.g. steam isconsiderably higher than that of the outdoor air. The hotsolution at the relatively high vapor pressure is in contactwith outdoor air in the regenerator, where water isabsorbed from the solution by the scavenger air. The hotmoist air is discharged to the outdoors and theconcentrated solution falls to the sump. The solution isthen ready for another cycle.

16. The steamflow to the regenerator coil isregulated by a control responsive to the concentration ofthe solution circulating over the contactor coils.

17. Dehumidification by solid adsorption systemsmay be performed under static or dynamic operation.These desiccants can be silica gel, activated alumina, etc.

18. In the static method there is no forcedcirculation of air into or through the desiccant.

5

Instead, the air surrounding the adsorbent is initiallydried. Subsequently, through convection and diffusion,water vapor (humidity) passes into the air surrounding thedesiccant and then to the desiccant, where it is stored.Since considerable time is required for dehumidification,this method is used quite often in shipping and storingdelicate instruments that are sensitive to moisture.Various foods, such as potato chips, also use the staticmethod of solid adsorption dehumidification.

19. On the other hand, dynamic dehumidification isoperated with forced passage of air through a desiccantbed. The only prerequisites for a dynamic dehumidifierare a desiccant bed, a fan to force the humid air throughthe bed, and a heater to reactivate the adsorbent.

20. As the air passes through the desiccant bed itgives up a certain amount of its moisture. The rate ofmoisture pickup and the humidity condition of theleaving air are functions of a great many variables. Someof these variables will be discussed later.

21. The ratio of adsorbed moisture to entering airmoisture content is known as adsorption efficiency. Theadsorption efficiency in dynamic uses remains constantand at a relatively high level until some point within thecycle, at which time the efficiency begins to drop. Thispoint is known as the breakpoint, and the amount ofmoisture adsorbed until this point is called breakpointcapacity. It is considered ideal to have the breakpointcapacity coincide with the equilibrium capacity. In actualoperation, breakpoint capacity can be a small portion ofthe equilibrium capacity, depending on operatingconditions. High inlet temperature and humidity, smallbed depths, and high airflow rates will all tend todecrease the breakpoint capacity. Regeneration of thedesiccant bed should be accomplished at breakpointcapacity, but adsorption can still be carried on. Theadsorption is now done at a slower rate until thedesiccant is completely saturated. This saturation point iscalled completion.

22. To regenerate the desiccant bed, the heater isenergized and the airflow through the bed is usuallyreversed. The temperature of the effluent air rises rapidlyat first, and then virtually levels off for a period of time.This period of time represents the period during whichthe major portion of the heat input is being used to boiloff the adsorbed water. When the latent heat(evaporization) requirements begin to diminish, the heatinput goes into sensible heat gain to the passingairstream. This period, measured from the start ofdesorption, is called temperature rise time. Althoughadditional regeneration can be accomplished beyond thispoint, it is considered uneconomical because of theslower rate of desiccant activation. Regeneration pasttemperature rise time, until the adsorbent is in moisture

equilibrium with the airstream, is known as completedesorption or desorption to completion. The energy usedin the heater per unit weight of water desorbed for anygiven time is called economy of desorption and is usuallyexpressed in kilowatt hours per pound of water desorbed.

23. Some of the many variables that influence theresults of a dynamic dehumidification operation are asfollows:

a. Variables concerning the desiccant bed:(1) Type of desiccant.(2) Dry weight of desiccant.(3) Particle size.(4) Bulk density.(5) Shape of bed.(6) Area of bed normal to airflow.(7) Depth of bed.(8) Packing of desiccant in the bed.(9) Pressure drop through the bed.

b. Variables concerning the air to be dried:(1) Flow rate.(2) Temperature.(3) Moisture content.(4) Pressure.(5) Contact time between air and desiccant.

c. Variables concerning reactivation:(1) Reactivation temperature.(2) Rate and magnitude of heat supply.(3) Heat storage capacity of the bed.(4) Temperature gradient of the bed.(5) Amount of insulation.(6) Amount of sweep gas.

24. Solid adsorption dehumidifiers are usually of thestationary dual-bed type. One bed absorbs while theother is being reactivated. The cycle time for the dual-bed operation is normally specified by the manufacturerand is controlled by a timer. Larger units may haveadjustable time cycles that can be changed for variousoperating conditions. Still others are operated from eithermanual or automatic reading of the effluent moisturecontent.

25. Humidifiers. There are many different types ofhumidifiers available for adding moisture to a conditionedarea. The types that you will study in this section are thesteam, atomizer, impact, forced evaporation, and airwasher. Of these humidifiers, the steam type is the onlyone which puts vapor into the air. All the others consistof arrangements for exposing large surfaces of water, inthe form of small droplets or wet surfaces, to the air.The water will evaporate and humidify the air.

26. Before we continue our discussion, let us reviewthe principles of humidification. Humidity refers to theamount of moisture (water vapor) in the air Absolutehumidity is the actual weight

6

of water vapor per unit volume of air. Do not confusethe term "absolute humidity" with specific humidity. It isa common error. Specific humidity is the actual weightof water vapor per unit weight of dry air in the mixture.Specific humidity is dependent upon dewpointtemperature only and is expressed in grains of moistureper pound of dry air. The continual changes in volumewhich takes place with changes in temperature and inwater vapor content make it very difficult to base anycalculations upon the volume of the mixture. Throughall of these changes, the pound of dry air remains aknown factor and a suitable basis for our measurements.As you work with air and water vapor mixturecalculations, you will realize why this basis was chosen.

27. Relative humidity refers to the amount ofmoisture actually in the air as compared to saturated air.Relative humidity depends only upon the vapor pressureof the water vapor present in the air and the dry-bulbtemperature. The presence of air or any other gas hasnothing to do with the relative humidity of a given space.

28. Now let us get back to humidification. In orderto change water to vapor we must add 1050 B.t.u.'s toeach pound of water evaporated. The heat may comefrom the air being humidified. This procedure will causethe air to cool at the same time that its being humidified.In any humidifying process in which no external heatsource is used, the wet-bulb temperature will remainconstant throughout the process.

29. Let us consider a sample of air at 80° F. dry-bulb temperature, 17 percent relative humidity, which isto be humidified to 100 percent. Using a psychromaticchart, you will find that the wet-bulb temperature is 55 F.The air will become cooler until it has reached 55° F.dry-bulb temperature. At this point the air is completelysaturated and the relative humidity is 100 percent. Youwill also notice that the dewpoint temperature has risenfrom 31.3° to 55° F. and that the moisture content hasincreased from 25.5 to 64.7 grains of vapor per pound ofdry air. You have added 39.2 grains at 0.0056 pounds ofvapor to the air. Let us now discuss the various types ofhumidifiers that use this principle. Remember, the steamhumidifier is the only type that uses an external heatsource.

30. Steam humidifier. The simplest type of steamhumidifier contains a nozzle or a set of nozzles throughwhich live steam is allowed to escape into the air. Thismeans of humidification is seldom used because steamcarries odors that are objectionable in an air-conditioninginstallation. It is also difficult to eliminate the hissingsound produced by the escaping steam. Another fault isthat the stream humidifier often provides more heat thanis desired in the conditioned area.

31. Atomizer humidifier. The atomizer humidifier isvery effective, because water is taken from a supply tankand blown into the air in the form of a fine mist. Theatomized water vapor may be sprayed into theconditioned area or into a duct leading to the area. Itfunctions much like a can of spray deodorant or aperfume atomizer.

32. Instead of the plunger arrangement found in aperfume atomizer, compressed air passes through anarrow section of pipe at a high velocity. Thismovement of air causes the water to be lifted out of thetank and be blown into the room or area. The tank isusually connected to a water supply line and is kept fullby a float valve.

33. This humidifier adds no heat to the conditionedarea. The atomized water vapor readily evaporates by theaddition of heat taken from the air within the space.The evaporation will cause the dry-bulb temperature todecrease while the relative humidity increases. The wet-bulb temperature (total heat) will remain constant.

34. While the atomizer humidifier is efficientbecause it uses all the water supplied to it, it isobjectionable in areas where noise cannot be tolerated.The noise is caused by the high velocity air passingthrough the pipe. A drainpipe is not needed because theatomizer uses all its supplied water.

35. Impact humidifier. This type of humidifier usesan arrangement similar to an air washer. Fine jets ofwater are directed against a hard surface. The impact ofthe spray upon the surface causes the water to break upinto a finer spray. The conditioned air is brought pastthe surface to pick up by evaporation as much of thespray as possible.

36. Eliminator plates are placed downstream fromthe spray to restrict large water droplets collected in theair. The water is thus prevented from entering theconditioned area and damaging the contents.

37. Twenty to fifty percent of the water supplied toan impact humidifier is actually evaporated and carriedoff in the conditioned air. This percentage varies becauseof the speed of the water leaving the jet, the entering airtemperature and humidity, and the mixing of air andwater vapor ahead of the eliminator plates. Greater jetvelocity, higher air temperature, lower relative humidity,and better mixing of air and water will increase thepercentage of evaporation.

38. Forced-evaporation humidifier. You know thatevaporation takes place continuously from any watersurface. But, do you know which factors determine therate of evaporation? First, the rate of airflow plays animportant role. If

7

more air is brought into contact with the water in a givenlength of time, more evaporation will occur. When youheat the water you are actually increasing its vaporpressure. This heating effect will allow the water toevaporate more readily.

39. Those are the two factors-airflow and heat.Now let us apply these factors to the forced-evaporationhumidifier. The forced-evaporation humidifier is sonamed because it provides a means by which water maybe evaporated into the air more than would be normal.Most of these humidifiers consist of a large shallow panin which a steam coil is immersed. A fan blows airacross the pan at a high velocity. The water level ismaintained by a float valve.

40. This humidifier does not waste any water. It issimple, in that there are no moving parts. If no heat isapplied to the water, the water will evaporate by the heatin the air, or adiabatically. When the Water is heated,both the wet-bulb temperature and the total heat willincrease. For example, if you added 40 B.t.u.'s of heatper hour to the water, and if the air is passed over thesurface of the water at the rate of 20 pounds of dry airper hour, the total heat of the air will be increased by40/20, or 2 B.t.u.'s per pound of dry air. Thus, if the airenters the humidifier with a total heat of 250 B.t.u.'s perpound of dry air and a wet-bulb temperature of 57.8° F.,it will leave with a total heat of 27.0° B.t.u.'s per poundof dry air and a wet-bulb temperature of 60.8° F.

41. Air washer humidifier. You have studied airwashers earlier in this chapter as a method of odorremoval. Now you will learn how they are used tohumidify air.

42. The spray type air washer is a very effectivehumidifier. Two banks of sprays are directed against theairflow and one is directed with the airflow. Thisarrangement of spray banks is 100 percent efficient,because all the air passing through the air washer willleave saturated.

43. If fewer spray banks are used, the efficiency willdecrease. A general comparison of the saturationefficiency is:

Number of banks Direction Efficiency1 ...........................downstream ......... 50-70%1 ...........................upstream .............. 65-75%2 ...........................downstream ......... 85-90%2............................opposing ............... 90-95%2............................upstream .............. 92-97%

44. The efficiency of a washer is usually measuredby the drop in dry-bulb temperature relative to theentering wet-bulb depression. For example, if theentering air conditions are 95° F. dry-bulb and 75° F.wet-bulb temperature with a leaving air temperature of

76° F., the efficiency is 95 percent. The principal factorsaffecting the efficiency are air velocity, the quantity ofwater sprayed per unit volume of air, the length of thechamber, and the fineness of the spray.

45. Most standard rating tables are based on avelocity of 500 f.p.m. through the air washer. Velocitiesabove 750 or below 350 f.p.m. often result in faultyelimination of the entrained moisture. The quantity ofwater sprayed per 1000 c.f.m. of air varies between 1.5and 5 g.p.m. per bank. The fineness of the spraydepends upon nozzle design and the water pressuresupplied to the nozzle. The pressure will vary between20-40 p.s.i.g. You will find that the air resistance of anair washer is usually 0.2 to 0.5 inches of water.

46. The material most commonly used in theconstruction of air washers and the other types ofhumidifiers is galvanized sheet steel. The maintenancethat you will be required to accomplish on humidifiersconsists mostly of cleaning and painting.

47. The nozzles used on impact and air washerhumidifiers are designed to produce a dense spray. To dothis with a reasonably low water pressure, the body of thenozzle may be designed to give the water a swirlingmotion as it enters the nozzle cap. The cap is cupped togive an accelerated action to the water before it emergesinto a spray at the orifice. The capacities of severalstandard size nozzles at different pressures are:

Shank Orifice Capacity of nozzle at indicateddiameter diameter pressure (g.p.m.)

10 20 25 30 401/4 3/32 0.33 0.47 0.52 0.57 0.663/8 1/8 0.59 0.83 0.93 1.02 1.183/8 3/16 1.27 1.79 2.01 2.20 2.543/8 1/4 2.01 2.84 3.18 3.48 4.02

48. Flooding nozzles are often used to providecontinuous flushing of the eliminator plates. Thesenozzles may also be used to flush the inlet baffles whenlint-ladden air is being handled. Under this condition,they operate at 3 to 10 p.s.i.g. and are spaced to handle 3to 6 g.p.m. per foot of humidifier width.

49. Corrosion is often encountered in humidifiers.When corrosion exists you must clean the humidifier andtreat the water to prevent or retard further deteriorationof the equipment. Chemical treatment should be ameans of maintaining a pH of 7.5 to 8.5. A corrosioninhibitor may also be used, if allowable.

50. Humidifier operation. A humidistat is normallyused to control the operation of a humidifier. A lowhumidity condition is sensed by the humidistat, which inturn will start the humidifier pump, position dampers,open valves, or start fans. The maintenance, adjustment,and calibration of humidistats will be discussed later.

8

Review ExercisesNOTE: The following exercises are study aids. Write your

answers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the text. Do not submit your answers for grading.

1. What factor determines the type of filter designyou would use on a particular installation? (Sec.1, Par. 6)

2. Which filter arrangement would you use in aduct system having a velocity of 500 f.p.m.?(Sec. 1, Par. 10)

3. The pressure drop through a duct system is 2p.s.i.g. What has occurred? (Sec. 1, Par. 13)

4. Which type of filter requires the least amount ofattention? (Sec. 1, Par. 17)

5. Which type of filter would you install in acritical area such as a missile complex? Why?(Sec. 1, Par. 19)

6. How can you increase the surface area of a dryfilter? (Sec. 1, Par. 22)

7. The fan motor on an air-conditioning systemoverheats. The filter is clean and the fan is notmalfunctioning. What has caused the motor tooverheat? (Sec. 1, Par. 26)

8. How many watts will an ionizing filter consumewhen 3800 c.f.m. of air is being handled? (Sec.1. Par. 31)

9. How much would it cost to operate the filter inquestion 8 for 1 hour at 3 cents a kilowatt? (Sec.1, Par. 31 and Question 8)

10. The conditioned air passing through a chargedmedia filter is not being cleaned. The dry-bulbtemperature is 50° F. and the dewpointtemperature of the air is 50° F. What hascaused the air to remain dirty? (Sec. 1, Par. 36)

11. A complaint is submitted to your shop about anair conditioner giving off a peculiar odor. Whatcondition most likely caused the air to becomeodorous as it passed through the duct? (Sec. 2,Par. 2)

12. Air at 70' F. and 100 percent relative humidityis ____________. (Sec. 3, Par. 4)

13. How many c.f.m. can be handled effectively bya 5-ton cooling coil? (Sec. 3, Par. 7)

14. How is the quality of a liquid absorbentcontrolled? (Sec. 3, Par. 12)

15. The temperature of the air leaving thedehumidifier is 10° below the absorbenttemperature. How can you correct thiscondition? (Sec. 3, Par. 14)

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16. What is the adsorption efficiency of a dynamicdehumidifier when the adsorbed moisture is 20grains and the entering air moisture content is25 grains? (Sec. 3, Par. 21 )

17. To regenerate a filter bed, 400 watts per poundof water is used. The amount of water desorbedis 3 pounds and the cost of electricity perkilowatt is 2.5¢. What is the economy ofdesorption and the cost of desorption? (Sec. 3,Par. 22)

18. How many B.t.u.'s are required to evaporate 9pounds of water? (Sec. 3, Par. 28)

19. Adding moisture to the air with an atomizerhumidifier will ____________ the wet-bulbtemperature. (Sec. 3, Par. 28)

20. How can you control the amount of humidityadded to the air with an atomizer humidifier?(Sec. 3, Par. 32)

21. What is maximum efficiency of the impacthumidifier as compared to the atomizer type?(Sec. 3, Par. 37)

22. Why does the rate of airflow play an importantrole in evaporation? (Sec. 3, Par. 38)

23. If you added 100 B.t.u.'s of heat per hour to aforced-evaporation humidifier and air is passingthrough it at the rate of 20 pounds of dry air perhour, how much heat will be added to eachpound of dry air? (Sec. 3, Par. 40)

24. The air leaving an air washer, used forhumidification, is carrying water droplets outwith it. The air velocity through the washer is800 f.p.m. How can you correct this conditionwithout altering the washer or changing thevelocity? (Sec. 3, Par. 44)

25. The resistance of the air passing through an airwasher is 2 p.s.i.g. What has caused thepressure to rise and how can it be prevented inthe future? (Sec. 3, Pan. 45 and 48)

10

CHAPTER 2

Temperatures, Airflows, and TheirMeasuring Devices

MOST MANUFACTURERS of automobiles in the pastfew years have installed warning lights to indicate heatingof the engine, low amperage output, and low oil pressure.Many times you' have probably wished to know the ratethe battery was charging or the temperature of theengine. The trend in some automobiles is back to thegauges which will tell the owner more precisely how hisautomobile is performing.

2. Lets fit this to our situation. Can you tell howhot or cold a surface is or how much air is flowing out aceiling outlet by placing your hand on it? No, you must usome type of instrument that will indicate the truecondition of the component being checked. In air-conditioning troubleshooting, you will find that thethermometer, psychrometer, and airflow measuringdevices are valuable tools.

4. Temperature1. Temperature is defined as the heat intensity or

heat level of a substance. Temperature alone does notgive you the amount of heat in a substance. It is anindication of the degree of warmth, or how hot thesubstance is.

2. The methods and scales used to measuretemperatures have been arbitrarily chosen by scientists.The most common scale that you will use is theFahrenheit scale, but we will also discuss the centigradescale. as you may come in contact with it during anoverseas tour. The Fahrenheit scale is so fixed that itdivides the temperature difference from the meltingtemperature of ice to the boiling temperature of waterinto I80 equal divisions. It sets the melting point of iceat 32 divisions above the zero indication on the scale.Therefore, ice melts at 32° F., and water boils at 212° F.(32° F. + 180° F. = 212° F.) under an atmosphericpressure of 14.7 p.s.i.a.

3. The centigrade scale has coarser divisions thanthe Fahrenheit scale, and the melting point of ice is set at0°. The boiling point is 100 divisions above this point, or100° C.

4. It may be necessary to convert a Fahrenheitreading to a centigrade reading or vice versa. For thispurpose, formulas have been developed. The formula toconvert Fahrenheit to centigrade is:

C. = 5/9 (F. -32)Centigrade may be converted to Fahrenheit by using thisformula:

F. = 9/5C. + 32

5. Sensible Heat. Sensible heat is the heat addedto a substance that causes a temperature change.Likewise, heat may be removed from a substance; and ifthe temperature falls, the heat removed is sensible heat.

6. Specific Heat. The sensible heat required tocause a temperature change in substances varies with thekind and amount of the substance. This property iscalled the specific heat of a substance and is the amountof heat required to raise 1 pound of the substance 1° F.This value is good for computations, provided no changeof state is involved. If a change of state should occur,the specific heat of the substance changes. To determinethe amount of heat necessary to cause a temperaturechange in a substance, multiply the weight of thesubstance by its specific heat. Then multiply that answerby the temperature change (B.t.u. = specific heat Xweight X temperature change).

7. Latent Heat. Latent heat is the heat that isadded or taken from a substance, causing a change ofstate. These changes of state occur without any changesin temperature or pressure. Latent heat is commonlyreferred to as hidden heat. latent heat of fusion, latentheat of vaporization, and latent heat of condensation.

8. Total Heat. Any mixture of dry air and watervapor (atmospheric air) does contain both sensible andlatent heat. The sum of these two heats is called totalheat and is usually measured from 0° F.

9. Now that we've covered the various types ofheat, we're ready to discuss temperature, or the intensityof heat.

11

Figure 1. Thermometer.

10. Dry-Bulb Temperature. In air conditioning,the air temperature is listed more accurately as the dry-bulb temperature. This temperature is taken with thesensitive element of the thermometer in a' dry condition.Figure 1 shows a thermometer common to the air-conditioning trade. Unless otherwise specified, all airtemperatures are dry-bulb temperatures.

11. Wet-Bulb Temperature. A wet-bulbthermometer is an ordinary thermometer with a clothsleeve of wool or flannel placed around its bulb and thenwet with water. The cloth sleeve should be clean andfree from oil and thoroughly wet with clean, fresh water.The water in the cloth sleeve is evaporated by a currentof air at high velocity. The evaporation withdraws heatfrom the thermometer bulb, thus lowering thetemperature. This temperature is now measured indegrees Fahrenheit. The difference between the dry-bulband wet-bulb temperatures is called the wet-bulbdepression. If the air is saturated, evaporation cannottake place, and the wet-bulb temperature is the same asthe dry bulb. Complete saturation, however, is not usualand a wet-bulb depression is normally to be expected.

12. The wet-bulb thermometer indicates the totalheat of the air being measured. If air at several differenttimes or different places is measured and the wet-bulbtemperatures found to be the same for all. the total heatwould be the same in all, though their sensible heats andrespective latent heats might vary considerably. In anygiven sample of air, if the wet-bulb temperature does notchange, the total heat present is the same even thoughsome of the sensible heat might be converted to latentheat or vice versa.

13. Dewpoint Temperature. The dewpoint dependsupon the amount of water vapor in the air. If air at acertain temperature is not saturated that is, if it does notcontain the full quantity of water vapor it can hold atthat temperature-and the temperature of that air thenfalls, a point is finally reached at which the air issaturated for the new lower temperature, andcondensation of the moisture then begins. This point is

the dewpoint temperature of the air for the quantity ofwater vapor present.

14. Relation of Dry-Bulb, Wet-Bulb, andDewpoint Temperatures. The definite relationshipsbetween the three temperatures should be clearlyunderstood. These relationships are:

a. When the air contains some moisture but is notsaturated, the dewpoint temperature is lower than thedry-bulb temperature and the wet-bulb temperature liesbetween them.

b. As the amount of moisture in the air increases,the difference between the temperatures grows less.

c. When the air is saturated, all three temperaturesare the same.

5. Relative Humidity1. The water vapor mixed with dry air in the

atmosphere is known as humidity. The weight of watervapor, expressed in pounds or grains. occurring in eachpound of dry air is called specific humidity. The amountof moisture that 1 cubic foot of air does hold at anygiven time is its absolute humidity.

2. When a gallon bucket contains 1/2 gallon ofliquid, it is 50 percent full. If a cubic foot of air thatcould hold 4 grains of moisture holds only 2 grains, it is50 percent full, or 1/2 saturated. The ratio of theamount of moisture which the air does contain to what itcould contains is called its relative humidity. Expressedin general terms, relative humidity is defined as the actualabsolute humidity divided by the absolute humidity ofsaturated air at the temperature being considered. Thesimple equation would be:

% R. H. = actual gains per pound X (100)max. grains per poundthat could be held at thegiven temperature.

3. Psychrometers. Instruments for measuring wet-and dry-bulb temperatures are known as psychrometers.A sling psychrometer, shown in

12

Figure 2. Sling psychrometer.

figure 2, consists of two thermometers mounted side byside on a holder with provisions so that the device can bewhirled in the air. The dry-bulb thermometer is bare,and the wet-bulb is covered with a wick which should bekept wet with clean water. After whirling for a minuteor two, the wet-bulb thermometer reaches its equilibriumpoint, and both the wet- and dry-bulb thermometersshould then be quickly read. The difference between thetwo thermometer readings will depend on the relativehumidity of the air. By a series of experiments, theeffect of different relative humidities has been foundthrough a wide range of temperatures. From thesevalues, tables and charts have been constructed fromwhich, when the wet-bulb and dry-bulb temperatures areknown, both the relative humidity and the dewpointtemperature can be found.

4. In the aspiration psychrometer, a small fan isused to blow the air past the mounted wet- and dry-bulbthermometers to bring about the wet-bulb equilibrium.

5. There are several types of direct readinghygrometers. A hygrometer is a device that measures therelative humidity by use of a wet- and dry-bulbthermometer. In the hygrometer a pointer is actuatedby some material sensitive to changes in the moisturecontent of the air. The pointer moves across a dialgraduated in relative humidities. While thesehygrometers have the advantage of reading relativehumidity directly, they are not sufficiently accurate formost industrial purposes.

6. At some points in an air-conditioning system,recording psychrometers are used to provide a continuousrecord of both the temperature and relative humidity.Thus they eliminate the necessity for frequent slingpsychrometer readings. Distilled water should be usedfor wetting the wet-bulb wick. If ordinary tap water isused, the dissolved solids could clog the capillaries in thecloth and the wick could become dry, resulting in anincorrect record. The air which is circulated over thebulb should be as free as possible from dust, dirt, and lintfor the wick to retain its capillary action and give anaccurate reading. At some locations where a low relativehumidity is combined with dust-laden air and water, thewet-bulb wick may have to be changed twice daily toobtain proper accuracy. Wicks may be used over againafter they are washed.

7. It is necessary to locate the sensitive wet and drybulbs in ducts and chambers remote from the recording

instrument. Remote panels are installed in ducts wherenatural circulation is adequate.

8. Psychrometric Charts. The psychrometric chartmay be used in conjunction with psychrometers todetermine the relative humidity of any particular space.These charts consist of straight lines and curves showingrelationships between the relative humidity, dry-bulbtemperature, wet-bulb temperature, dewpoint temperature,specific humidity, effective temperature, and air velocity(generally a fixed factor for each chart).

9. While relative humidity must be givenconsideration by all persons concerned with theconditioning of air, all major determinations for itsspecific control will be up to your supervisor. Theamount of moisture in a space may have to be reduced,the dry-bulb temperature may have to be changed, or thesource of moisture may have to be controlled. Whereverit is necessary, mechanical machinery and controls areinstalled to effect a continuous automatic control of thisrelative humidity.

10. The use of the psychrometric chart involves nomore than knowing the wet-bulb thermometer readingand the dry-bulb thermometer reading. Various chartsare constructed for different altitudes and situationswhere abnormally low surface pressures are encountered.Figure 3 illustrates the use of a psychrometric chart.

11. The procedures listed in the followingparagraphs may be used to find the properties of air iftwo of the properties are known:

a. Dry-Bulb Temperature. The dry-bulbtemperature is found by following the vertical lines downto the bottom scale of figure 3. detail A.

b. Wet-Bulb Temperature. The wet-bulbtemperature is read directly at the intersection of the wet-bulb line with the 100 percent relative humidity line(saturation curve). as shown in figure 3. detail A. Thescale is marked along the 100 percent line.

c. Relative Humidity. The relative humidity is readdirectly from the curved lines marked "relative humidity,"as shown in figure 3, detail B. For points between thelines, estimate by distance.

d. Moisture Content. The moisture content orabsolute humidity is read directly from the horizontallines, as shown in figure 3, detail C. It is the weight ofwater vapor contained in a quantity

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Figure 3. Segment o! psychrometric chart.

of air and water vapor mixture which will weigh 1 poundif all water vapor were extracted.

e. Dewpoint Temperature. The dewpointtemperature is read at the intersection of a horizontal lineof a given moisture content with the 100 percent relativehumidity line, as shown in figure 3, detail C.

f. Total Heat. The total heat is read directly byfollowing the wet-bulb line to the scale marked "TotalHeat," as shown in figure 3, detail A. Total heat refersto a quantity of air and water vapor mixture which wouldweigh 1 pound if all water vapor were extracted,including the heat of the water vapor.

g. Specific Volume. The specific volume is readdirectly from the lines marked "cubic foot per pound ofdry air," as shown in figure 3, detail D. For pointsbetween the lines, estimate by distance. Specific volumeis the volume occupied by a quantity of air and watervapor mixture which would weigh 1 pound if all watervapor were extracted.

h. Vapor Pressure. The vapor pressurecorresponding to a given moisture content is read directlyfrom the left-hand scale marked "pressure of watervapor," as shown in figure 3, detail C.

12. Assume that readings in an area taken with asling psychrometer were 85° F. dry bulb and 70° F. wetbulb. Use foldout at end of this memorandum andfollow along with this example. The dry-bulbtemperature (85) is located at the bottom of the chart.Following the 85 line upward until it intersects the 70.5°F. wet-bulb line (slanting downward from left to right),the user marks this point. In this example, there is nowet-bulb line for 70.5° F., so it is necessary to mark thepoint of intersection. It will be found that under theseconditions the relative humidity is 50 percent as shownby the curved line also running through this pointProjecting the point horizontally to the left of the wet-bulb scale will give a dewpoint of 64.4° F. The steepdiagonal line running through the point of intersectionindicates that a pound of air under these condition willoccupy 14 cubic feet. Projecting the point horizontally tothe right shows that there are 90 grains of water perpound of dry air. The total heat, found by following thewet-bulb line upward to the left, is 34 B.t.u.'s per poundof air, which is the heat represented by the dry air plusthe latent heat present at this degree of partial saturation(50 percent relative humidity). If the sensibletemperature were 85° F. and the relative humidity were70 percent the total heat would be 39.5 B.t.u.'s per poundof air.

6. Airflow1. Most air-conditioning systems are designed to

specifications, but you will find changes made andaccepted that will be entered on as-built blue prints. Thespecific volumes of air in each individual section shouldbe checked with the specifications or as-built drawings.

2. Air passages provide the means for air to

14

Figure 4. U-type manometer.

flow. With constantly changing requirements, a systemdesigned for a specific need may have an entire new heatload or distribution requirement. Many of us have facedthis situation, so you must understand how to makeadaptations to correct the balance.

3. Air passages for air-conditioning systems in aninstallation contain the following: air intake, return,mixing, recirculating, exterior and exit division ducts,heating, cooling, humidification, dehumidification, airwashing, filtering equipment, and inlet and discharge ofthe fan. The air passages from air-conditioningequipment to the spaces served are called duct systems.The distribution duct system includes the chamber,branches, risers, inlets, dampers, registers, returns,recirculating, mixing, baffling, and exit systems.

4. The factors that can affect air volume are thenumber of occupants, various heat transfers in buildingequipment. and temperature differences of interior andexterior spaces. All these factors are considered byengineers in their design of an air-conditioning system.

5. If the air weight or volume is determined andthe load requirements are known, then duct anddistribution systems are calculated according to velocities,pressures, and pressure drop in the duct system.

6. We will now discuss the devices used inmeasuring airflow and static and total pressures.

7. Manometers. Two types of gauges that can beused to measure air pressure are shown in figures 4 and5.

8. The pressure required for the velocity of airflownecessary to overcome all the losses

Figure 5. Slant type manometer.

throughout the duct system is called the dynamic or totalpressure. The pressure required to overcome losses dueto friction of duct systems is called static pressure.Figure 6 shows a slant gauge used to measure pressuredifferences.

9. The various pressures of air applied to an air-conditioning system are relatively small and cannot bemeasured in pounds for an accurate reading. Total,static, and velocity pressures for airflow in air-conditioning systems are usually measured in inches ofwater. The pressure of air is measured by the applicationof a gauge calibrated in inches of water on the scale foraccurate reading, as shown in figure 4.

10. The gauge in figure 4 contains a free-flowingliquid. The connections are extended by flexible tubingto the air passages and the atmosphere. The differencein pressure of the air will cause the liquid in the tube torise or fall, indicating the pressure on the scale in inchesof water according to the connections of the gauge.

11. Pitot Tube. Total and static pressure for airflowthrough a duct system can be measured by a pitot tube.Use of a pitot tube is illustrated in figure 7. The staticpressure can be found by subtracting the velocity pressurefrom the total pressure. The static pressure subtractedfrom total pressure will equal velocity pressure for air in aduct system. The total (dynamic) pressure is equal to thestatic and velocity pressures.

12. The use of the pitot tube for pressure indicationshould be done with care. The tube should be located sothat an average condition of airflow

Figure 6. Measuring resistance of air filters.

15

will be measured in the interior of the duct. The tubeshould not be placed in a sharp turn in the duct, in arestricted area, in an offset, or in a section having varyingairflow. Also avoid contact with material or substancesthat would obstruct air pressure to the pitot tube opening.

13. The pitot tube consists of two tubes, one sealedwithin the other. The opening of the pitot tube whichfaces toward the airflow measures the total pressure. Theother opening of the pitot tube has airflow sweep acrossthe opening so as to measure the static pressure. Thevelocity is determined by the differential reading on thegauge which is connected to the double pitot tube.

14. A certain pressure for airflow in ducts isrequired to cause motion and to overcome resistance andfriction in the ducts.

15. Static pressure will vary according to the surfacearea with which the air is in contact. Some factors are:condition of air passages, construction and installation,dampers, interior design, length of duct system, leakage,eddy currents, and pulsation of airflow throughout theinstallation.

16. Anemometer. The anemometer, shown infigure 8, is used to measure air velocities at the openingof the air duct. The anemometer is moved across theentire area of the duct opening for a period of 1, 2, or 3minutes and the average velocity in feet of air iscalculated or measured.

17. The anemometer should be used with precautionand care. It requires frequent calibration or adjustmentto maintain it for accurate measurement of air velocitiesat duct openings.

Figure 7. Measuring airflow with a pilot tube.

Figure 8. Use of the anemometer.

18. Kata Thermometer. A kata thermometer is analcohol thermometer developed for determining very lowair velocities. The bulb of the thermometer is heated inwater until the alcohol rises to a reservoir above thegraduated tube. The time for the liquid to cool 5° F. isobserved by the use of a stopwatch, and this time is ameasure of the air movement.

19. Velometer. The velometer is an instrument thatis calibrated to read directly in feet per minute. Thevelocity pressure readings are converted by use of aformula without the necessity for timing. The velometermay be placed directly in the airstream or may beconnected through a flexible tube to special jets whichpermit taking velocity readings in locations where itwould be very difficult to use an anemometer or pitottube. The velometer accuracy is within 3 percent and ismuch quicker to use than other instruments designed forthis purpose.

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Review ExercisesNOTE: The following exercises are study aids. Write your

answers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the text. Do not submit your answers for grading.

1. What degree on a centigrade thermometer isequivalent to 60° on a Fahrenheit thermometer?(Sec. 4, Par. 4)

2. What degree on a Fahrenheit thermometer isequivalent to 40° on a centigrade thermometer?(Sec. 4, Par. 4)

3. How many B.t.u.'s would be required to raisethe temperature of 8 pounds of cast iron 4°?(Specific heat of cast iron is 0.119)(Sec. 4, Par.6)

4. What term is applied to the sum of sensible heatand latent heat? (Sec. 4, Par. 8)

5. If the air is dry, which thermometer will indicatethe highest temperature, a dry-bulb or a wet-bulbthermometer? (Sec. 4, Pars. 10 and 11)

6. After whirling a sling psychrometer, how willthe wet-bulb thermometer reading compare to

the dry-bulb thermometer if the wet-bulb wickwas dry while whirling? (Sec. 4, Par. 11; Sec. 5,Par. 3)

7. Will the difference in the dry-bulb thermometerreading and the wet-bulb thermometer readingbecome greater or less as the relative humiditydecreases? (Sec. 4, Par. 11; Sec. 5, Par. 3)

8. What two factors must be known in order todetermine the relative humidity? (Sec. 5, Pa. 3)

9. What type of water should be used to wet thewick of a wet-bulb thermometer? (Sec. 5, Par.6)

10. If the total pressure of an air-conditioningsystem remains constant and the air ductsbecome partially clogged, will the static pressureincrease or decrease? (Sec. 6, Pars. 8-11)

11. If the total airflow pressure is equal to 20 inchesof water and the static pressure is equal to 4inches of water, what is the velocity pressure?(Sec. 6, Par. 11)

12. Is it possible to determine static pressure with avelometer? (Sec. 6, Pars. 11 and 19)

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CHAPTER 3

Design and Installation Factors

COST REDUCTION has become an important part ofmilitary policy. How can you contribute to thisprogram ? You may be called upon to install an airconditioner or to calculate the heat load of a building. Ineither case, your skill can determine the savings. If yourunit is undersized, it will have to be supplemented withanother unit. If it is oversized, the running cost will behigh. You may install the correct size unit but use poorduct insulation. Once again you are defeating thepurpose of cost reduction.

2. In this chapter you will study heat loads, theselection of a good location for the condensing unit,insulation, and calculating a heat load.

7. Heat Sources1. Heat that must be removed from a building

arises from various sources. Some of this heat is gainedthrough walls, doors, partitions, windows, ceilings, androofs, and is caused by the difference in the temperaturebetween the conditioned and unconditioned areas.Remember, heat always travels from the warmer to thecooler mass. Engineering formulas are used to calculateheat transmission. Glass and door areas are not used incalculation of wall area but are considered in heattransmission calculations in a separate formula.

2. In calculating wall area, use the length (ft.) ofexposed wall measured on the inside and the height ofceiling.

3. Consideration must be given to constructionmaterials of the walls and ceilings. For example, brickconstruction has a different heat transfer characteristicthan wood.

4. Special tables are used in determining heattransmission through various building materials. Listedbelow are some heat sources that must be considered incooling load computations.

5. Solar Effects. Heat that is transmitted byradiation through glass is absorbed by inside furnishingsand surfaces. When the sun's rays strike glass, the glasswill absorb a small percentage of the sun's energy, butmost of the energy passes through the glass and causesan increase in heat.

6. The solar heat which passes through glass isabsorbed by interior furnishings, walls, and floors. Thisheat is quickly given up to the air. Some of the solarheat absorbed by thick walls and doors will not dissipateits heat readily, but will continue radiating heat even afterthe sun has set. Because of this, the heat load is morecontinuous.

7. The intensity of the sun radiation on walls andglass varies with the time of day, the season, and thedirection the walls and windows face. All the abovefactors must be considered when you are computing solarheat transmission.

8. Heat delivery by sun radiation through glass maybe reduced by use of awnings, Venetian blinds, or shades.Any type of shade will help reduce the load on air-conditioning equipment.

9. Special formulas and tables have been devised todetermine solar heat transmission through glass and walls.

10. Infiltration and Ventilation. Heat and moistureare transmitted into a building by infiltration andventilation. Air enters by leakage through window anddoor cracks, through doors or windows opened, andthrough porous walls. Special tables have been devised todetermine the infiltration of air through window openingsand for finding the volume of air entering from doortraffic. All the above factors must be considered incooling load computations.

11. Occupants. Heat load from occupants willcause an increase in sensible and latent heat. Theamount of heat transmitted will vary with the degree ofactivity of the occupants.

12. Equipment. Heat load transmitted byequipment used in a building will vary with the type andoperation. Electrical and mechanical equipment will havea major effect on total heat load. Tables have beendeveloped that give values of common heat sources. Allof the tables referenced in the preceding paragraphs maybe found in the American Society of Heating, Refrigerating,and Air Conditioning Engineers' Guide.

13. Listed above are a few of the major heattransmission sources that must be considered wheninstalling an air-conditioning unit. The total heat

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load must be established before an air-conditioning unitcan be installed in a building. All heat transmissionsources must be used in figuring out the total heat load.When the heat load has been determined, an air-conditioning unit of correct tonnage can be installed andthe proper cooling can be maintained in the building.

8. Selecting Location1. The following are major considerations in

selecting the location for air-conditioning equipment.2. Availability of Space. Equipment should be

located in the place most suitable for it. It may benecessary to compromise the ideal location with theactual one and to locate equipment in the space which isavailable.

3. Ambient Temperatures. Ambient temperaturerefers to the air temperatures surrounding therefrigeration equipment, such as the condensing unit andother parts of the system. Avoid extreme ambienttemperatures, either too warm or too cold.

4. Excessively warm locations result in high heatleakage and service loads. High ambient temperature cangive high condensing pressures with consequent loss ofcapacity. An ambient temperature of 10° F. abovenormal may increase the heat load and decreaseequipment capacity to the extent where the operatingtime increases 25 percent above normal.

5. Consideration must be also be given to lowtemperature to which the equipment may be exposed.Do not install water-cooled equipment in locations colderthan 40° F. to avoid frozen water-lines in condensers.

6. Ventilation. Proper ventilation is very importantfor carrying heat away from the condensing equipment.It is most important to air-cooled equipment which usesair to carry heat away from the condenser. It is alsoimportant to water-cooled equipment, even though waterremoves heat from the condenser. The heat from thecompressor and motor must be carried away by thesurrounding air, and this cannot be accomplished withoutadequate ventilation. Keep all ventilation facilities suchas doors and windows free of barriers and other obstaclesso that the air can be properly circulated.

7. Radiant Heat. Part of the heat given off by ahot object such as a hot stove, boiler, furnace, or even ahot brick is radiant heat. Avoid installing refrigerationequipment near such objects. It is not Sways possible,but the extra load of radiant heat should be avoidedwhenever possible.

8. Electric Supply. Be sure that the proper poweris furnished before selecting a location. Check the

electric supply to be sure there is correct voltage,frequency (cycles per second), phase, and capacity of thewiring. If the equipment has a motor requiring 220-volt,60-cycle, 3-phase alternating current, it will not run on110-volt, 60-cycle, single-phase alternating current.Consult a qualified electrician on suitability of electricsupply for motors installed on equipment. Motors shouldnever be connected to a source of electric current untilyou are sure that available current is the same as thatspecified on the nameplate.

9. Water Supply. Before selecting a location forwater-cooled refrigeration equipment, check the watersupply for available capacity and maximum temperature.The capacity of a water-cooled condensing unit dependsupon whether or not it is supplied with enough coolcondensing water. Rated capacities of condensing unitsare usually based on 75° F. condensing water beingavailable. Higher temperature water requires more watersupplied. If enough water is not available, the capacity ofthe condensing unit may be reduced 5 percent for each5° F. higher than the correct temperature of condensingwater.

10. Drain. Check location of suitable drain and itscapacity before installing equipment. Drain lines areconnected to sewers through an open sight connection.If possible, trap and vent the sewer branch to guardagainst entry of sewer gas into the rooms.

11. Accessibility. When selecting the location ofequipment, consideration must be given to its accessibilityfor cleaning and servicing. It is not always possible tofind all the room you actually need. Whenever possible,leave enough room for a workman to get at all sides ofthe unit, and enough room to permit removal orreplacement of any major assemblies, such as motor,compressor, and condenser.

12. Accessibility to those parts of equipment subjectto preventive maintenance and inspections, or requiringreadjustment, repair, or replacement must be given specialpreference. See that oil wells of motors, belts, air-cooledcondensers, service valves, and especially suction servicevalves on compressor, gauge, and gauge ports, controls,and nameplate data are readily accessible.

9. Insulation1. Insulation represents the composite covering

which consists of the insulating material, lagging, andfastening. The insulating material offers resistance to theflow of heat; the lagging, usually of painted canvas, is theprotective and confining covering placed over theinsulating materials; the fastening attaches the insulatingmaterial to the piping and to the lagging.

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2. Insulation Temperatures. Insulation covers awide range of temperatures, from the extremely lowtemperatures of the refrigerating plants to the very hightemperatures of boilers. No one material could possiblybe used to meet all the conditions with the sameefficiency. Cork, rock wool, or hair felt is used for lowtemperatures. Such basic minerals as asbestos, carbonateof magnesia, diatomaceous earth, aluminum foil,argillaceous (clay-like) limestone, mica, fibrous glass, anddiatomaceous silica are employed for high temperatures.Because of its high degree of refractoriness, diatomaceoussilica forms the base of practically every high temperatureinsulating material.

3. Insulating Material Requirements. Thefollowing quality requirements for the various insulatingmaterials are taken into consideration in thestandardization of these materials:

a. Ability to withstand highest or lowesttemperature to which it may be subjected without itsinsulating value being impaired.

b. Sufficient structural strength to withstandhandling during its application, and mechanical shocksand vibrations during service without disintegration,settling, or deformation.

c. Stability in chemical and insulationcharacteristics.

d. Ease of application and repair.e. No hazard in case of fire.f. Low heat capacity, when used for boiler wall

insulation, so that starting-up time may be minimized.

4. Insulating Materials. Listed below are a few ofthe more popular insulations that you may encounter inair-conditioning work.

5. Cork: Cork in block sections or compressedboard form, coated with a special retardant cover, is used(where authorized) for temperatures below 50° F. It useis generally limited to refrigeration spaces where it willnot be a serious fire hazard. Molded cork pipe covering,treated with a fire-retardant compound, is used onrefrigerant piping.

6. Mineral or rock wool. Mineral or rock wool is afiber made by sending a blast of steam through moltenslag or rock. The rock fibers are usually from dolomiterock, composed of calcium and magnesium oxides andsilicates. The fibers are brittle, of low tensile strength,light in weight, and resistant to moisture. The fibers areused in wire-reinforced pads for insulating large areas.

7. Hair felt. Hair felt, 1 inch or more in thickness,may be used in any service where the temperatures donot rise above 119° F. When combined with heavyasphalt-impregnated paper, this material is used on cold-water lines where the temperature range is from 50° to

90° F. When suitably waterproofed, it may be used forrefrigerator piping.

8. Asbestos. Molded sheets, pads, blankets, or tapesof long asbestos fibers are suitable for insulatingtemperatures up to 850° F. This insulation material ischeaper and lighter than the diatomaceous earth type andis durable and rugged. The pads or blankets are used forinsulating flanges or valves which must be taken downfairly often, as well as for turbine casings. The pads aremolded to fit any shape, and the outer surface is fittedwith metal hooks to facilitate their installation andremoval. The blankets are generally made 1 inch thick,40 inches wide, and fitted with hooks. The tapes areused for covering ½a- inch and smaller piping with curvesand bends. They can be used for temperatures up to750° F.; they tend to reduce fire hazards, but they havepoor insulating quality.

9. Magnesia and asbestos. The magnesia andasbestos mixture, of which about 85 percent is magnesia,is the most common material used for hot piping. It isobtained commercially in pulverized form, in sheets, inshaped blocks, and in cylindrical sections for standardpipe sizes. Its principal features are low heatconductivity, ease of application, light weight, low cost,and chemical inactivity. The chief disadvantage is thelimited temperature range, as the mixture calcines anddecomposes at about 500° F.

10. Diatomaceous earth. The diatomaceous earth(sand formed from skeletons of certain microscopicplants) materials are combinations of the earth andmagnesium or calcium carbonates, bonded together withsmall amounts of asbestos fibers. These materials areheavier, more expensive, and less insulating than others,but their high heat resistance allows their use fortemperatures up to 1500° F. When practical, pipecoverings are made up with this material as an inner layerand with an outer layer of the magnesia-asbestos material.This lightens the overall weight.

11. Aluminum foil. Aluminum foil is the mosteffective insulating material for high temperatures. Thefoils are produced commercially from pure aluminum andare supplied in long, thin sheets, some 12 inches to 16inches in width. The covering is light, particularly forlarge piping for which it is best suited. There is very littleuncleanliness connected with the installing or removingof aluminum foil; it is easy and economical tomanufacture and, because of its light weight and lowinertia, it stands up well under vibration or shock.

12. There is more than one method of applyingaluminum foil. The following is the most common ofthese methods. One or more layers of foil are wrappedabout the material to be insulated, leaving a 3/8-inchairspace between each layer, and with a sheet metal coverto protect the foil. The airspace between the layers offoil is kept by

20

first hand-crinkling the foil so that its surface becomesuneven. This type of insulation serves to reduce to aminimum any convection current present in the airpockets.

13. The chief objections to the use of aluminum foilfor insulation are the weight of the sheet metal covernecessary to cover the assembly and the high skillnecessary for its application or repair.

14. Fibrous glass slabs. Fibrous glass slabs are usedwidely for insulating living quarters. The glass fibers inthe pressed slabs are 4 inches or more in length and0.0005 to 0.0008 inch in thickness. The slabs have a lowmoisture-absorbing quality and offer no attraction toinsects, vermin, fungus growth, or fire. The slabs arefirst cut to shape, then secured in place by mechanicalfasteners (as quilting pins), and finally covered with glasscloth facing and stripping tape (held in place by fire-resistant adhesive cement).

15. The insulating cements. Insulating cements arecomposed of many varied materials. These materialsdiffer among themselves as to heat conductivity, weight,and physical characteristics. Typical of these variationsare the asbestos cements, diatomaceous cements, andmineral and slag wool cement. These cements are lessefficient than other high-temperature insulating materials.They are valuable for patchwork emergency repairs andfor covering small irregular surfaces (valves, flanges,joints, etc.). The cements are also used for a surfacefinish over block or sheet forms of insulation, to sealjoints between the blocks, and to provide a smooth finishover which asbestos or glass cloth lagging may be applied.

16. Insulation Application. In applying insulatingmaterial, care should be taken that air does not circulatethrough the insulation, that moisture is kept fromreaching the insulation, and that the insulation will notmove or slip.

17. All sections or segments of the pipe coveringsshould be tightly butted at joints and secured with wireloops, metal banks, or lacing. Block insulation should besecured with 1/8-inch steel wire and galvanized meshwire or expanded metal lattice. Insulating cement is usedto fill all crevices, to smooth all surfaces, and to coat wirenetting before final lagging is applied.

18. Moistureproofing is important for insulation overheated surfaces. Even though the temperature of theinsulation dries off moisture, the heat loss is increaseddue to the evaporation. Moisture also impairs manyinsulating materials. This moistureproofing is also veryimportant for low temperatures. At very lowtemperatures, the insulation should be air-sealed.Moisture drawn into low-temperature insulationcondenses and freezes, thus lessening the efficiency andeventually causing disintegration.

19. The same insulating material employed on thepiping may be used on pipe fittings, flanges, and valves.These components require additional consideration duringinstallation.

20. When a permanent type of insulation is appliedto a piping 4 inches and larger in size, a block insulation1 inch thinner than that on the adjacent piping may beused for the bodies of flanged fittings and valves, for theentire surface of a threaded fitting, for the entire surfaceup to the bonnet of screwed valves, and for the flanges.The total thickness of insulation on the valve or fitting ismade equal to that on the adjacent piping by applyinginsulating cement. The pipe insulation should be stoppedshort of the flanges and leveled off to enable the flangebolts to be removed. On piping under 4 inches in size,the insulation of the fittings may consist entirely ofinsulating cement, the same thickness as that of theadjacent piping.

21. When a removable type of insulation is applied,the flanges should be insulated with asbestos felt pads,sectional pipe insulation of the same thickness as that onadjacent piping, or block insulation 1/2 inch thinner thanthat on the adjacent piping and covered with 1/2 inch ofinsulating cement.

22. Installation Precautions. The following generalprecautions should be observed with regard to theapplication and maintenance of insulation:

a. Fill and seal all air pockets and cracks. Failureto do this will cause large losses by conduction andconvection currents.

b. Seal the ends of the insulation and taper off to asmooth, airtight joint. Sheet metal lagging should beused at joint ends and at other points where insulation isliable to damage. Flanges and joints should be cuffedwith 6-inch lagging.

c. Cotton duck covering, fitted over insulation,should be smooth and well sewn (not less than threestitches per inch). It should be covered with two coats oflead and oil paint. Too much paint will cause the cottonduck to crack and split.

d. Keep moisture out of all insulation work.Moisture is an enemy of heat insulation as much as it isof electrical insulation. Any dampness increases theconductivity of all heat-insulating materials.

e. Insulate all hangers and other supports at theirpoint of contact with the pipe or other units they aresupporting. Failure to insulate these supports will cause aconsiderable quantity of heat to be lost by conductionthrough the support.

f. Sheet metal covering should be kept bright andnot painted unless the protecting surface has beendamaged or worn off. The radiation from bright-bodiedand light-colored objects is con-

21

siderably less than from rough and dark-colored objects.g. Once installed, heat insulation requires careful

inspection, upkeep, and repair. Any lagging andinsulation that is removed to make repairs should bereplaced just as carefully as when originally installed. Oldmagnesia blocks and sections broken in removal can bemixed with water and reused in the plastic form. Save allold magnesia for this use.

h. Insulate all flanges with removable forms. Theforms can be made up as pads of insulating materialwired or bound in place, and the flange can be coveredwith sheet metal casings which are in halves and easilyremovable.

10. Making Survey for Air-Conditioning Installation1. We will now-relate the facts we have discussed

to a specific air-conditioning installation. This installationis at Denver, Colorado. You may be called upon todetermine the size of a unit needed at your installation.The primary difference between this example and yourbase would be the mean wet- and dry-bulb temperatures.

2. Cooling Load Requirement. In this chapter wehave discussed heat sources in an area that is to beconditioned. These heat sources are as follows:

a. Solar heat load on walls, roofs, and glass.b. Human heat load.c. Infiltration and ventilation.d. Machinery,3. Upon adding the values of the heat sources

listed, you would have a load that is called total internalcooling load.

4. Special consideration must be given to locationof a room or building when cooling load calculations arebeing made. The interior load may change from oneportion of the buildings to another. Varied heat loadsfrom equipment, solar radiation, and occupants will alterthe calculations. When calculating heat load, alwaysconsider the peak load that could be reached in thebuilding.

5. With a building that may have a changeable heatload. an experienced air-conditioning man cannot statedefinitely the time of day that the building cooling loadwould be at a maximum. Therefore, it is necessary tocalculate cooling load for this establishment at severaldifferent periods during the day. These times should bechosen when the values of the various heat sources are attheir maximum.

6. Calculation of Cooling Load. Problems incalculating cooling load can be done with mathematical

exactness or by rough approximate estimates. Themethod that is used to calculate a cooling load dependsupon the purpose for which the results will be used.Rough estimates are very inaccurate, and your plant maynot meet cooling load requirements.

7. The mathematical exactness method is quitecomplicated and requires very accurate informationregarding construction materials. It may require thedrilling of holes through walls, roof, and floors todetermine construction materials. Some principles usedin determining the size of refrigeration plant required fora typical installation are mentioned below.

8. Rate of Heat Flow Through Walls. The rate atwhich heat is transmitted through walls, floors, and roofsis dependent on the following factors:

a. Unit heat transfer coefficient (U-factor). TheU-factor depends on wall material and thickness.

b. Area of the heat-transmitting surface.a. The temperature difference between the sides of

the wall.9. The heat transfer coefficient is the combined

rate of transmission of any substance expressed in B.t.u.per hour per square foot of area per degree Fahrenheitmean temperature difference. It combines the amount ofheat transmitted by radiation, conduction, and convectioninto a single quantity referred to as the U-factor.

10. The basic heat transfer formula is expressed asQ = UA (T1 – T0). This formula is used in mostcalculations.

Q = solar radiation in B.t.u. per hour.U = coefficient of heat transfer in B.t.u. per square

foot taken from tables.A = area of transmitting surface in square feet.T1 = inside building temperature.T0 = outside building temperature.11. Another formula that is used in calculations for

radiation through glass is expressed as Qg = Ag Ig FgAg = area of glass in square feet.Ig = coefficient of heat transfer for glass taken from

table.Fg = glass radiation factor.

The following is a list of heat loads:a. Load from solar radiation.b. Sky radiation.c. Outdoor-indoor temperature differential for glass

areas, exterior walls, partitions, ceilings, and floors.d. Load due to ventilation.e. Load due to heat sources within the conditioned

spaces such as occupants, lights, fans, power, and otherheat-generating equipment

22

12. This data is available in ASHRAE Guides andmanufacturers' manuals.

13. Specifications of Building To Be AirConditioned.

Location: Denver, Colo.Southern exposure.

South wail: Front 20 ft. inside, 12 ft. high; plate glass10 ft. x 6 ft. high; door 3 ft. x 7 ft. (glass).

North wall: 20 ft. inside, 12 ft. high; plate glass, 2windows 5 ft. x 3 ft. high; wooden door 3ft. x 7 ft.

East wall: 20 ft. inside, 12 ft. high; plate glass, 2windows 5 ft. x 3 ft. high.

West wall: 20 ft. inside, 12 ft. high; plate glass. 2windows 5 ft. x 3 ft. high.

Floor: Wooden lath and covered with 1/4-inchlinoleum laid on wooden floor.

Ceiling: 4-inch wooden rafters, metal lath plasterbelow with 1-inch wooden roof deck,covered with roofing paper.

Occupancy: 5 employees (manual labor).Equipment: Electric lights 2000 watts, two 1/2-hp.

motors, stove burner heating water, coffeeurn (12 inch).

Outside design condition: Denver, Colo., 95° F. dry bulb and78° F. wet bulb.Inside design condition selected as 81° F. dry bulb and 68° F.wet bulb.All walls are constructed of 12-inch brick plastered inside.Heat gain calculation at peak load approximately 1:00 p.m.

South wall 20 ft. X 12 ft. = 240 sq. ft. gross.Area glass l0 ft. X 6 ft. = 60 sq. ft.Area door 3 ft. X 7 ft. = 21 sq. ft.Transmission coefficient for glass 1.13.Transmission coefficient for brick .34.Heat transmission through wall = 757 B.t.u./hr.Heat transmission through glass = 1280 B.t.u./hr.Heat transmission by solar radiation = 3300 B.t.u./hr.South wall heat gained = 5337 B.t.u./hr.North wall 20 ft. X 12 ft. = 240 sq. ft. gross.Area glass 5 ft. X 3 ft. (2) 30 sq. ft.Area door 3 ft. X 7 ft. = 21 sq. ft.Heat transmission through wall = 900 B.t.u./hr.Heat transmission through glass = 475 B.t.u./hr.Heat transmission through door = 332 B.t.u./hr.North wall heat gained = 1707 B.t.u./hr.Fast wall 20 ft. X 12 ft. = 240 sq. ft. gross.Area glass 5 ft. X 3 ft. (2) 30 sq. ft.Heat transmission through wall = 1000 B.t.u./hr.Heat transmission through glass = 475 B.t.u./hr.Fast wall heat gained = 1475 B.t.u./hr.West wall 20 ft. X 12 ft. = 240 sq. ft. gross.Area glass 5 ft. X 3 ft. (2) 30 sq. ft.Heat transmission through wall = 1000 B.t.u./hr.Heat transmission through glass = 475 B.t.u./hr.West wall heat gained = 1475 B.t.u./hr.Floor 20 ft. x 20 ft. = 400 sq. ft.Transmission coefficient is .24.Heat transmission through floor = 1344 B.t.u./hr.Ceiling 20 ft. x 20 ft = 400 sq. ft.

and roofTransmission coefficient is .32Heat transmission through roof = 1790 B.t.u./hr.Solar radiation through roof = 3460 B.t.u./hr.Total heat gain through roof = 5250 B.t.u./hr.Total heat gain through walls and roof is equal to5337 +F 1707 + 1475 4- 1475 + 1344 + 5250 =16,588 B.t.u./hr.Heat gain from occupants.Sensible heat loss = 200 B.t.u./hr.Latent heat loss = 460 B.t.u./hr.Total heat gain sensible (5 men) = 1000 B.t.u./hr.Total heat gain latent (5 men) = 2300 B.t.u./hr.Total heat gain from equipment.Heat gained from coffee urn.Latent heat = 1200 B.t.u./hr.Sensible heat = 1200 B.t.u./hr.Electric motor = 640 B.t.u./hr. (sensible)Electric light = 7816 B.t.u./hr. (sensible)Stove burner = 3150 B.t.u./hr. (sensible)

= 3850 B.t.u./hr. (latent)Total sensible heat gain from

equipment = 18.566 B.t.u./hr.Total latent heat gain from

equipment = 5.050 B.t.u./hr.Approximate total cooling load in B.t.u./hr.

Sensible Latent1. Through walls and solar radiation 16.5882. Human load 1.000 2,3003. Equipment 18,566 5.050

36,154 7,35014. An additional factor of 10 percent is often added

as a safety factor to the sensible load to take care ofadditional energy that may be added to the internalsystem. Therefore, total cooling load requirementsbecome:

Sensible load = 36.154 X 1.10 = 39,769 B.t.u./hr.Latent load = 7,350 B.t.u./hr.Total cooling load = 47.119 B.t.u./hr.

47,119Refrigeration = 12,000 = 3.9 tons of refrigerationequivalent to cooling load. This calculation isapproximate because there are other factors that must beconsidered in cooling load calculations. Ventilation,infiltration, and duct losses are part of your cooling loadrequirements and will change in value with eachinstallation.

15. Cooling load formulas and tables can be foundin American Society of Heating, Refrigerating and Air-Conditioning Engineers' Guide, Fundamentals andEquipment, 1963.

Review Exercise

NOTE: The following exercises are study aids. Write youranswers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the text. Do not submit your answers for grading.

23

1. Calculate the following wall areas. The outerdimensions are 10' x 14' and the walls are 8"thick. (Sec. 7, Par. 2)

2. A complaint is received from one of the basehousing units. The user tells you that the airconditioner will not cool down the housesufficiently.. After questioning her, you findthat she has all the drapes on the windows openand also that she didn't start the unit until noon.What directions should you give the user? (Sec.7, Pars. 5-8)

3. Which type of heat load will affect humidity themost? (Sec. 7, Par. 11)

4. The normal ambient temperature for acondensing unit was 80° F. when it wasinstalled. Additional units have been installed inthe area and the ambient temperature is now105°. This increase in temperature is affectingthe operating time of the units. How could youcorrect this situation? (Sec. 8, Pars. 4 and 6)

5. How much efficiency would a condenser lose ifthe water supplied to it was 85° F. instead of75° F.? (Sec. 8, Par. 9)

6. Which type of insulation should you use on a40° F. cold storage room? (Sec. 9, Par. 5)

7. The strainer on a low-pressure steam coilinstallation must be removed periodically forcleaning. How would you insulate the strainer?(Sec. 9, Par. 8)

8. A new barracks is being built and you are calledupon to insulate it. What type of insulationwould you use and why would you select thatparticular type? (Sec. 9, Par. 14)

9. The temperature of the hot water at the heatingcoil is 130° F. The design coil temperature is180° F. and the supply temperature from theboiler is 185° F. Why is the temperaturedropping from 185° to 130° F.? (Sec. 9, Par.18)

10. You are insulating a 2-inch pipe with 3/4-inchinsulation. How much insulation and what typeof insulation should you put on a globe valve?(Sec. 9, Par. 20)

11. Find the solar radiation through a brick wall 20'x 40' which has a 30° F. temperaturedifferential. (Sec. 10, Pars. 10 and 13)

12. Find the heat gain of a brick wall 10' x 12'which has two 2' x 4' glass windows. Theoutside temperature is 94° F. and the insidedesign temperature is 72° F. (Sec. 10, Par. 13)

13. Which type of heat load will give off the mostlatent heat gain? (Sec. 10, Par. 13)

14. Find the total cooling load when the sensibleload is 42,156 B.t.u.'s and the latent heat load is8,750 B.t.u.'s. (Sec. 10, Par. 14)

15. What size unit would you install if the sensibleload is 57,150 B.t.u.'s and the latent load is 9,170B.t.u.’s? (Sec. 10, Par. 14)

24

CHAPTER 4

Self-Contained Package Air-Conditioning Units

MOST SERVICEMEN call these air conditionerswindow- and floor-mounted units. You will find thatthey are identified in this manner throughout the chapter.The self-contained units differ from the remote unitsdiscussed in another volume (Equipment Cooling) of thiscourse in that one housing contains all the components.

2. These units are usually found in offices or in aportion of a building that is separate. One example is apanel room in a heat and power building. It would beimpractical to air-condition the entire building because ofthe heat load from the diesel engines, furnaces,refrigeration equipment, etc. The panel room housesgauges, recorders, and various instruments that the dutyengineer observes to oversee plant operation.

3. You will study the window- and floor-mountedunits. Included under these topics are installation,operation, maintenance, and various components peculiarto these systems.

11. Window-Mounted Units1. The window-mounted air conditioner is a

factory-made incased assembly, designed as a unit formounting in a window or through a wall. It is designedfir free delivery of conditioned air to an enclosed spacewithout ducts.

2. This air conditioner has a prime source ofrefrigeration and dehumidification, and a means ofcirculating and cleaning the air. It may also includemeans for ventilating and heating. The basic function isto provide comfort by filtering, cooling, dehumidifying,and circulating the room air; and to provide ventilationby introducing filtered outdoor air into the room orexhausting room air to the outside. If heating isprovided, steam coils, hot water coils, or electricresistance heaters may he used, or the conditioner may bedesigned as a heat pump unit. We will discuss the heatpump later in this volume.

3. Sizes and Classifications. The coolingcapacities of window-mounted air conditioners range

approximately from 4000 to 36,000 B.t.u./hr. or 1/3 to 3tons. Remember, whenever you want to convert B.t.u.'sto tons, 12,000 B.t.u.'s equals 1 ton. The sizes hadcommonly been designated in terms of horsepower, butthis proved to be inaccurate because various refrigerantsdiffer in cooling efficiency. Capacities (sizes) are nowmeasured in B.t.u./hr.

4. Most of these air conditioners are designed ashousehold appliances and are equipped with line cordsthat may be plugged into a standard I15-230 plugreceptacle with a ground. Conditioners requiring 115volts are usually limited to a current load of 12 amperes,which is the maximum allowable load of a single -outlet15-ampere circuit. This is in compliance with theNational Electric Code (N.E.C.). 1959. A very popular I115-volt model is one which is rated at 7.5 amperes.This rating allows the unit to he plugged into anystandard 115-volt 15-ampere circuit. large units,generally over 10.000 B.t.u./hr. are designed as 230-voltunits, which can be plugged into a 230-volt circuit withinthe limitations set forth by the National Electric Code.

5. There are also units which are designed for ;application to the particular power supplies you mayencounter in countries outside the United States.Remember, always read the nameplate before plugging ina unit.

6. Many mounting designs are available forparticular applications of window-mounted airconditioners. A few of the various mountings are:

a. Inside flush mounting. The interior face of theconditioner is approximately flush with the inside edge ofthe window sill.

b. Balance mounting. The unit is installedapproximately half inside, and ha1f outside the window.

c. Outside flush mounting. The outer face of theunit is flush or slightly beyond the outside wall.

d. All-in-mounting. The unit is completely insidethe room so that tie window can be closed.

e. Upper sash mounting. The unit is mounted inthe top of the window.

25

f. Built-in mounts. The mounts are used forinstalling units in the walls of hotels, motels, residences,etc.

7. There are many special mounts that can be used.We will not discuss each one. A special mounting maybe used for casement windows, swinging windows, andoffice windows with swinging units, to permit windowwashing. Special mounts are also used for transomwindows over doorways.

8. Installation and Operation. Installationprocedures vary because units can be mounted in severalways. It is important to consider the most suitablemounting for the installation, the user's desires, andexisting building codes.

9. Electrical system. We've already discussed theelectric power source needed for a 115- or 230-volt unit,but we didn't cover proper grounding of the unit. Allwindow type air conditioners, regardless of voltage oramperage rating, must be grounded. Most units areequipped with grounding type male plugs. These plugsare used with a grounded (three-prong) 115-voltreceptacle.

10. The National Electric Code states that non-current-carrying metal parts which are liable to becomeenergized shall be grounded under one or more of thefollowing conditions:

a. Where permanently connected to metal-cladwiring.

b. When in a wet location and not isolated.c. When within reach of a person standing on the

ground outside the building.d. When in a hazardous location.e. When in electrical contact with metal or metal

lathe.f. Where the voltage is more than 150 volts to

ground.11. Can you think of any installation that wouldn't

require grounding? It's very doubtful that you can, soremember, whenever you install a unit, make sure it'sgrounded.

12. Can you plug the unit into any receptacle? Yes,if the total load of the air-conditioning equipment doesnot exceed 80 percent of the current rating of the branchcircuit, provided the voltage rating is satisfied. If thebranch circuit also feeds lighting units or other appliances,the total load of the air conditioner shall not exceed 50percent of the current rating of the circuit.

13. If a question about the power source orgrounding arises, contact an electrician. He is a specialistin electricity, as you are in refrigeration. Themanufacturer includes instruction sheets with his unit.You will find these helpful in mounting and installing theunit.

14. Through-the-wall units with steam or hot wirecoils must be wired in or connected with armored cableor conduit. The electrician should complete this task.When the cooling unit can be removed withoutdisturbing the heating system, it is customary to provideenough wire to facilitate installation and servicing withoutdisconnecting the entire air conditioner.

15. The electrical system of an air conditionerconsists of an appliance cord, plug, thermostat, fan motor(s), starting relay, starting capacitor, running capacitor,compressor motor, overload protector, and switches thatcontrol the flow of current to the various electricalportions of the system. Now we will discuss eachelectrical component.

16. The appliance cord and plug are manufacturedas one unit. The cord is usually a three-wire cord withtwo current-carrying conductors and a ground wire. Theconductor should be the correct size to carry the currentthat is necessary to operate the unit. The round thirdterminal of the service plug (1 15-volt) is the groundingterminal and should never be removed.

17. The control switch (es) mounted on the controlpanel of the unit directs electric current to variousportions of the system to satisfy the desires of the user.All functions of the switch (es) are clearly marked.

18. The thermostat automatically controls theoperation of the compressor motor, fan motor, andaccessories to provide the comfort conditions required bythe user. This control is accomplished by a feeler bulblocated in the return airstream. The ambient temperatureof the feeler bulb causes a bellows in the thermostat toexpand or contract. This in turn causes the thermostatswitch to open or close electrical contacts to thecompressor and fan motors. Some thermostats havepositions which afford the user constant operation.

19. The fan motor(s) and fans provide the forced airthrough the evaporator and condenser coils. The fanmotor always operates when the compressor is running.

20. The starting relay, used frequently on 115-voltunits, may be of the voltage operated type with normallyclosed contacts. The relay magnetic coil is wired inparallel with the starting winding of the compressormotor. Voltage developed by motor operation at 80 to 90percent of full speed is impressed on the relay coil, whichopens its contacts. With the relay contacts closed, thestarting and running capacitors are wired in parallel witheach other and in series with the compressor motorstarting winding. When the relay contacts open, thestarting capacitor is disconnected, but the runningcapacitor remains in series with the starting winding.

21. The starting capacitor stores electricity andprovides power for extra compressor motor startingtorque at the starting instant. This capacitor remains inthe circuit for only a brief

26

Figure 9. Room air-conditioner wiring diagram.

interval at startup. If the starting relay fails to quicklytake the starting capacitor out of the circuit, it is possiblethat the starting capacitor will fail.

22. The running capacitor, which can be a heavy-duty, oil-filled capacitor, is used in the circuit to reducethe current requirements of the compressor motor powerfactor.

23. The compressor motor may he of various types.Two common types arc the capacitor start-capacitor runand the permanent-split capacitor motor. Thepermanent-split capacitor motor doesn't use a startingrelay.

24. The motor overload protector is used on allcompressor motor:; to protect them against excessivecurrent draw and abnormal heat. The overloadprotector is usually mounted either under the terminalblock cover or on top of the compressor against the shell.The overload protector consists of a bimetal strip withcontacts and, in some cases, a heater clement. Excessivecurrent draw will cause the heater element or the bimetalstrip itself to heat up, thereby causing the contacts toopen. Excessive compressor shell temperature can alsocause the bimetal strip to open the contacts.

25. When the bimetal contacts open, they remainopen until the temperature of the heater and/orcompressor shall have cooled enough to cause a reset

action. When making replacements, never use anunknown type of overload protector. Replace theoverload protector with a like unit, as shown in anillustrated parts breakdown for that specific airconditioner. Be certain, also, that the overload protectorhas good metal-to-metal contact with the compressorshell to protect the compressor motor.

26. The operation of the electrical system for allwindow-mounted air conditioners are similar. We willuse an air conditioner with a two-speed fan motor as anillustration. Figure 9 shows the wiring diagram for thisair conditioner. With the pushbutton switch in thecooling position, current is applied to the fan motorRemember, the fan motor always operates when thecompressor motor is running. Current also passes thethermostat. If the thermostat is calling for cooling, thecompressor motor is energized. The compressor starts torotate, helped by the starting capacitor. The startcapacitor is in the circuit when the compressor motorstarts, because the starting relay contacts on the voltagetype relay are always closed when the relay coil is notenergized. When the compressor reaches 80 to 90percent of full speed, the voltage developed in the startwinding is impressed upon the relay coil. The voltagedeveloped at this speed is enough to pull the relaycontacts open and take the starting capacitor out

27

of the circuit. The compressor continues to run on therun winding and the running capacitor. Now we'll turnour thoughts to the refrigeration cycle.

27. Refrigeration cycle. The refrigeration cycle of anair conditioner consists of a compressor motor, condensercoil, evaporator coil, capillary tube, strainer assembly, andits interconnecting tubing.

28. The fan motor(s) circulates air to remove theheat picked up by the refrigerant system. The condenserfan brings in outside air and forces it through thecondenser coil, where it picks up heat and carries it to theoutside air. The evaporator blower wheel recirculatesroom air, passing it through the cold evaporator, wheremoisture in the air condenses and its heat is absorbed bythe refrigerant in the cooling system. The refrigerantsystem is hermetically sealed.

29. The compressor pumps the low-pressure gasfrom the interior of the compressor shell into thedischarge line. The high-pressure gas, with its heatconcentrated by compression, is forced into thecondenser. The high-pressure gas is raised intemperature, at the compressor, above the outside airtemperature which is being used to cool the condenser.The hot gas gives up its heat as it passes through thecondenser coils. The hot refrigerant gas gives up enoughheat to condense to a liquid. High-pressure liquidrefrigerant leaves the condenser. It now passes through astrainer assembly. The strainer is an enlarged tube with avery fine mesh screen to remove any foreign particles.The high-pressure liquid now enters the capillary tube.The capillary tube acts as a restrictor (metering device)and separates the high side of the system from the lowside.

30. The high-pressure liquid refrigerant is reduced inpressure by the restrictive action of the capillary tube.The liquid enters the evaporator low-pressure area, whichwas created by the suction stroke of the compressor. Theliquid refrigerant exposed to this reduced pressure beginsto boil and absorb more heat from the recirculated warmair. The boiling action of the liquid refrigerant progressesthroughout the evaporator tubes, picking up heat as ittravels. This low-pressure liquid now changes to low-pressure gas which is drawn out of the evaporator andback to the compressor, where the cycle is repeated.

31. Airflow system. The airflow system consists of afan motor(s), evaporator blower wheel, condenser fan(s),and their housings. Two-speed or variable-speed fans andcontrols may be used. Many air conditioners have twoseparate airflow systems. These systems are the room aircooling, ventilating circuit and the condensing or outsideair circuit. They are separated by a bulkhead and gasket

32. To maintain peak performance, it is importantthat the filter, evaporator coils, and condenser coils be

kept clean. Any restriction of airflow to thesecomponents will result in reduced unit capacity.

33. The evaporator blower wheel draws the room airthrough the louvered grille of the cabinet, through thefilter, then through the evaporator coils. It is thendischarged back into the room.

34. The condenser fan draws its air from theoutside. It then passes this air over the compressor andelectrical controls and out the condenser, where it carriesoff heat collected from the room air and the variouscomponents of the air conditioners. The condenser fanis often equipped with a slinger ring that removescondensate water collected from the evaporator. This isdone by slinging the condensate on the condenser whereit evaporates.

35. Air seals are provided around the outer edge ofthe evaporator housing and in the front grille to restrictairflow to its proper path. Now that we've discussed thevarious systems, we can relate the troubleshootingtechniques you might use on them.

36. Trouble Diagnosis and Testing Procedures.There are various pieces of test equipment you could useto diagnose trouble. These are the ohmmeter, volt-wattmeter, load checker, test starting set, andpsychrometer.

37. Electrical system. If you find the air conditionerinoperative with the service cord plugged into a powersupply, check the electrical outlet with a test lamp orvoltmeter. If power is not available, you must check thepossible faults which we will discuss in the nextparagraphs.

38. First, examine the fuse box for blown fuses(circuit breaker for tripped breakers) and be certain fusesare of the time-delay type and of the correct size asindicated on the front of the air conditioner. If no poweris available at the line side of the fuse box, tell the userand advise the electric shop.

39. To determine if the power supply is adequate,check the voltage at the power source with a voltmeter.The voltage must be within ±10 percent of the voltagerequired with the air conditioner on maximum cooling.A load checker may be used to simulate the wattage thatthe air conditioner will draw.

40. If the correct voltage is available at thereceptacle, examine the service plug to be sure it ismaking good contact with the receptacle. Remove theservice plug from the receptacle and check the servicecord with an ohmmeter. Full continuity should exist thelength of the service cord. You must check all theconnections within the air conditioner to insure that theyare securely fastened and making good contact.

41. Another possible fault could be grounding. Thethird wire of the service cord (green) is grounded to thechassis and will eliminate the

28

Figure 10. Test starting set.

shock hazard. Internal grounds will cause fuses to blowor, if of a minor extent, cause excessive powerconsumption and breakdown of components. Groundedcurrent-carrying paths in the electrical system should notbe allowed to exist.

42. Grounds nay he eliminated by testing each wireor component with an ohmmeter. With the ohmmeteron a high scale, test between the wire and any brightmetal of the chassis, such as the copper tubing. Nocontinuity should exist between the wire or electricalcomponents and the chassis. Continuity should existbetween the round prong of the service plug and thechassis. This is the grounding line.

43. To check the starting relay, disconnect theservice cord from tie power source and expose the relay.With the ohmmeter, test the relay switch contacts forcontinuity. If there is no continuity, replace the relay.Another malfunction that may exist within the relay is agrounded relay coil. If an ohmmeter check indicates nocontinuity across the coil, the relay must he replaced.

44. The starting and running capacitors may bechecked with an ohmmeter. The capacitors must beremoved from the circuit and fully discharged beforemaking a test. You can discharge the capacitors byshorting the capacitor leads. The first indication youshould observe with the ohmmeter is a short circuit(needle will swing toward 0) and then the reading shouldslowly change to indicate a resistance reading ofapproximately 100,000 ohms.

45. To test the compressor motor, you must firstdisconnect the service plug from the power source. Nowattach the test starting set, shown in figure 10, to thecompressor motor. You may use the starting capacitoron the air conditioner if you've already tested it andfound it not malfunctioning. The test set plug should beconnected to the same or equivalent power supply usedfor the air conditioner. Push down the push buttonswitch, then release it. The compressor motor shouldstart. If it didn't start or if it blew fuses repeatedly,replace the compressor. If the compressor starts, the

trouble is in one or more of the other electricalcomponents.

46. One of the components that may be faulty is theoverload protector. The contacts in the overloadprotector are normally closed. An ohmmeter checkbetween any two of the terminals should indicatecontinuity. If no continuity exists, the overload protectormust be replaced. If the overload protector opensrepeatedly and the voltage, wattage, and temperature ofthe compressor are normal, substitute a known goodprotector. If the opening continues, the trouble lieselsewhere.

47. Another component that may be malfunctioningis the thermostat. The thermostat test is very easilymade. Set the thermostat to its coldest position and testfor continuity between the two terminals. If there is nocontinuity, the thermostat must be replaced. Make surethat the thermostat feeler bulb is above 70° F. To makeit that warm, hold the bulb in your hand.

48. We have discussed the troubleshootingtechniques that you may use on the electrical system ofan air conditioner. Remember that all conditioners arenot alike. Therefore you should always refer to themanufacturer’s manual and wiring diagrams.

49. Refrigeration system. In the event a usercomplains of insufficient cooling or no cooling, there aresome logical checks you should make beforetroubleshooting the refrigeration system. One would bethe electrical system and the other the airflow. We’vealready discussed the electrical system, so we’ll discusswhat to check in the airflow.

50. Check the airflow system for cleanliness of thefilter, evaporator coils, and condenser coils. If these areclean, check the fan speed. The fan speed may bechecked with a portable tachometer. These malfunctionsare the primary causes of low or no cooling. If noelectrical or airflow fault is found, you must thentroubleshoot the refrigeration system.

51. The correct refrigerant charge will be indicatedby normal amperage draw. The amperage may be foundon the data plate. Low amperage draw is an indication oflow refrigerant charge, while a high draw may be anovercharge or dirty condenser.

52. Another test you may accomplish to checkrefrigerant charge is the "frost back test." With the unitrunning, block the evaporator air inlet with a piece ofcardboard. After a period of time, the suction lineshould frost back to the compressor. A partial frost backindicates a low refrigerant charge. If the suction linedoes frost back to

29

Figure 11. Thermometer placement for performance tests.

the compressor, the air conditioner should be given aperformance test to determine that it is operating to itsfullest efficiency.

53. Two dry-bulb thermometers, one psychrometer,and a wattmeter are needed for this test. Before youmake the test, allow the unit to operate at full capacityfor one-half hour. Be sure that the damper doors in theunit and any doors or openings to the room are closed sothat no outside air is allowed to enter the room and nocooled air is allowed to leave the room.

54. Next, you must position the louvers on the frontof the air conditioner so that the conditioned air flowsupward. Now you place the various instruments that youwill use to obtain values for comparison withperformance data and tables in their pertinent places.One of the dry-bulb thermometers is suspended in thecondenser inlet airstream. You must be careful not toallow it to make contact with any metal parts and mustkeep it out of the direct rays of the sun. The remainingdry-bulb thermometer is supported in the approximatecenter of the evaporator air outlet stream. Thepsychrometer is placed in the center of the evaporatorinlet airstream. Be certain that you wet the wet-bulbwick. The wattmeter is connected in series with thepower supply to the air conditioner. Figure 11 shows thevarious locations of these instruments during theperformance test of a window air conditioner. Read the

temperatures and wattage draw when the lowest wet-bulbtemperature is obtained. All readings should be taken asnearly simultaneously as possible.

55. At this point you need a helper stationed outsideto read the inlet condensing air temperature. Thesereadings are now compared to the performance tablevalues. Each manufacturer has these tables available foreach model he produces. You cannot perform the testaccurately without them. These tables containinformation such as condenser inlet air temperature,evaporator inlet air temperature (wet bulb), evaporatorinlet-outlet air temperature differential, total wattage, lowside pressure, and high side pressure.

56. Let's assume the following readings were takenfrom an Anthony make air conditioner, model 21-9588-06. This is a 1-H.P. 115-volt unit. Figure 12 is theperformance table for this air conditioner. Thecondenser air inlet temperature is 95° F. and theevaporator air inlet temperature is 67° F. You must nowrefer to figure 12. Under column A we find the 95° F.condenser air inlet temperature, and in column B we findthe 67° F. evaporator air inlet temperature. When wefollow to the right from the 67° F. reading, we find thefollowing values:

Evaporator Inlet-Outlet Air Temperature Differential17°-24° F.

30

Figure 12. Performance chart.

Watts Total to Unit 1290-1470 Watts.Low Side Pressure 71-75 p.s.i.g.High Side Pressure 300-330 p.s.i.g.57. From these performance values, we find that the

normal air temperature drop across the evaporator is 17°-24° F. If the temperature drop exceeded 24° F., youcould Suspect a dirty filter, incorrect fan speed, or arestriction in the evaporator airflow. A temperature lessthan the minimum (17° F.) could indicate low linevoltage, air leakage from normal paths, or a dirtycondenser

58. Well, let's say that we've found the airconditioner operating at its fullest capacity and the userstill complains of insufficient cooling. One possibleremedy would be to replace the unit with a unit of largercapacity or install an additional unit.

59. If you have determined, by use of theperformance test, that the air conditioner is not operatingat its fullest capacity, you must troubleshoot the unit.The last possible fault you should troubleshoot is a lowrefrigerant charge. If leak testing is necessary, you coulduse the following test procedures.

a. Expose the unit and the refrigerationcomponent.

b. Examine all components and tubing for breaks,cracks, and traces of oil. (Since a small amount of oiltravels through the system with the refrigerant, a trace ofoil would be a good indication of a leak.)

c. With a halide leak detector, probe every joint fora leak source.

60. A soap-water solution may also be used forfinding leaks. Finding a leak is one of three conditionsthat may make entry into the sealed unit necessary. The

other conditions are restrictions and compressor and/orcompressor motor failure.

61. Service Procedures. The service literaturepublished by the manufacturer contains replacementdiagrams for each model he produces. The knowledgeyou will gain from a close examination of these diagramswill help make the replacement of any part of an airconditioner readily possible. A step-by-step procedure isusually given on more difficult part removal items. Thisprocedure is usually brief and keyed to a picture bynumbers. To replace parts that you've removed, reversethe sequence you used to remove them.

62. Filters. Dirty filters, along with low voltage, arethe major causes of poor performance of an airconditioner. You should familiarize the user with thelocation of the filter and with the fact that it should beinspected frequently for cleaning or replacement.Aluminum mesh type filters may be cleaned as often asnecessary without damage. The filter should be cleanedwith hot soapy water, then flushed thoroughly. After thefilter is dry, it should be recoated with a domesticmineral oil or commercial type metal filter coating. Youshould explain to the user that the entire surface of bothfaces of the filter requires recoating. This procedureincreases the dirt enhancing quality of the filter.

63. Condenser and evaporator. The coils of thecondenser and evaporator should be cleaned periodically.You may accomplish this task with a soft brush or avacuum cleaner.

64. Condensate disposal system. In order to reducethe humidity in the conditioned area, an appreciableamount of air-conditioner capacity is required. This isreferred to as latent load,

31

Figure 13. Sectional view of an air-cooled floor-mounted air conditioner.

while the actual reduction of air temperature is called thesensible load.

65. As the room air passes through the evaporatorcoils, the moisture in the air condenses. This condensatethen drains back to the condenser housing sump, where itis drained or picked up by the slinger ring of thecondenser fan. The slinger ring blows the water into thehot surfaces of the condenser coil. This moisture helpsto cool the condenser coil as it is vaporized and blowninto the outside air. It is important to keep thecondensate drain clear to allow free drainage of thiswater. Proper slope of the air conditioner to the rearprovides for this drainage.

12. Floor-Mounted Units1. The floor-mounted or console air conditioner

may have either water-cooed or air-cooled condensingunits. The air-cooled model is gaining in popularity dueto water restrictions. Figure 13 shows an air-cooledconsole unit. Note how the condensate from theevaporator coil is entrained in the condenser air. We alsofind that two separate fans and motors are used to movethe air, while the window-mounted air conditionernormally uses one Fresh air or ventilating air is bypassedfrom the condenser air just as it leaves the condenserfan.

2. This air conditioner is applied to either resi-

32

dential or commercial use. The latter is used for comfortcooling and control of temperature and humidity formanufacturing purposes. In residences it is used forcomfort only.

3. We won't discuss each component of thevarious systems which make up the air-conditioner, asthey are directly related to components that we've alreadydiscussed. Instead, we will discuss each system brieflywith more thought concentrated on components peculiarto this unit.

4. Refrigeration System. The refrigeration systemconsists of a compressor, cooling coil, condenser,expansion device, and the necessary interconnectingtubing. The components peculiar to this system are thedifferent types of condensers, expansion devices, andcompressor capacity controls.

5. Condensers. We will discuss the various types ofcondensers that you may find on this air conditioner andhow they are cleaned. The most common is the air-cooled condenser. The air-cooled condenser consists ofcoils over which air is blown. Refrigerant cooling isobtained by adequate condenser surface and maximumsir circulation over the outside coil and fin surface.

6. Ordinary brushes and mild soap cleaningsolutions will remove the usual dirt and dust deposited onair-cooled condensers. However, in some applications,the materials that may be deposited on the condensercannot be removed by these means. If this situationarises, you can make a good cleaning agent by mixing 1/2pound of trisodium phosphate with 1 gallon of water.After you use an acid or alkaline solution, you shouldrinse or flush the condenser with large quantities of clearwater.

7. Another problem that you may have to copewith is carbon deposits. There is more danger torestricted airflow in using a solution which would loosen,or partially loosen, the carbon deposit than there wouldbe in using a solution which would not remove all of it.The loosened particles could plug the condenser. Themost satisfactory method of cleaning the inner portion ofthe condenser is to use superheated steam. You will findthat this method will do a thorough job of removing allthe loosened material from the inside of the condenser,and will prevent formation of any oxide or other materialon the coils and fins. One precaution you should applywhen using superheated steam is to be sure that thetemperature of the steam is not above the melting pointof any of the materials from which the condenser isconstructed.

8. One water-cooled condenser (shell-and-tube)consists of a gas type sealed shell containing a copper coilor tubes. The hot refrigerant gas is admitted into the

condenser shell and flows down over the condenser tubesin which cooling water is circulated. The gas condenseson the surface of the tubes and runs to the bottom of thecondenser shell. These condensers are used frequentlywhere the cooling load is heavy and the ambienttemperature may rise over 90° F.

9. The tubes in a shell-and-tube condenser have atendency to become coated, and sometimes even filled,with deposits (magnesium, calcium, etc.) from the waterthat passes through them. The safest method that youmay employ for cleaning a water tube is soft metalbrushes. You should start with a small diameter brushand increase the diameter of the brushes until one that isjust the diameter of the inside of the tube is used. Donot attempt to apply force to the brush rod with ahammer. A large piece of scale or deposit could causethe rod to deflect and rupture the tubing wall oppositethe deposit. Most tubes are not galvanized or coatedwith a surface-protecting material, so you should oil eachtube after it has been cleaned. This may be done bydrawing an oil-soaked cloth through the tube. The filmof oil will prevent oxidation and will be washed off in ashort time after water has run through the tube.

10. Another water-cooled condenser is the double-pipe condenser. This type of water-cooled condenser hasbecome very popular because of its performance and itsconvenience of manufacture. The double-pipe condenserconsists of one pipe inside a large pipe. The ends of thelarger pipe are sealed against the inside pipe so thatliquids or gases may be directed through its entire length.

11. The water usually passes through the inner pipe,and the refrigerant through the outer. The counterflowprinciple is usually employed so that the lowesttemperature water comes in contact with the lowesttemperature refrigerant This type of operation couldlower the leaving refrigerant temperature to the sametemperature of the incoming. water. However, a 10°differential is considered satisfactory.

12. Liquid cleaning with solutions of strong causticsoda or mild muriatic acid is practically the only cleaningmethod you can use on this type of water-cooledcondenser. You should test the strength of the solutionbefore you use it, as it may weaken the tube. Themanufacturer usually recommends the strength ofsolution you should use on his condenser and how to testit. When you mix the solution, always add the acid tothe water and wear the appropriate safety equipment.

13. On large equipment, double-pipe condensers aremade of iron pipe. These are so constructed that thereturn ells can be removed. This exposes the inner tubeso that it may be cleaned with a brush, as were the tubesin the shell-and-tube condenser.

33

Figure 14. Evaporative condenser.

14. The repair of water-cooled condensers is usuallyperformed by the manufacturer, unless it is otherwisespecified in the manufacturer's service publication. Inthis case a detailed breakdown and procedure are given.

15. The evaporative condenser, shown in figure 14,consists of a fan and motor, eliminators, condensing coil,waterpump, spray headers and nozzles, a water sump, anda makeup water valve.

16. The operation of the evaporative condenser issimilar to that of the cooling tower except thatcondensing coils are installed in the airflow. The twotypes of evaporative condensers are the draw-through andthe blow-through. We will limit our discussion to thedraw-through type, as it is the most popular of the two.

17. First, we'll discuss the operation of theevaporative condenser. In the draw-through type, wefind that the air enters at the sump plenum, then flowsup through the condenser coils, spray nozzles,eliminators, and out to the atmosphere. The entering aircauses the water on the condensing cods to evaporate.The evaporation process removes heat from therefrigerant within the coils, causing the high-pressure gas

to condense. The moisture-laden air then passes on tothe eliminator plates, which are closely spaced surfacesthat provide abrupt changes in airflow direction. Themoisture particles are deposited on these surfaces anddrained back to the sump. Effective elimination ofmoisture from the leaving air is essential to preventprojection of mist which can deposit moisture onsurrounding surfaces. The carryover of water particleswill also tend to form scale on the fan blades, therebycausing operational difficulties.

18. Scale is formed by low soluble salts.Polyphosphate chemicals may be added to the water,thereby enabling the water to become supersaturatedwithout precipitation of scale-forming solids. Let's lookat figure 14 again. We haven't mentioned the bleed tubewhich allows some of the pump discharge water to -drainoff. What does that have to do with the formation ofscale? Before we answer that question, let's state a fewfacts.

a. The water contains suspended solids (salts, iron,etc.).

b. The cycles of concentration increase each timethe water circulates through the system (evaporization ofwater).

c. The dissolved solids are less soluble because ofchanges in the water temperature (water heated bycondenser coils).

19. With these facts in mind, we find that bleedingoff some of the recirculated water and replenishing itwith makeup water will decrease the amount of solidssuspended in the cooling water. Remember, the cycle ofconcentration is the ratio of bleedoff water hardness tomakeup water hardness. The bleedoff water rate isdirectly proportional to the amount of water beingevaporated. Continuous bleedoff, with rates based oncondenser evaporation rate and makeup water hardness,decreases the precipitation of scale on the condenser coil.Scale on the condenser coil surface decreases the heattransmission through the surface and may reduce airflow.

20. Normally the next component in therefrigeration system is the receiver. Since you are alreadyfamiliar with the receiver, we will bypass our discussionof it and proceed to the expansion device.

21. Expansion device. The most common expansiondevice used on this air conditioner is the thermostaticexpansion valve with an external equalizer anddistributor. The external equalizer is used to compensatefor the pressure drop across the evaporator. A valve withan internal equalizer would cause the evaporator to starvebecause the pressure sensed under the valve diaphragmwould be the inlet evaporator pressure. Let's set up anexample to clarify our discussion.

22. Figure 15 shows a thermostatic expansion valve(for refrigerant -12) with an internal

34

Figure 15. Thermostatic expansion valve with aninternal equalizer.

equalizer. We are going to give the evaporator a 10-p.s.i.g. pressure drop across it. We find that the pressureacting on the lower side of the diaphragm is 37 p.s.i.g.,which is causing the valve to close. With the valvesuperheat spring set at a compression equivalent to 10° F.superheat or a pressure of 9.7 p.s.i.g., the requiredpressure above the diaphragm to equalize the forces is46.7 p.s.i.g. (37 + 9.7). Using your temperature-pressurechart, you will find that this pressure corresponds to asaturation temperature of 50° F. Therefore, therefrigerant temperature at point C must be 50° F. if thevalve is to be in equilibrium. Since the pressure at thispoint is only 27 p.s.i.g. and the corresponding saturationtemperature is 28° F., a superheat of 22° F. (50 - 28) isrequired to open the valve. This increase in superheatmakes it necessary to use more of the evaporator surfaceto produce this higher superheated refrigerant gas.Therefore the amount of evaporator surface available forabsorption of latent heat of vaporization of therefrigerant is reduced. The evaporator would be starvedbefore the required superheat is reached. This starvingeffect increases as the load increases.

23. To compensate for an excessive pressure dropthrough an evaporator, you should install a valve of theexternal equalizer type, with the equalizer line connectedinto the evaporator (at a point beyond the greatestpressure drop) or into the suction line (on the compressorside of the remote bulb installation). The most commoninstallation is in the suction line. When this valve isused, the true evaporator outlet pressure is exerted underthe diaphragm. The operating pressures on the valvediaphragm are now free from any effect of the pressuredrop, and the valve will respond to the superheat of therefrigerant gas leaving the evaporator.

24. The same pressure drop still exists through theevaporator; however, the pressure under the diaphragm isnow the same as the pressure at point C, or 27 p.s.i.g.

The required pressure above the diaphragm forequilibrium is 27 + 9.7, or 36.7 p.s.i.g. This pressurecorresponds to a saturation temperature of 40° F., andthe superheat required is now 40 - 28, or 12° F. The useof an external equalizer has reduced the superheat from22° F. to 12° F. Thus the capacity of a system will beincreased.

25. The expansion device shown in figure 16 is thethermostatic expansion valve and pressure dropdistributor. This arrangement is used on the multicircuitevaporator to assure that an equal mixture of gas andliquid refrigerant reaches each evaporator circuit Anexternal equalizer is used to compensate for the pressuredrop caused by the distributor. An internally equalizedvalve would limit the action of the valve and cause theevaporator to starve.

26. The maintenance and servicing of this valve issimilar to that of the common thermostatic expansionvalve.

27. Our next discussion will cover the variouscapacity controls that may be used on the system. Theseare the hydraulic cylinder unloader and the compressorbypass valve.

28. Capacity controls. The hydraulic cylinderunloader is used to improve compressor capacity controlduring light load conditions. The unloader accomplishesthis by holding open the suction valve on some cylindersand allowing the piston to draw gas on the downstroke,but on the upstroke it returns the gas to the suction linewithout compressing it.

29. On single-step unloader systems, one-half of thecylinders are unloaded, while on multistep unloaders thecylinders are unloaded in increments. These incrementsdepend on the number of cylinder in the compressor.Figure 17 and 18 illustrate a typical unloader mechanism,loaded and unloaded. The bottom portion of each figureshows the capacity control actuator.

30. To understand the complete operational cycle,you should think of the unloader mechanism

Figure 16. Single outlet expansion valve with apressure drop distributor.

35

Figure 17. Hydraulic cylinder unloader (loaded).

as two distinct components, the capacity control actuatorand the cylinder unloader mechanism.

31. The capacity control actuator reacts to variationsin refrigeration load requirements and transmits them tothe cylinder unloader mechanisms which load or unloadthe cylinders. To perform this dual function, the capacitycontrol actuator consists of a pressure-sensing device,which is sensitive to variation in suction pressure; and avalving mechanism, which regulates the oil pressure tothe various cylinder unloader mechanisms.

32. The pressure-sensing devices (fig. 17) consist ofa chamber (1) connected to the suction line (2) and abellows (3), which is vented to atmosphere (4). Thefunction of the pressure-sensing device is to maintain, asnearly as possible, a predetermined suction pressure. Thispressure is the maximum pressure required to satisfy therefrigeration system. The specific set point is maintainedby a balance of forces. Suction pressure is balanced

against a combination of atmospheric pressure and forcefrom a spring (5). The amount of spring tension isadjustable by a set screw (6). When the system requiresless than full-refrigeration load, the suction pressure willfall below the predetermined point, causing an unbalancewithin the device, and the unloading cycle willcommence. The drop in suction pressure permits thebellows (3) to expand, forcing the plunger (7) against thelever (8), and moving it downward. The downwardmovement of this lever opens the regulated orifice (9).The opening and closing of this orifice controls theaction of the valving mechanism.

33. The function of the valving mechanism is tosupply each of the cylinder unloaders with oil underpump pressure when full compressor capacity is requiredand to relieve this pressure when the cylinders are tooperate unloaded. This valving mechanism consists of ahydraulic cylinder, containing an annularly grooved,floating piston

Figure 18. Hydraulic cylinder unloader (unloaded).

36

(11). The annular grooves are constantly fed with oilthrough a line (23).

34. Above the piston is a chamber (12) vented tothe crankcase through an orifice (10). Below the piston isanother chamber (13) connected to the annular groovesin the piston by an orifice (14). It is also connected tocrankcase pressure through a regulated orifice (9).Located within the hydraulic cylinder is a spring (15),which tends to move the floating piston toward the lowerchamber.

35. Under full capacity operation, as shown in figure17, the regulated orifice (9) is shut off and the oilpressure in the lower chamber (13) increases because oilunder pump pressure is being supplied through orifice(23). This pressure overcomes the force of the spring(15) and the floating piston (11), which rises in thecylinder. As it rises, the annular grooves in the floatingpiston coincide in sequence with lines 16-1, 16-2, and 16-3 to the cylinder unloaders, providing them with full oilpressure and permitting them to operate at full capacity.To make figures 17 and 18 as simple as possible, only line16-1 is connected to a cylinder unloader mechanism.Lines 16-2 and 16-3 are, in reality, connected to identicalmechanisms; and while this discussion is concerned withonly one unloader mechanism, we could extend it tocover them all.

36. When full compressor capacity is not required,the regulated orifice (9) is opened through the movementof the lever (8); oil bleeds through it, and pressure withinthe lower chamber approaches crankcase pressure, asshown in figure 18. Under these circumstances, the forceof the spring (15) overcomes the pressure in the lowerchamber, and the floating piston (11) is moveddownward so that lines 16-1, 16-2, and 16-3 becomeconnected in sequence to crankcase pressure through theorifice (10). The spring-loaded ball (24) permits thepiston to move only in distinct increments, one groove ata time.

37. In this manner the valving mechanism suppliesor withdraws from each cylinder unloader the oil pressurethat operates the unloader mechanism.

38. When oil from the forced feed lubricatingsystem flows through line 16-1 from the valvingmechanism to the cylinder unloader, it enters the annularchamber (17). The inner wall or unloader cylinder isfirmly anchored to the cylinder liner; the unloader piston(18), however, is free to move. The up and downmovement of this unloader piston raises and lowers thetakeup ring (19), which, in turn, raises and lowers thesuction valve lift pins (20).

39. Under full capacity operation (fig. 17), oil flowsinto the annular chamber (17) under pressure sufficientto contract the unloader piston springs (21 ). When oil

pressure forces the springs to contract, the unloaderpiston (18) moves down, and takeup ring (19) and thesuction valve lift pins (20) move with it. This permitsthe suction valve (22) to function normally and thecylinder operates at full capacity. When the compressoris to operate at less than full capacity (fig. 18), crankcasepressure flows through the orifice (10), which allows thepressure in the annular chamber (17) to dissipate; thecylinder unloader springs (21) expand, lifting the unloaderpiston (18). This raises the takeup ring (19) and the valvelift pins (20), and holds the suction valve (22) open sothat the controlled cylinder is operating in an unloadedcondition.

40. You will find that the compressor unloader issensitive to variations in suction pressure. It may bedesirable to unload the compressor in response tovariations in air temperatures. This can be accomplishedalso through the use of pneumatic or electric controls.By introducing controlled air pressure from a pneumaticthermostat to the inside of bellows (3), in place ofnormal atmospheric pressure, the suction pressure atwhich unloading begins can be varied, thus makingcompressor operation responsive to variations in airtemperature as sensed by the pneumatic thermostat.When electric control of unloading is desired, the screw(6) is replaced by a mechanical device. It resets thesuction pressure which causes unloading to begin. Thisdevice is driven by an electric motor that is positioned byan electric thermostat.

41. The hydraulic cylinder unloader may be adjustedto maintain a balance between the load and compressorcapacity. This adjustment is usually made after aninstallation. We will discuss this adjustment, but youshould follow the manufacturers recommendations whileperforming this task on your specific piece of equipment.Before you adjust the capacity control, you must load thesystem either naturally or artificially until design suctionpressure is reached with the adjusting screw (6) turned allthe way out. Now, slowly open the suction shutoff valveuntil the suction pressure is 2 p.s.i.g. below the designpressure.

42. The next step is to turn the adjusting screwclockwise until the first cylinder unloads. Just before itunloads, the control oil pressure will drop toapproximately 26 p.s.i.g. below oil pump pressure. Thecontrol oil pressure is present in line 16-1. When thecylinder unloads, there will be a distinct change in thesound of the compressor and in the amperage beingdrawn. The remaining cylinder are automaticallyunloaded as suction pressure drops.

43. Maintenance of the cylinder unloader can befound in the manufacturer's publications. We

37

Figure 19. Direct-acting solenoid valve.

will not discuss it as it may not be applicable to yourequipment and would only tend to confuse you.

44. The next capacity control device you willencounter is the compressor bypass valve. A specialsolenoid hot gas valve, installed in a bypass line aroundone or more cylinders, will provide compressor capacitycontrol. The valve may be operated either by athermostat or a switch. A check valve is required in thedischarge line beyond the bypass line to prevent a reverseflow of discharge gas from other cylinders.

45. There are two types of solenoid valves you mayfind on this installation: the direct-acting, shown in figure19, and the pilot-operated, illustrated in figure 20. In thedirect-acting type, the pull of the solenoid coil opens thevalve port directly by lifting the pin out of the valve seat.Since this valve depends solely on the power of thesolenoid coil for operation, its port size for a givenpressure differential is limited by the solenoid coil size.

46. Therefore large solenoid valves are usually of thepilot-operated design. In this type the solenoid plungerdoes not open the main port directly, but merely opensthe pilot port (A). Pressure trapped on top of the piston(B) is released through the pilot port, thus creating apressure unbalance across the piston (B). The pressureunderneath is now greater than that above and the pistonmoves upward. This opens the main port (C). To closeport C, the coil is deenergized, causing the plunger todrop and close the pilot port (A). Now the pressuresabove and below piston (B) equalize. The piston (B) willnow close the main port (C). The pressure differenceacross the valve, acting upon the area of the valve seat,holds the piston in a tightly closed position.

47. You may have to select a solenoid valve whileperforming your routine duty. You'll find that there aremany applications for this device. When you select a

valve, you should know the fluid to be controlled, capcity (in tons of refrigeration), maximum operatingpressure differential, maximum working pressure, andelectrical characteristics. The capacities of solenoid valvesare given in tons of refrigeration at standard conditionsfor the various refrigerants, with a pressure drop acrossthe valve of 2 or 4 p.s.i.g. for liquids and 1 p.s.i.g. forgas. Most manufacturers publish tables extending thesecapacities for higher pressure drops.

48. You'll find that all solenoid valves are rated interms of the maximum operating pressure differential(m.o.p.d.) against which the valve will open. Let's use anexample here to clarify our discussion. With the valveclosed and an upstream pressure of 150 p.s.i.g. against adownstream pressure of 50 p.s.i.g., the pressuredifferential across the valve would be 150 - 50, of 100p.s.i.g. The m.o.p.d. of this valve must be equal to, or inexcess of, the valve (100 p.s.i.g.).

49. Now that you've selected the valve, the next stepis to install it. Remember, most solenoid valves aredesigned to operate in a vertical position and, therefore,must be installed in a horizontal line. Special valves areavailable to be installed in any position. When installingthe valve, be sure the arrow on the valve body points inthe direction of refrigerant flow. The final step in theinstallation of the valve is the electrical wiring. You mustbe sure that the voltage, type of current, and frequencymarked on the valve nameplate are compatible with thesystem voltage, current, and frequency.

Figure 20. Large pilot-operated solenoid valve.

38

50. Should the valve fail to function afterinstallation, the following are some of the probable causesof failure and suggestions for correcting them:

a. Solenoid valve fails to open.(1) System operating pressure too high. The

m.o.p.d. rating of the valve may be lower than the actualdifferential. A valve with a higher m.o.p.d. must beused.

(2) Valve body or internal parts are warped.These faults are caused by excessive wrench torque orhigh brazing temperatures.. You must replace thedamaged part or the entire valve as required.

(3) Dirt or sludge causing valve to stick. Youmust dismantle the valve and completely clean theinterior and component parts. Use an approved cleaningagent.

(4) Low voltage. Check the power supply witha voltmeter. The applied voltage must be at least85.percent of the rated voltage given on the nameplate.For example, a 115-volt solenoid requires at least 97.75 or98 volts. If the voltage Is lower than 98 volts, the causeof the voltage drop must be determined and corrected.Common causes of voltage drops are undersized supplylines, other loads connected in series with the coil, looseor faulty connections, and faulty control switches ordevices.

(5) Coil burnout. Excessive voltage is theprimary cause of coil burnout. Coils should not besubjected to voltages higher than 10 percent above therated nameplate voltage-126.5 volts for a 115-volt ratedcoil. High ambient temperatures can also cause coilburnouts. Use a special high-temperature coil if yourevaluation established overheating as the fault.

b. Solenoid valve fails to close.(1) Valve body or internal parts are warped.

Cause and correction same as (2) under subparagraph ,Solenoid valve fails to open.

(2) Dirt or sludge causing valve to stick. Causeand correction same as (3) under subparagraph a.

(3) Electrical circuit closed. Troubleshootelectric circuit and repair or replace the faulty component(switch, relay, thermostat, etc.).

(4) Congealed oil causing valve to stick.Refrigerant oil should be of the proper type fortemperature range of the system. Corrections is the sameas (3) under subparagraph .

51. These service hints are general in nature and canbe applied to most solenoid valves. If problems arisebeyond this scope, you should consult the manufacturer'sservice manual.

52. There are many other components that wemight discuss but they are peculiar to one manufactureronly.

53. We will now enter into discussion of the air-handling system. The components that will be discussedare fans, motors, and drives.

54. Air-Handling System. The air-handling systemon the floor-mounted air conditioner in similar to that onthe window-mounted type except that the componentsare larger.

55. Fans. The two types of fans common to this airconditioner are the propeller and centrifugal fans. Thepropeller fan consists of a propeller, or disk wheel, withina mounting ring or plate; the centrifugal fan consists of afan rotor, or wheel, within a scroll type of housing.

56. In some air-conditioning systems, it is desirableto vary the volume of air handled by the fan. This maybe done by a number of methods. Where the change ismade infrequently, the pulley, or sheave, on the drivemoor or fan may be changed to vary the speed of the fanand alter the air volume. Dampers may be placed in theduct system to vary the volume. Variable-speed pulleysor transmissions, such as fan belt change boxes, orelectric or hydraulic couplings, may be used to vary thefan speed. Fan volume can also be varied with the useof variable-speed motors and variable-inlet vanes.

57. From the standpoint of power consumption, thereduction of fan speed is most efficient when a directmechanical method is employed. Inlet vanes save somepower, while dampers save the least

58. When considering first, or initial cost, you'll findthat damper are usually the lowest. Air supply demandsand noise will dictate which type of control to install

59. Fan selection as to size and type depends oncapacity, static pressure or system resistance, air density,type of application, arrangement of system, prevailingsound level, nature of load, and type of motive poweravailable. To help you make your choice, a fanmanufacturer will furnish you information on differentsized fans working against different static pressures.Some of the important information is as follows: (1)volume of air (c.f.m.), (2) outlet velocity, (3) r.p.m., (4)brake horsepower, (5) tip or peripheral speed, and (6)static pressure. The most efficient operating point isusually shown by either boldface or italicized figures inthe capacity tables.

60. Many fan applications and the correspondingtypes of fans commonly used are listed in the followingparagraphs.

61. Unitary systems are equipped with centrifugal orpropeller fans,, the later usually being limited to therelatively small suspended type (window-mounted) whereno duct work is involved. Fans for units havingconsiderable internal, or possible external resistance, a-mostly of the forward-curved blade, or so-called mixed-flow centrifugal type. The latter is really a centrif-

39

ugal type with axial inlets, having a pressure curveresembling a backward-curved-blade centrifugal fan.Both types have the high capacities requisite for acompact unit.

62. Cooling tower fans are usually of the propellertype, but axial types are used for packed towers, andoccasionally a centrifugal fan is used on the forced-drafttower.

63. Circulating fans are invariably of propeller, ordisk type, and are made in a vast variety of blade shapesand arrangements. They are designed for a pleasingappearance as well as for efficiency.

64. We will discuss the maintenance of fans inChapter 5. Now let's move on to the motors used on thefloor-mounted unit.

65. Motors. Room air conditioner use motorsranging from 1/6 horsepower to 6 horsepower. Motorsin most cases are controlled directly by the systemcontrols, such as thermostats, timers, pressure switches,or other automatic devices. The most common voltageapplication is 115 or 230 volts.

66. The necessity for low current draw on a 115-voltcircuit also makes it necessary to use permanent-split-capacitor motors for the fans on room air conditioners.Shaded pole motors are used when current draw isn't aproblem.

67. The hermetic compressor design makes itimpossible and unnecessary to service compressor motors.Fan motors are accessible and you should service them asrecommended by the manufacturer's instructions.

68. Permanent-split-capacitor motors do not requirea starting switch, but the capacitor-start induction-run andthe capacitor-start capacitor-run motors use a startingswitch.

69. Motor protection is similar to that described inthe previous section. Most compressor motors and air-moving motors are equipped with thermal protectors.These may be hermetically sealed for installation withinthe compressor shell or open for mounting on the outsidecompressor shell. Hermetically sealed protectors providebetter protection where conditions such as loss of charge,obstructed suction line, or low ambient temperatures onstalled rotors can be troublesome.

70. When applying an electric motor, the followingcharacteristic are important:

a. Mechanical arrangement including the positionof motor and shaft.

b. Speed range.c. Horsepower.d. Torque.e. Inertia.

f. Frequency of operation.71. The torque required to operate the driven

machine (compressor) at every moment between initialstartup and eventual shutdown is an important factor indetermining the type of motor to be used.

72. The torque available at standstill, the startingtorque, is usually welt above the torque at rated full load.The starting torque may be less than I00 percent, or ashigh as 300 percent of full load torque.

73. The starting current is usually 400 to 600 percentof the current at full load.

74. Full-load speed also depends upon the design ofthe motor. For induction motors, a speed of 1725 r.p.m.is typical for 4-pole motors, and a speed of 3450 r.p.m.for 2-pole motors (60-cycle). Full-load torque is thetorque developed to produce the rated horsepower at therated speed. Motors have a maximum or breakdowntorque which cannot be exceeded without causing anabrupt change in speed. The relation between breakdowntorque and full-load torque varies with motor design.

75. The required horsepower also determines themotor rating. The horsepower delivered by a motor is aproduct of its torque and speed. Since a given motor willdeliver increasing horsepower up to a maximum torque, abasis for horsepower rating is needed. The NationalElectrical Manufacturers Association bases horsepowerrating upon breakdown torque limits. Full-load rating ofgeneral purpose open type motors is related to thewinding temperature rise, with a temperature rise limit of40° C. by thermometer and of 50° C. by resistance forClass A insulation. Higher temperature rises may beallowed for enclosed and special-purpose motors.

76. The service factor of a general purpose motor isdefined as "a multiplier which, applied to the normalhorsepower rating, indicates a permissible loading whichmay be carried under the conditions specified for theservice factor." Motors, other than general purposemotors, have a service factor of 1.0.

77. In this chapter the last subject we shall discuss isthat of drives.

78. Drives. The fans and compressor motors areusually direct drive. Fans over 30 inches in diameter arebelt driven to reduce the speed below that of the drivingmotor and to meet the sound level requirements.Housed fans in the smaller sizes (up to l0 inches) areeither direct driven or belt driven, in accordance withsound level and other application requirements. Larger-size housed fans are exclusively belt driven.

79. Adjustable pitch pulleys are usually provided topermit you to balance air delivery against systemresistance.

40

Review Exercises

NOTE: The following exercises are study aids. Write youranswer in pencil in the space provided after each exercise. Usethe blank pages to record other notes on the chapter content.Immediately check your answers with the key at the end of thetext. Do not submit your answers for grading.

1. Before you plug in an air-conditioning unit youshould read the _____________. (Sec. 11,Par. 5)

2. When proceeding to plug in an 155-volt air-conditioning unit you find that the receptacle isfor a two-prong plug and the A/C unit hat athree-prong plug. You cut off the round prongand make your connection. What conditionexists with the round prong removed? (Sec. 11,Pars. 9, 10, and 16)

3. Is it permissible to connect a 9.5-ampere ratedair conditioner to a 15-ampere circuit if otherequipment connected to the same circuit uses 4amperes? (Sec. 11, Par. 12)

4. You receive a work order to replace an air-conditioner compressor motor that has burnedout due to an overload. What other unit shouldyou replace? (Sec. 11, Pars. 24 and 25)

5. As the room air passes through the its heat isabsorbed by the refrigerant. (Sec. 11, Par. 28)

6. At what component of the air-conditioning unitis the temperature of the refrigerant gas raisedabove the outside air temperature? (Sec. 11, Par.29)

7. What three components of an air-conditioningunit will collect dir and thus restrict airflowthrough the unit? (Sec. 11, Par. 32)

8. Before you check a capacitor with an ohmmeteryou should __________________ thecapacitor. (Sec. 11, Par. 44)

9. During the process of troubleshooting aninoperative. compressor motor, you check theoverload protector with an ohmmeter. What isthe condition of the protector if. the meterindicates zero? (Sec. 11, Par. 46)

10. Does a low- or high-wattage draw indicate a lowrefrigerant charge? (Sec. II, Par. 51)

11. What are the two major causes of poorperformance of an air-conditioner? (Sec. 11,Par. 62)

12. What precaution should be observed whencleaning an air-conditioner condenser withsuperheated steam? (Sec. 12, Par. 7)

13. When mixing a liquid acid cleaning solutionshould you add the water to the acid or the acidto the water? (Sec. 12, Par. 12)

14. What will .result if the water bleed tube of theevaporative condenser should become clogged?(Sec. 12, Pars. 18 and 19)

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An air-conditioning compressor was written up because itwould not unload during light load conditions. Whatcould prevent the compressor from unloading? (Sec. 12,Pars. 31-39)

What part of the capacity control actuator regulates theoil pressure to the compressor cylinder unloadermechanisms? (Sec. 12, Par. 31)

What pressure in the cylinder unloader mechanism willhold the compressor suction valves open? (Sec. 12, Par.39)

18. Should the air-conditioning compressor beloaded or unloaded when adjusting the cylinderunloader system? (Sec. 12, Par. 41)

19. When you are preparing to install a solenoidvalve, what two things on the valve should youcheck? (Sec. 12, Par. 49)

20. You have been assigned the task of replacing asolenoid valve that has a burned out coil. Whatshould you check for before installing the newvalve? (Sec. 12, Par. 50)

21. What are the two methods of varying thevolume of air handled by an air-conditioningsystem? (Sec. 12, Par. 56)

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CHAPTER 5

Fresh Air and Air Duct System

YOU HAVE probably heard this statement many times:"This room is smoky." As an air-conditioning mechanicyou should be particularly interested. Why is the roomsmoky? Why can't the air-conditioning system handle thesmoke? What can you do to correct this situation?

2. These questions and many others you may comeupon will be answered in this chapter. Such subjects asdampers, fans, coils, and air duct systems are discussed.You will also learn how to determine duct sizes and howto balance a system.

13. Dampers1. Dampers of the following types are usually

installed in an air-conditioning system:a. Bypass damper (A of figure 21).b. Mixing damper (B of figure 21).c. Air intake damper (C of figure 21).d. Volume damper, as shown in figure 22.e. Recirculating damper (D of figure 21).2. Bypass dampers control and regulate the airflow

from return ducts and the intake openings. The air isdiverted in specific directions to avoid airflow through acertain duct area. Mixing dampers are usually installed atduct and intake openings to provide a mixture of air fromthe exterior and interior spaces to the air-conditioningequipment. Mixing dampers control and regulate theairflow from room areas and the fresh air intake. Thepurpose of a mixing damper is to mix these volumes ofair in the proper proportion. The volume damper isinstalled in the interior of the duct, as shown in figure22. It provides a division for air volume to the openingsby changing the area of the passageway. The volumedamper is generally constructed of one blade and isfastened to the side of the duct with indicating sectionson the exterior side of the duct surface for adjustments.

3. Intake dampers are installed at the openingconnections to the air-conditioned equipment. Thesedampers usually control and regulate the airflow from theduct system connecting the spaces served to theequipment. The recirculation damper and exhaustdamper are usually connected to a common motor by

linkage. The linkage is arranged so that when onedamper is open, the other damper is closed. Usually theycan be at any position, from fully open to fully closed.

4. Dampers are installed in numerous ways toregulate and control air movement. They may haveeither one or several blades and may have automatic ormanual controls.

5. Operation and Controls. All dampen operateeither manually or through the use of automatic controls.Automatically controlled dampers are generally used inlarge air-conditioning systems and are operated by amotor. The motor operates pneumatically or electrically,and moves the dampers to various positions. The size,material, methods of operation, leverage, location, andsigns of the motor vary with the manufacturer'sspecifications and installation requirements. Motorcontrol and operation was covered in the precedingchapter.

6. Manual damper control is done through the useof rope or cable extensions. They are generally used asexit or intake dampers located in remote locations orinaccessible places in the system.

7. Maintenance. A few defects that might occurin the operation of a damper or louver follow:

a. Bent shafts.b. Binding of blades or operating mechanism.c. Bent rods or levers.d. Air leakage.

The most common defect that causes erratic damperoperation is binding blades.

8. Wherever possible, you must inspect damperoperation; and if any of the above defects are found,immediate action must be taken to repair the unit.

9. Most large dampers are built as a single unit andconstricted with a frame to fit the duct and chamberopening. If the unit needs to be replaced, the completedamper unit can be taken out and a new damperinstalled. Whenever the services of a sheet metal workerare needed, the civil engineering section should benotified according to local procedures.

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Figure 21. Typical air-conditioning system.

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Figure 22. Volume damper.

10. You should refer to construction drawings andspecifications for location of dampers and installationdetails.

14. Fans1. Fans are used for circulation of air in duct

systems and are usually of one of the following types:a. Multiblade fans with blades curved backwards.b. Multiblade fans with blades curved forward.c. Multiblade fans with blades curved backward at

the tip and forward at the heel.d. Multiblade fans with radial blades.e. Propeller or disk type.2. The forward blade fan is a commonly used fan.

It operates at a relatively low tip speed for a givenpressure. It is compact in size and quiet in operation.The motor used with this type of fan should have agreater capacity than is actually needed by the fan.Forward blade fans do not operate well in parallel. Thebackward blade fan requires higher speeds for equivalentefficiency.

3. The propeller, or disk type fans are seldom usedin duct systems. They develop relatively low pressures.The propeller fan is used for moving large quantities ofair against low pressure with free exhaust.

4. The following information is required inselecting a fan for a given installation:

a. The number of c.f.m. of air to be moved.b. The static pressure required to move air through

the system.c. The motive power available.d. The operation of fans in parallel or singularlye. The degree of noise permissible.f. The nature of the load.5. Knowing the above information, you can refer

to the manufacturer's manuals to determine thespecifications of each size fan.

6. Figure 23 illustrates two different type fans thatmay be used in an air-conditioning system.

7. Supply and Booster Fans. Depending on theiruse in a duct system, a fan may be referred to as a supplyfan or a booster fan. If a fan is furnishing or supplying alarge volume of air, it is often referred to as a supply fan,its name being derived from the fact that it supplies theair. A booster fan is used in distributing air to a certainportion of the duct system. This fan helps in

Figure 23. Types of fans.

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Figure 24. Blower bearing.

moving a specific amount of air to a portion of thebuilding.

8. Maintenance. Once a year you shouldcompletely disassemble and inspect fans for defects.Bearings on fan shaft or motor are cleaned, checked forwear, and replaced if necessary. Ball bearings arerepacked with grease and sleeve bearings are lubricatedwith oil or grease as prescribed by the manufacturer.When handling fan wheels, you must be careful not tobend them. This will cause them to wobble. Rustedsurfaces should be cleaned and painted to reducecorrosion.

9. The blower wheel is inspected for properalignment and freedom of rotation. Bent vanes must berepaired. Axial clearance is checked to insure that thewheel is not binding on the scroll. The adjustment ismade by relocating the position of the shaft thrust collar,as shown in figure 24. Total axial movement of theshaft after final adjustment should be approximately 1/32inch. The thrust collar is locked in place with a thrustcollar set screw; worn thrust washers must be replaced.Periodic soakings of the washer in oil prolongs its life.The blower shaft sleeve bearings are normally lubricatedwith oil, while the ball bearings are packed with grease.Grease cups are generally refilled once a year, but should

be inspected frequently for lubricant. During periodicinspections, you may find the blower surfaces rusted.You must clean it and apply a coat of rust-resistive paint.

10. Fan noise may be caused by improper fanselection. The tip speed required for a certain capacityand pressure varies with the type of blade. You mustremember that a fan has a rated capacity and if itoperates beyond this, it will become noisy. Other factorsthat could cause noisy operation are loose or worn belts;improper construction of ducts and airways; and loose fanmountings.

15. Evaporator or Chilled Liquid Coil1. Chilled water coils are designed to conform to

all the specifications and to handle the necessary chilledwater that may be required by changing load conditionsin a building. The fin metal is generally made of copperor aluminum, as these metals readily conduct heat. Fintype construction gives more surface area. The plate-fincoil used for the refrigerant circulating system and thechilled water circulating system are similar, differing onlyin minor construction aspects; one system is filled withrefrigerant and the other with chilled water.

2. Operation and Controls. The duct type, plate-fin cooling coil is supplied with a coolant controlassembly, which is fitted with a drip pan and drain. Therelated duct thermostat bulb is fitted within the air inletduct. The coil tubing passes through plates or fins ofthin metal stacked six to the inch, the entire length ofthe coils. The airflow through the coil is parallel to thefins which may be curved slightly to create a turbulentflow of the air. Thus, all the air is caused to come incontact with the cooling surfaces. The coils arepreferably installed on the intake side of the recirculatingfan in the system so that the coil inlet face is alwaysopen and free for cleaning. Slight deviations in airquantity from the cooling ducts will materially alter theperformance of the system. The designated air quantitiesshould be limited to plus or minus 5 percent so that theproper operating speed for the circulating fan in the airducts is maintained.

3. Maintenance. In most installations, coolingunits are provided with filters in front of the coils toprevent the coil from becoming coated with foreignmaterials. These filters must be inspected and cleaned atfrequent intervals. Where filters are not provided, a linty,matlike accumulation will form at the intake side of coils.Too much of this accumulation would result in a markeddecrease of airflow over the coils. A film of dust,organic material, and grease will also form on the entirecooling surface, reducing the rate of heat transfer andcreating a source of objectionable

46

odors. Therefore, the coils should be inspectedfrequently and cleaned as often as necessary.

4. Cleaning. In cleaning coils, a regular check-offlist is generally followed for the entire air duct system.First, you must stop the fans, then open the coil accessplates. After this is done, brush the intake side of thecoil to loosen the lint and dirt. If this material is cakedon the fins, use the special combs with teeth spaced to fitbetween the fins. Wire brushes may be used if care istaken to avoid damage to the fins.

5. Leaks. Coils that develop leaks must berepaired immediately. Repairing a leak can develop into amajor job. It may require the coil to be drained so thatproper maintenance can be performed. Manufacturer'maintenance manuals generally give coil structuralmaterial and recommended procedures for repairing coils.

6. Replacement. Every air-conditioningInstallation has its own peculiarities as to design andinstallation; therefore it is impossible to give specificprocedures on coil replacement information relative toyour particular installation can probably be located in theconstructed prints and manufacturers specifications andhandbooks.

16. Brine and Heating Coils1. Brine coils are used in air-conditioning systems

that require low temperatures for dehumidificationpurposes. The brine (usually ethylene glycol) flowingthrough coils is designed to withstand low temperatures.Location of the brine coils for your installation can befound in construction drawings.

2. Operation and Controls. Brine coils operate onthe same basic principle as the chilled water coils exceptfor minor engineering differences. Refer to constructiondrawings and manufacturer's manuals and handbooks fordetailed information concerning operation and controls.

3. Maintenance. Maintenance for the brine coil isaccomplished in the same manner as maintenance onchilled water coils, as explained previously. Onemaintenance precaution that must be taken in repair orreplacement of the brine coil is the preservation of thebrine.

4. Heat Coils. Heating coils are used to heat theair pressure through coils for humidification purposes.These coils are supplied with hot water or steam. Hotwater coils should not be operated with final airtemperature below 50° F. Construction characteristic andlocation of the heating coils can be found in installationdrawings, manufacturer's manuals, and handbooks.

5. The operation, control, and maintenance ofheating coils are very similar in principle to that of thechilled water coils explained previously. Many heating

coils are controlled by an automatic temperature control;this control throttles the steam or water to the coils tohelp protect against subfreezing air coming into directcontact with the hot coil. This can become verydangerous and would result in damage to the equipment.A bypass damper control is used on hot water coils underthe above circumstances, which allows the maximumamount of water to flow into the coil.

6. Heating coils are constructed to withstand highpressures and may or may not be of the self-drainingtype, therefore provisions are made for draining in caseof repair or replacement.

17. Air Duct Systems1. The duct system is used to distribute

conditioned air from one location to another. Thissystem may cost 25 percent of the initial investment.The resistance of a duct system is a substantial portion ofthe static pressure against which the fan operates-animportant item in annual power cost. For this reason, inlarger installations economies can be realized by designingthe ducts to balance first cost against operating costrather than by using the rule-of-thumb methodssometimes permissible on smaller installations.

2. Pressure Losses. Along an ideal frictionlessduct system, total pressure-the sum of static and velocitypressures-remains constant in an actual system, lossesoccur due to two effects: friction losses and dynamiclosses. Friction losses are primarily from surface friction,while dynamic losses result from sudden changes invelocity or direction, or from other eddy sources. Mostof the pressure drop in a straight duct is caused bysurface friction. You will find that various equations areused to calculate losses. These formulas are slantedtoward design engineering. You will not be required tostudy them.

3. Duct Sizing. Ducts are sometimes sized byselecting a velocity at the fan discharge and by makingarbitrary reductions in velocity down the run, usually ateach branch or takeoff.

4. This method, called the velocity reductionmethod, has simplicity to recommend it, but it takes noaccount of the relative pressure losses in variousbranches. It use is acceptable only for estimating simplelayouts. The method is not recommended for actualdesign.

5. The following table presents maximum designvelocities considered good practice for conventionalsystems in various applications. Quality and size ofinstallation, power costs, space limitations, and noise arethe factors which should be considered in the selection ofthe proper velocity.

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RECOMMENDED MAXIMUM DUCT VELOCITIES, IN F.P.M.APPLICATION SUPPLY DUCT

Trunk and Small Rises ReturnLarge Rises and Mains

BranchesResidences 800 600 600Apartments and hotel

bedrooms 1,500 1,100 1,000Theaters 1,600 1,200 1,200Private offices-deluxe 1,100 800Private offices-average 1,300 1,000General offices 2,200 1,400 1,200Restaurants 1,800 1,400 1,200Shops-small 1,500 1,200Department stores-

lower floors 2.100 1,600 1,200Department stores-

upper floors 1,800 1,400 1,2006. High-Velocity and High-Pressure Air

Distribution. In recent years there has been a trendtoward higher duct velocities to reduce duct size at theexpense of increased friction. Any system with velocitiesgreater than 2,000 f.p.m. is usually considered to be ahigh-velocity system. Because of the higher average staticpressure (5 to 10 in. w.g. at the fan), these systems arefrequently called high-pressure systems.

7. In these systems, relatively high duct pressuresare necessary to obtain stable control of variable volumeoutlets, or to obtain the required velocity for highinduction terminal units. Increased stability is inherent inoutlets with high design pressure drops (1/2 in w.g. orgreater), since a given change in duct static pressure, dueto throttling of a portion of the outlets, has a decreasingeffect on the airflow through the remaining outlets as thedesign pressure drop increases. For example, a duct staticpressure increase of 0.20 in. w.g. will increase theairflow through an outlet designed for a 0.20-in. drop by41 percent, but by only 10 percent through one designedfor a 1.0-in. drop.

8. When high outlet discharge velocities are used,high-temperature differentials between room and supplyair may be employed, since induction within the roomwill afford adequate mixing of the supply stream before itenters the occupied zone. For example, a 30° F.difference may be used instead of the 20° F. differentialcommon to conventional systems, with a one-thirdreduction in the supply-air volume. Some systemsemploy high velocity in the main ducts, with sound-attenuation boxes where the velocity is reduced.

9. The space saved as a result of using highvelocities should be balanced against increased first andoperating costs. It is necessary to use fans of heavierconstruction for the higher static pressures. Great care isneeded in the construction of duct work to prevent

leakage, and it is common practice to seal all joint andseams with sealing compound, tape, or by welding orsoldering. Round duct is preferred to rectangular becauseof its greater rigidity, which allows the use of lightergauges and avoids the need for reinforcing members.Spiral conduit, made from 2 1/2- to 6-in. zinc-coatedsteel or aluminum strip spirally wound with a double-locked seam, is light, tight, and strong. Particular careshould be given to the selection of fittings to avoidexcessive pressure drops and noise generation. Avoidusing 90° fittings, or fittings that are sleeved into theinside diameter of the main duct. The problem ofmaintaining satisfactory sound levels is magnified, andoutlets with a low level of noise generation and a highdegree of sound attenuation are required. The highersound level of a high-pressure fan ordinarily requires theuse of a sound absorber immediately downstream. Linedduct may be used where space permits; otherwise abaffle, cell, or plenum type absorber is required. Specialattention should be given to the design of fan isolationand the use of flexible connections.

10. It is good practice to examine the critical(maximum pressure drop) run of conduit afterpreliminary sizing is completed and to reduce velocity atselected points if a significant reduction in fanhorsepower can be effected. Sometimes the use of morecostly special fittings of low dynamic loss can be justifiedfor such runs. Conversely, where excess static pressure isto be dissipated in shorter runs, it may be desirable tosize certain portion for higher velocities.

11. Duct Materials. The composition of ordinarygalvanized-steel sheets includes approximately 0.10percent carbon, 0.40 percent manganese, and minutequantities of phosphorus, sulphur, and silicon, with aheavy zinc coating. Of somewhat superior resistance toatmospheric corrosion (where high moisture conditionsare encountered) is galvanized copper-bearing steel with acopper content of about 0.20 to 0.30 percent. Aluminumduct should be fabricated from 2S or 3S 1/2 or 3/4 hardstock; 3S is preferred for larger ducts.

12. Exhaust ducts for chemical laboratories andother applications involving corrosive fumes use copper,stainless steel, monel metal, lead-coated, or lead itselfwhen necessary. Intake and exhaust hoods are frequentlymade of copper although this refinement is necessarywhen galvanized-steel construction is accessible forinspection and painting. Materials other than metal maybe used in ducts for reasons of appearance or cost.

13. Board material. Such materials are cut to desiredsize and fastened by various means, with corner trim oredges and band trim along the seams. Most materials inuse include in-

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sulation value as a property. Besides filling therequirements for any ducts, the material should befireproof, verminproof, moldproof, free from odor, andnot subject to deterioration from water or vaporpenetration.

14. Prefabricated materials. These ducts and fittingsare available in standard even-inch dimensions in thesmaller sizes and are designed primarily for the residentialand small commercial market. They must meetstandards similar to those specified for the boardmaterials.

15. Sheet-Metal Standards. Ducts and sheet-metalconnections may be fabricated according to severalmethods of construction. It is not too important whichmethod we use, but the construction must meet thefollowing standards:

a. Materials of suitable quality for the purpose.b. Proper gauge for strength.c. Cross breaking and reinforcement, where

needed, for rigidity and freedom from mechanical noiseinduced by vibration.

d. Tightness of seams and corners to minimizeleakage.

e. Freedom from sharp internal edges to avoidnoise regeneration.

f. Conformance with design standards to permitdesired airflow.

16. To insure desired airflow without excessivefrictional and dynamic losses design standards areessential to govern the fabrication of shapes, fittings,vanes, and connections to equipment. Nearly all of thesestandards are based on two fundamentals of airflow:

a. Air flowing from the chamber or conveyor ofsmaller section area into one of larger area tends tocontinue in a straight line. Air will not diverge, unlesschanged by vanes, at an included angle greater than about20°.

b. Air flowing from a chamber or conveyor oflarger section area into one of smaller area tends toconverge uniformly and follows the laws of entrance toorifices in fluid flow.

17. Duct Heat Gains and Losses. Whenever theair inside the duct is at a temperature different from theambient temperature, heat will be transmitted outwardlyor inwardly. The gain or loss, if of appreciablemagnitude, may be important because:

a. Transmission to or from a space not beingtreated, but through which the duct passes, is a total lossof heating or cooling effect.

b. Transmission to or from the same space beingconditioned may put too large a part of the heating orcooling effect where it is not wanted. The correction inthe first case is either insulation (or dead air space) or agreater investment in heating or cooling capacity, or both.

The correction in the second case is a redistribution ofthe air to the various supply grilles to compensate for thecooling or heating effect of the duct surface.

18. Heat Insulation. Insulation is employed for tworeasons: (a) to reduce loss of heating or cooling effect or(b) to prevent sweating of the duct. Determination ofthe first effect is computed by use of the followingequations:

Q = UA (t1 – t0.)where Q = heat loss (B.t.u./hr)

U = B.t.u./(hr)(sq ft.)(°F. diff.) average valuesvalues

A = duct surface (sq. ft.)t1 = air temperature inside duct (°F.)t0 = air temperature outside duct (°F.)

19. The economic value of insulation depends uponthe total annual cost of the heating or cooling effectsaved. A precise answer can be obtained only by a studyof the particular application.

20. Sweating occurs when the temperature of theduct surface is below the dewpoint of the air touching it.For bare-sheet-metal duct:f0 (t0 – t3) = U (t0 – t1)

t3 = t0 - U (t 0 – t 1)1.6

where t3 = duct surface temperature (°F.)U = overall transmission coefficientf0 = surface conductance of outside duct

surface21. Air Leakage and Duct Maintenance. Air

leakage varies over wide limits, depending on air pressure,type of construction, and workmanship, principally thelast. Actual tests on typical supply systems have shownleakages from 5 to 30 percent. Corner holes normallyaccount for only a small portion.

22. The largest source is at transverse seams locatedagainst the wall or ceiling in such manner that tight jointsare almost impossible. Allowance should be made forleakage, depending on job conditions. For supply systemswith static pressure in excess of 1 inch w.g., calking,felting, or soldering is recommended.

23. Ventilating and air-conditioning ducts normallyrequire little maintenance. When they are dry thedeterioration by corrosion is usually negligible. Periodiccleaning is important because even with comparativelyefficient air-cleaning devices, dirt accumulates over aperiod of time. A shift in dampers will frequently blow acloud of dirt into the room. More important is the realfire hazard of such an accumulation, which has beenrecognized by the Fire Underwriters. Ducts should beprovided with access doors to allow for cleaning.

24. System Balancing. With the fan in operation,adjust the damper op the air-intake trunk until thevelometer shows an air intake equal to

49

one-half the dwelling's cubic volume per hour. After youhave done this, you must lock the damper in place.

25. A formula for calculating air quantities requiredfor sensible cooling load is:

Quantity of air (c. f. m.)= sensible heat load (B.t.u./hr.)

1.08 X temperature change

26. Temperature change is the difference (°F.)between the room temperature and the temperature ofthe entering air. Another rule of thumb that you mayuse to estimate the quantity of cooling air required is tofigure on eight air changes per hour in the area to beconditioned.

Quantity of air (c.f.m.) = 8 X room volume (cu. ft.)60 min. /hr.

27. You should not use this rule if the risers aresmaller than standard (3 1/4" x 14") or if the branchducts are less than the equivalent of an 8-inch roundduct. Another exception is when unusually largeamounts of glass or exposed wall are present.

28. At all T-type duct transitions, check the firstgrille downstream from each branch with all of the grillefrets or louvers in straight-flow position. Adjust thebranch dampers until the velometer registers equalvelocity through the grilles on both trunks. After youhave equalized the velocities, you must lock the dampersin position. Continue this procedure along the ductsystem to any addition T-type transitions until all the T-type transition dampers are adjusted.

29. If splitter dampers are installed, follow the sameprocedure until approximately the same air velocity overthe entire duct and grille system has been reached.

30. Proper quantity of return air. After you know thetotal quantity of air required for cooling the conditionedarea, you must adjust the air-conditioner blower drive fordelivery of the design airflow. Check the delivery asclose to the fan outlet as possible. The air velocity timesthe total outlet area will determine the total air volumebeing circulated. For example:

80 f.p.m. X 8 sq. ft. = 640 c.f.m. being circulated31. Once the airflow is adjusted to the desired cubic

feet of air per minute, you will have to tighten the nutson the fan sheave for permanent adjustment of airflow.At this time you should check the current the blowermotor is drawing to b certain that it is capable of drivingthe fan without overloading and burning out.

32. You must be sure that the return-air grille islarge enough to handle all the air supplied to the space.Any lack of return air can seriously affect systemoperation.

33. Balancing air discharge grilles. High-side-wall,double-deflection supply-air grilles predominantly used inaverage sized systems will be discussed first. You mustuse the design data to find the amount of air required foreach room or area. The grilles are usually dampered.Equalize and properly deflect the air delivery to thevarious areas by adjusting the louvers or grille frets.

34. Starting with the grilles closest to the blower,adjust the front horizontal grille frets so that you achievethe proper blow and drop. Blow and drop will bediscussed later in this volume. A lighted match, warmthermometer, or rubbing alcohol on the exposed surfaceof your arm will help you to determine just howaccurately the desired vertical flow of air is beingachieved. Constant association with airflow will enableyou to tell just what the air deflection is doing by thesensation of the airflow over your body. By adjusting therear frets of the grille, the horizontal width of the airpattern is established. The ultimate goal is to achieve aneven air pattern about 5 ½ to 6 feet above the floorlevel over the greatest amount of room area whileattaining as close as possible the cubic feet of air requiredfor the particular room. Then continue to the nextclosest grille to the supply blower, and so on to the lastgrille. It is possible that proper airflow from distantgrilles cannot be attained. It is then necessary to returnto the grilles closest to the blower outlet and partiallyclose some of their rear frets, thereby forcing more air tothe distant parts of the system. Continue the adjustmentof rear grille frets in the same sequence until there isample air supply to all rooms. 35. In checking the airvolume from the grille, play the recording air-measuringinstrument over several locations on the grilles andaverage the readings for final tabulation of total airflow.In setting the supply-air delivery patterns, refrain fromprojecting supply air directly toward a return grille.

36. The ceiling diffuser must be adjusted to patternthe airflow over most of the ceiling area. The diffuserusually has adjustable rings, dampers, or diffusing gridswhich will do the same thing as a high-side-wall grillewhen it is adjusted for patterning air delivery to theconditioned area.

37. The flush-floor diffuser with bars or frets isadjusted to pattern air sweep in an arc toward the ceiling.This will blanket the conditioned area just as high-side-wall grille does.

38. The baseboard type of diffuser has a balancingdamper for controlling airflow. This diffuser does a goodjob, even though it has a minimum of adjustments thatyou can use for balancing.

39. The low-side-wall diffuser has grids, vanes, orfrets for producing air patterns. It can produce anexcellent cooling or heating condition when the

50

air is deflected properly. You will encounter fewproblems with high-side-wall or ceiling diffusers. Careshould be taken with the other types of diffusers,especially in relation to obstruction which interfere withthe required air pattern. Such devices must be balanceddifferently for summer and winter conditions.

Review Exercises

NOTE: The following exercises are study aids. Write youranswer in pencil in the space provided after each exercise. Usethe blank pages to record other notes on the chapter content.Immediately check your answers with the key at the end of thetest. Do not submit your answers for grading.

1. What type of dampers regulate airflow fromreturn ducts? (Sec. 13, Par. 2)

2. The damper in a duct is operating erratically.What is the most probable cause? (Sec. 13, Par.7)

3. Which type of fan is most commonly used in aduct system? (Sec. 14, Par. 2)

4. What type of fan would you install in an areawhere large amounts of air are to be exhausted?(Sec. 14, Par. 3)

5. How is the axial clearance adjusted on a blowerwheel? (Sec. 14, Par. 9)

6. Why are the fins a cooling coil made ofaluminum-or copper? (Sec. 15, Par. 1)

7. How many fins would a 2-foot coil contain?(Sec. 15, Par. 2)

8. How would you straighten the fins on a coil?(Sec. 15, Par. 4)

9. Why is a brine solution used as a coolant in anair-conditioning system? (Sec. 16, Par. 1)

10. Which type of pressure loss is caused by anelbow in the duct? (Sec. 17, Par. 2)

11. Why isn't the velocity reduction method usedfor sizing duct for complex systems? (Sec. 17,Par. 4)

12. A system with a velocity rating of 2400 f.p.m. isconsidered a ______________ system. (Sec.17, Par. 6)

13. How are duct joints sealed? (Sec. 17, Par. 9)

14. What type of material would you construct aduct with if corrosive fumes are to be handled?(Sec; 17, Par. 12)

15. What occurs when air flows from a smallchamber to a large area? (Sec. 17, Par. 16)

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16. What is the loss of cooling effect of a 12-squarefoot duct with a temperature differential of 10°and a U-factor of 1.14? (Sec. 17, Par. 18)

17. Where does most duct air leakage occur? (Sec.17, Par. 22)

18. How much air is required when the sensibleheat load is 49,000 B.t.u./hr. and a temperaturechange is 15°? (Sec. 17, Par. 25)

19. How can you determine the vertical flow of airfrom a grille? (Sec. 17, Pa. 34)

20. The horizontal airflow pattern is controlled bythe ______________ ______________ ofthe grille. (Sec. 17, Par. 34)

21. Which type of diffuser is the hardest to use forbalancing? (Sec. 17, Par. 38)

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CHAPTER 6

Controls

YOUR BRAIN is a control system. It controls yourmovements and it responds to various situations. Haveyou ever touched something hot? You really let go of itfast, didn't you? The control system of an airconditioner acts like a brain. It senses a change andresponds with a corrective action.

Three types of control systems will be discussed.These are motor, electric, and pneumatic controls.Responsive devices sensitive to temperature, pressure, andhumidity will also be studied.

18. Responsive Devices1. Most automatic controls function because they

are responsive to changes in temperature, pressure, andhumidity. We will discuss the various responsive devicesthat you will encounter in your control system.

2. Temperature-Responsive Devices. Many ofthe automatic control units such as the thermostat, fanswitch, etc., must be responsive to temperature changes.The temperature change actually makes and breakselectrical contact within each unit.

Figure 25. Bimetal strip.

This action is an indicating signal transmitted to theprimary control for specific action such as starting orstopping the operation of a piece of refrigerationequipment.

3. Bimetal strip. To accomplish the above specificaction, the automatic control unit may be equipped with abimetallic strip. This strip is made by welding togethertwo pieces of dissimilar metals such as brass and "Invar,"as illustrated in figure 25. At a certain predeterminedtemperature, this strip does not deflect or bend.However, when the strip is heated, it will tend to bend inthe direction of the metal which has the least amount ofexpansion, as shown in figure 26.

4. By welding two electrical connections andcontacts to the arrangement shown in figure 27, anelectrical switch is constructed. This switch can be usedto control an electrical circuit responding to temperaturechanges.

5. The bimetal strip is the basic principle ofoperation of many of the temperature responsiveautomatic units. However, some units may be operatedby a bimetallic strip in the form of a

Figure 26. Bimetal strip being heated.

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Figure 27. A bimetallic switch.

spiral, a U-shape, a Q-shape, or even a helix, as shown inthe illustrations in figure 28.

6. Vapor-tension device. Another very common typeof temperature-responsive device is one in which theeffects of the temperature changes are transmitted intomotion by a highly volatile liquid. The most commonlyused vapor-tension device of this type is a simple

compressed bellows, shown in figure 29. It is made ofbrass and partially filled with alcohol, ether, or someother highly volatile liquid not corrosive to brass. Whenthe temperature around the bellows increases, the heatgasifies the liquid, causing the bellows to extend andclose a set of electrical contacts, as shown in figure 30.When the bellows cool, they contract and open theelectrical contacts. This vapor-tension principle also isused to operate some of the automatic control units.

7. Remote-bulb device. Not all the liquid-filleddevices are limited to just a simple bellows as describedabove. There are remote-bulb type devices that not onlyhave bellows but also have a capillary tube and a liquid orgas-filled bulb, as shown in figure 31. When the liquid orgas in the bulb is heated, part of the liquid gasifies or thegas expands and forces its way through the capillary tubeinto the bellows. The increase of pressure inside thebellows causes the bellows to extend and close a set ofelectrical contacts. When the bulb cools, the gasliquefies, causing a decrease of pressure in the bellows.This causes the bellows to contract and open the set ofelectrical contacts.

8. Pressure-Responsive Devices. Pressure-responsive devices are incorporated in refrigeration andair-conditioning systems to operate and regulate valves,controllers, operators, etc.

Figure 28. Various shapes of bimetal strips.

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Figure 29. Bellows contracted when cooled.

9. Bellows. One type of pressure-responsive deviceuses the action of a bellows in a similar way to theremote-bulb device mentioned previously. In this casethe bellows extends and contracts in response to thechanges in pressure. The action caused by the movementof the bellows opens and closes a set of electricalcontacts.

10. Bourdon tube. Another pressure-responsivedevice used in a pressure gauge is illustrated in figure 32.In this unit the pressure acts inside a hollow, flattened,bent tube called a Bourdon spring tube. The pressureinside the tube tends to straighten it, moving themechanism which turns the pointer. The pressure gaugemeasures pressures in pounds per square inch.

11. Humidity Responsive Devices. Humidity-responsive devices e regularly used to cause the openingor closing of solenoid or motorized valves which, in turn,control the flow of water or steam to the humidifyingequipment.

Figure 30. Bellows extended when heated.

Figure 31. Remote bulb device.

12. Humidity-responsive devices are designed withsensing elements which am very sensitive to humiditychanges. Usually these sensing devices activate the actionof a switch. A typical humidity-responsive device isshown in figure 33. The sensing element in this device isa number of human hairs which lengthen when thehumidity is high and shorten when the humidity is low.The lengthening and shortening action of the hairsmoves the lever, which. in turn opens and closes thecontact points to a humidifying unit.

19. Motor Controls1. A motor control is similar to a switch installed

in a motor circuit that opens and closes the power lead tothe motor. The major difference is that the motorcontrol acts automatically in response to temperature orpressure changes.

2. Function of Motor Controls. The function ofany motor control is to maintain a relatively constanttemperature within the refrigerated space.

Figure 32. A pressure gauge showing the Bourdon tube.

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Figure 33. A humidity responsive device.

This may be done by starting the unit when thetemperature rises and stopping it when the temperaturereaches its set point (control is satisfied). Thetemperature is constantly rising and failing betweenpredetermined set points (cut-in and cut-out).

3. Low-Pressure Motor Control. We can controlthe temperature of a refrigerated space through low sidepressure. If we control low side pressure, we ultimatelycontrol the temperature of the refrigerant in theevaporator. A pressure-temperature relationship chart isneeded for the following example. Our system containsR-12, and the desired space temperature is 40° F. Now,using the chart, we find that we must control the lowside pressure at 37 p.s.i.g. Therefore, we have controlledtemperature by pressure.

4. A bellows, diaphragm, or Bourdon tube is usedto motivate the points in the low pressure control (LPC).

5. The differential, cut-out minus cut-in, is set byregulating the amount of force exerted upon the bar bythe adjusting spring. There are many variations in thecharacteristics of individual types of motor controls.Each control has an adjustment of one kind or another.This allows the control a wide range of applications.

6. One of the more useful tools in controladjustment is the pressure control setting chart. Thesettings for most applications can be found by referringto this chart.

7. If the particular application desired is not foundon this chart, the next approach to use is the pressure-temperature relationship chart.

8. Assume that the desired cut-in pressure is 25p.s.i.g. and that the cut-out pressure is 10 p.s.i.g. Thedifferential would be 15 p.s.i.g. Since most controls haveonly two setting. to make, cut-in and differential, wefind that knowing the cut-out pressure is an importantfactor.

9. The two scales (one for cut-in and the other fordifferential) are located on the front of the control. Theadjusting screws are located on top of the control. Theadjusting screws are turned until the pointers indicate thepressures desired. Make sure that you read the scalesvery carefully. The unit should be allowed to cycle once.The cycling ON should take pace when the low sidepressure is 25 p.s.i.g., and the OFF cycle should occur

when the pressure drops to 10 p.s.i.g. These pressuresmay be observed on a gauge installed in the suction line.

10. Thermostatic Motor Control. The thermostaticmotor control (TMC) operates on temperature ratherthan on pressure. These motor controls can be used onmost types of refrigeration and air-conditioning units.They must be used on all units that utilize high or lowside floats and capillary tube refrigerant control devices.

11. Principles of operation. The operating principle ofthe thermostatic motor control is based on a physics lawwhich states that matter will expand when heated andcontract when cooled. The power element uses this lawin its function.

12. The element is a sealed container filled with aliquid, gas, or combination of the two. Any change intemperature surrounding the element will cause a pressurechange within the element. The power element consistsof three parts-a feeler bulb, capillary tube, and bellows.Any leak in the power element will render it useless.

13. The feeler bulb of the power element is locatedin suck a position as to be sensitive to any change in thetemperature of the controlled space. For domestic unitsthis location is right on the evaporator so as to controlthe evaporator temperature. It might also be fastenedinside the refrigerated space.

14. Any rise in temperature will heat the bulb,causing the charge to expand. This expansion will betransmitted through the capillary tube to the bellows,causing the bellows to expand. Attached to the bellowsand inserted into the housing to rest against one end ofthe lever system is a short push rod. The pressure of thepower element will expand the bellows, pushing the rodagainst the lever. This lever will cause other levers tomove, and the net result will be a set of electrical contactpoints closing. Closing of the points will cause the motorto start, and the unit will be in operation.

15. As the temperature at the feeler bulb drops, sowill the temperature of the bulb. This causes a drop inpower element pressure and will reduce the "push" onthe lever system. Part of the lever system consists of aspring which counteracts the power element pressure. Asthe element pressure drops, the spring will pull the pointsapart and stop the unit.

16. When you turn the adjusting knob clockwise,the spring will become compressed, causing the cut-intemperature to rise. Compressing the spring puts morepressure in opposition to the power element and demandsthat the element heat up even more to overcome thisincreased pressure, closing the points. The converse(turning the knob counterclockwise) will decrease springtension and lower the cut-in point

17. The TMC has a second spring that works inconjunction with the power element instead of

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against it. This spring is used to set the "cut-out"temperature (on some controls) or the differential (onother type controls).

18. Location of feeler bulb. Normally, the feeler bulbwill be tightly clamped to the evaporator. The TMC willoperate on the evaporator temperature. The bulb can belocated elsewhere if the situation demands it; some bulbswill be located in the cold box rather than on theevaporator. In this case the TMC will operate on thecold box temperature. On ice-making machines thefeeler bulb should be located in the ice bin. In thisapplication the TMC will shut the unit off when the icelevel reaches the feeler bulb and cools it. When the icelevel falls below the bulb, the bulb will warm up and turnthe unit on. If the refrigerated space has forced aircirculation, the TMC bulb should be mounted in thereturn airstream.

19. Replacement. The control mechanism is sodelicately built that it is impractical to repair in the field.If operation is erratic because of power element failure,mechanical (lever) action failure, or contact point failure,you should replace the entire switch.

20. Checking thermostatic motor controls.Thermostatic motor controls are very delicateinstruments. However, if they are not misused, they willgive years of trouble free service. Thermostatic motorcontrols are subject to several troubles, each of whichusually requires replacement of the complete control.Some of the more common troubles are treated in thefollowing paragraphs.

a. Loss of Charge. Occasionally the power elementwill lose part or all of its charge. This charge is verysmall and any loss at all will cause the unit to fail. Akinked or clogged capillary tube will give the sameindication as a loss of charge. Usually a power elementfailure requires replacement of the complete control.However, it is possible to get replacement power elementsfor some controls, although care must be taken to insurethat you have the correct replacement item.

b. Burned Contacts. Even though there is snapaction when the points open and close, they will burn. Insuch cases the points will either stick closed or becomepitted and never close. In some cases the point can befiled and the control will operate satisfactorily for aperiod of time. Filing the points should be considered atemporary repair and the control should be replaced assoon as possible.

c. Wear. The parts of a TMC are light and do notmove very far, but they do move many, many times eachday. One should not become too concerned about wearunless the unit has been in use a long time. However,

the TMC will wear out; when it does, remove andreplace it.

d. Electrical. Low and high voltages, high currentflow, frayed insulation, bad electrical contacts, andvarious other electrical malfunctions will cause the TMCto fail. Electrical troubles can often be determined andrepaired without having to replace the control.

20. Electric Controls1. There are many devices that may be used in

single- or three-phase circuits. We will cover each ofthese devices and how they operate.

2. Switches. The two types of switches used inelectric controls are the snap action and mercury. Theseswitches help. to reduce the problem of arcing when acircuit is open or closed.

3. Relays. There are many types of relays used inelectrical application. The type that we are interested inis the control relay. These are relays that open or closean electric circuit of higher voltage by the use of lowervoltage. These relays might be defined as an electricallyoperated switch. The main use of this relay is toremotely control an electrical device such as a fan motoror pump.

4. Control Transformers. A control transformersteps voltage down to operate different kinds of electricalcontrols. Line voltage applies to wiring or devices using110 or 220 volts. In control terminology, low-voltagecontrol takes in all controls and controlled devices thatuse 25 volts or less.

5. Magnetic Starter. Three-phase motors musthave at least two of the leads open to stop theiroperation. The device that opens these wires (circuit) is aline starter or magnetic starter. A magnetic starter isnothing more than a larger control relay which electricallyoperates two or more switch contacts.

6. Trouble Analysis. Before you can effectivelytroubleshoot a control circuit or system, you should knowthe circuit and how it operates. You can study the circuitin a wiring diagram of that particular circuit. Studyingthe diagram will give you a knowledge of the circuit as itshould normally operate. If the system does not functionproperly, the circuit is defective and an analysis of thetrouble and its location must be made.

7. Types of trouble. In practically all defectivecircuits, one .of the following types of trouble will exist:

a. Open-A circuit that has a break in any part ofthe circuit between the load and source.

b. Short-A circuit in which a conductor comes incontact with a point or object that it is not supposed totouch.

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(1) Direct short-A circuit in which one of thehot conductors comes in contact with a neutralconductor. This type of short circuit will "blow" a fuseor trip a breaker because there isn't any resistance in thecircuit.

(2) Cross short-A circuit in which two of thehot conductors make contact. This short will cause anelectrical feedback even though one of the conductors isopen.

c. Low power-This trouble causes units to operateimproperly. Two effects are sluggish motors and dimlights. Low voltage may be caused by loose, dirty, orcorroded connections as well as a low power source.

8. Location of trouble. As soon as you have studiedthe wiring diagram, the next step is to check out thecircuits with the appropriate test equipment.

9. Opens may be checked with a voltmeter or by acontinuity Lest. The continuity of a circuit may bechecked by a continuity meter or light, an ohmmeter, ora bell. The power must be off when making continuitytests. An ohmmeter will indicate infinity across an opencircuit, while the light or bell would not function.

10. A short can be located with an ohmmeter or bya continuity test. When checking a circuit with anohmmeter, a zero-resistance reading indicates a short, andan infinity reading indicates an open. Remember, whenusing an ohmmeter to test a circuit, the circuit powersource must be off.

11. Major Advantages of Electrical Controls.Electrical energy is commonly used to transmit thechange in space condition sensed by the controller toother components of the system. This signal from thecontroller will translate into work at the final controlelement. For this purpose, electricity has the followingmajor advantages:

a. Electric controls are available wherever there is asource of power.

b. Electric wiring is usually easy to install.c. Electric power readily amplifies the relatively

feeble impulse received from the sensing element.d. The impulse received from the sensing element

can be applied directly to produce one or severalcombinations or sequences in electrical output. Thisallows one actuator to perform several desired functions.

e. It readily permits remote control. The controllercan be a considerable distance from the controlled spaceor element.

12. Modes of Electric Controls. All controlsystems do not use the same types of action toaccomplish their purposes. The method by which acontrol system acts is called the control mode. We will

discuss the two-position, proportional position, andfloating controls.

13. Two-position control. In two-position controls thefinal control element occupies one of two possiblepositions (open or closed). The following is a list ofsystems that can use two-position control operation.

a. Domestic heating systems. (You may be calledupon to calibrate and troubleshoot controls used onheating systems.)

b. Electric motors on unit heaters and refrigerationmachines.

c. Water sprays for humidification.d. Electric strip heaters.

14. There are two values of the controlled variablewhich determine the position of the final controlelement. Between these values there is a zone in whichthe controller cannot initiate an action of the finalcontrol element. This zone is called the differential gap.As the controlled variable reaches the higher of the twovalues, the final control element assumes one of its twopositions, which corresponds to the demands of thecontroller, and remains there until the controlled variabledrops back to the lower value. The final control elementthen travels to the other position as rapidly as possibleand remains there until the controlled variable againreaches the upper limit.

15. There are two varieties of two-position controlwhich have been developed. The first, and oldest, maybe called simple two-position control. This has beenmore or less standard in the past and, as its name implies,it is fairly elementary. The second, which may be calledtimed two-position control, is a later development whichis rapidly replacing simple two-position control.

16. In simple two-position control, the controllerand the final control element interact in the mannerpreviously described without modification from anysource, either mechanical or thermal. The result iscyclical operation of the equipment under control. Thecontrolled variable fluctuates back and forth between twovalues determined by the magnitude of the differentialand the lag in the system. Since the action of thecontroller is such that it cannot change the position ofthe final control element until the controlled variablereaches one or the other of the two limits of thedifferential, these limits become the minimum possibleswing of the controlled variable.

17. In simple two-position control, the controllernever catches up with the controlled condition. Thus itcorrects a condition that has already passed, rather thanone which is taking place or is about to take place.Consequently, simple two-position control is applicableonly to systems in which total system lag (including notonly transfer lags but also measuring and final control

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element lags) is small. For this reason, simple two-position control rarely finds application in comfortheating control, but lends itself to the control of certainindustrial processes and auxiliary processes in airconditioning.

18. There is no single control point in simple two-position control. Rather, the controlled variable cyclesback and forth between two extremes. It is convenientto think of the control point as being midway betweenthe two extremes and offset as being a sustaineddeviation of this control point. Thus, offset is a shiftingof the whole curve either up or down, and the meanvalue is either raised or lowered so that it no longercorresponds to a point midway between the upper andlower limits of the controller differential.

19. Offset (on a temperature control system, forexample) is caused by the fact that the average value ofthe controlled variable must be lower under heavy loadconditions and higher under fight load conditions inorder that heat can be supplied at the lower or higher rateneeded. At peak load the burner must remain on 100percent of the time. Therefore the controlled variablecannot rise to the upper limit of the thermostatdifferential; otherwise the burner would be shut off.Likewise, under minimum load the controlled variablecannot fall to the lower limit of the differential or theburner would be turned on.

20. Since the amount of offset is limited in this wayby the differential, it is usually a serious problem insimple two-position control unless it happens that a widedifferential must be used.

21. The ideal method of heating any space is toreplace lost heat in exactly the amount needed. Withtwo-position control, this is obviously impossible since theburner is either "full-ON" and the heat delivered at anyspecific instant is either too much or too little. However,a close approximation of the ideal method .of heatdelivery can be had by using timed two-position control.In this method of control, heat is delivered in measuredquantities on a "percentage ON-time basis" so thatfluctuations of the control point are, for all practicalpurposes, eliminated.

22. For example, suppose we have a domesticheating system with a two-position control which isrequired to make up a heat loss of 20,000 B.t.u. in 1 hourat a certain load. The total capacity of the burner is40,000 B.t.u. per hour. This means that the burner willhave to operate 30 minutes out of the hour, whether it ison for 30 minutes and off for 30 minutes, on for two 15-minute periods and off for two 15-minute periods, on forsix 5-minute periods and off for six 5-minute periods, orany other combination in the same ratio.

23. In many cases the longer cycles would beunsatisfactory because the variations in temperature

would be too great. Dividing the heat into the correctlysized packages, so to speak, and delivering them at theright time gives a closer approximation of the desiredresult.

24. In timed two-position control, the basicinteraction between the controller and the final controlelement is the same as for simple two-position control.However, the controller responds to gradual changes inthe average value of the controlled variable rather thancyclical fluctuations. The gradual changes modify thetiming action to meet the changes in load.

25. Timing action may be provided mechanically,for example, by a cam mechanism. The chiefdisadvantage of this method is that only the relativeduration of the ON and OFF periods may be varied withchanges in load. The frequency remains fixed.

26. Thermal timing devices are more convenientand flexible. Placing side-by-side a heating element and atemperature-sensitive element controlling the powersupply to the heating element creates a thermal timer.As long as the ambient temperature is within certainlimits, the thermal timer will cool on its ON point,energize the heater, heat to its OFF point and deenergizethe heater, again cool to its ON point, and repeat thecycle. As the ambient temperatures decline, the timerequired for the timer to heat to the OFF point increases,and the cooling time decreases. Thus the timerautomatically changes the ratio of ON to OFF time.Moreover, the nonlinear shape of the heating and coolingcurves may be utilized to vary the total cycle time also,and therefore the frequency of the cycles.

27. In the latest models of domestic heatingthermostats, this principle is utilized by taking fulladvantage of the effect produced by the artificial heaterlong included as standard in similar thermostats. TheON and OFF points of the thermostat are fixed byadjustment of the setting dial, and a small offset in roomtemperature is allowed to measure changes in heatingload so as to vary the timing pattern of the thermostat.

28. In the two-position "weatherstat system," theweatherstat, located outdoors, operates in essentially thesame way by turning its own heat supply (andsimultaneously that of the building or zone) on and offso as to maintain its own temperature within itsdifferential. Here the ambient temperature variationwhich causes variation in the timing pattern is the fullrange of "effective" outdoor temperature (including theeffects of sun and wind), which constitutes the heatingload.

29. In electronic systems the ambient temperature atthe timer or cycle is, in effect, held constant by means ofan ambient temperature compensator, and the ON andOFF points are reset by remote temperature elementssuch as a room

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thermostat, an outdoor compensator, or any othertemperature controller suitable for this purpose eitheralone or in combination. Raising the operating range ofthe cycle is equivalent to reduction of the ambienttemperature, and thus increases the percentage of ONtime.

30. In whatever form the principle is applied, timedtwo-position control offers a great advantage over simpletwo-position control in that it greatly reduces the swingsin the controlled variable resulting from a large total lag.Since the controller need not wait until it can detectcyclic changes in the controlled variable and then signalfor corrective action, control system lags have nosignificant effect, and the lags in the heat source anddistribution system serve only to smooth out the "humps"and "valleys" in heat delivery so as to approximate closelythe results of a continuous-delivery system withproportional position control.

31. In timed two-position control, the addition ofheat to the thermostat bimetal is a factor in offset.

32. In analyzing the cycle of a thermostat used inthis type of control, you can see that the control pointmust vary if the bimetal is to heat and cool at differentrates necessary to time the cycle for the various loadconditions. As the outside air temperature decreases, theheat loss from the space increases, and the ON cycle ofthe burner must lengthen in order to replace heat lost atan increased rate. This means that the heating rate ofthe thermostat bimetal must be slower so that the burnerwill remain on longer. It also means that the cooling rateof the bimetal during the OFF part of the cycle must befaster so that the burner will come on sooner. Both ofthese demand that the difference between the bimetaltemperature and the air temperature become greater.This difference is secured by a sustained deviation of theroom temperature, which is called offset.

33. Quantitatively, in timed two-position control,offset is equal to the total added heat minus the manualdifferential of the thermostat. Total heat is equal to thedifference between the maximum temperature of thebimetal and the temperature of the air surrounding it.Manual differential is the differential for which thethermostat is set.

34. Both offset and temperature swing can bereduced to negligible quantities by using a relativelynarrow manual differential (such as 1 ½° or 2°) and asmall amount of artificial heat applied directly to thesensing element.

35. Proportional control. If proportional control thefinal control element moves to a position proportional tothe deviation of the value of the controlled variable fromthe set point. There is one and only one position of the

final control element for each value of the controlledvariable within the proportional band of the controller.Thus, the position of the final control element is acontinuous linear function of the value of the controlledvariable.

36. Because there is but one position of the finalcontrol element for each value of the controlled variable,a sustained deviation is necessary to place the finalcontrol element in any position other than the middle ofits range (assuming the set point to be in the middle ofthe proportional band). Offset therefore becomes amajor problem in proportional position control.

37. As an example, suppose we have proportionalcontrol of a hot water coil used in heating a room.Under ideal load conditions, the thermostat is in themiddle of its proportional band, the coil valve is halfopen, and there is no offset. Now suppose that theoutside temperature drops, increasing the load on theheating coil. At once, more heat is required in steadysupply to replace the heat which is being lost from theroom at a greater rate. To deliver the required heat, thecoil valve must open further and remain in that positionas long as the increased load exits. To do this, thetemperature must deviate from the set point and sustainthat deviation because the position of the final controlelement is proportional to the amount of deviation.

38. As the load condition increases from the ideal,offset increases toward colder; and as the load conditiondecreases from the ideal, offset increases toward warmer.

39. Floating control. Floating control is a mode ofcontrol in which the final control element moves at apredetermined rate in a corrective direction until thecontroller is satisfied or until a movement in the otherdirection is desired. The direction of movementcorresponds to the direction of deviation of thecontrolled variable. Floating control is further dividedinto several subclasses, two of which are of interest to us:

a. Proportional-speed floating control in which thefinal control element is moved at a rate proportional tothe deviation of the controlled variable.

b. Single-speed floating control in which the finalcontrol element is moved at one speed throughout itsentire range.

40. Either is adaptable to systems having a fastreaction rate, a slight transfer lag, and a slow load change.In general, proportional-speed control can be used insystems having somewhat faster load changes than thoseoperating successfully with single-speed floating control.

41. Series 20 Control. The series 20 control circuitacts to make and break an electrical circuit which resultsin two-position response. This con-

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trol is designed for low voltage, two-position control of:a. Motorized valves.b. Motorized dampers.c. Relays.

42. Series 20 control circuits are not "fail safe" andshould not be used where continued operation of thecontrolled equipment would be hazardous if the powerfailed. Series 20 motors (and equipment under theircontrol) remain in whatever position they happen tooccupy at power failure.

43. A series 20 control circuit consists of oneholding and two starting circuits. The motor rotates inone direction only, making a half turn each time one ofthe starting circuits and the holding circuit are completed.The holding circuit is made-at the beginning and brokenat the end of each half turn by a cam and switcharrangement on the moor.

44. Figure 34 illustrates a complete series 20 controlloop. The equipment includes a thermostat, an actuator,a valve, and a control transformer.

45. Let's assume that the temperature in the watertower drops to the set point on the thermostat. Thebellows will contract, causing the R and B leads tocontact. The starting circuit is now established. Themotor is energized and starts to rotate clockwise. As themotor and cam rotate, the right blade of the maintainingswitch makes contact with S-2, and the holding circuit isestablished. The holding circuit is independent of thestarting circuit. Once it is completed, it furnishes currentto the motor, regardless of the thermostat action.

46. When the motor shaft has rotated 180°, the camopens contact S-1. All circuits are incomplete, the motorstops, and the steam valve is now completely open andwill remain open until the red and white leads makecontact in the thermostat.

47. You can see that this is going to cause a rise intemperature of the water. The rise in temperature willbecome sufficient to move the thermostat blade tocontact the W lead. Now the starting circuit isreestablished. The motor is energized and begins torotate once again in the clockwise position. As the motorand cam rotate, the left blade of the maintaining switchmakes contact with S-l, and the holding circuit isestablished. Once again, the motor will rotate a 180°before the cam breaks the holding circuit.

48. The steam valve is closed and will remain thereuntil the thermostat calls for it to open. The control ofthe valve in this manner will produce the two-positionresponse which was pointed out before

49. Series 40 Control. The series 40 control circuitacts to make and break an electrical circuit which results

in two-position response. This circuit is a line voltagecontrol circuit which is switched directly by the single-pole, single-throw switching action of a series 40controller. Series 40 is a two-position control andrequires two wires. It can be used to control fans, lights,electric motors, and other standard line voltageequipment, as well as a series 40 controlled device andline voltage. The series 40 control circuit depends on theequipment under control as to whether it is "fail safe" ornot.

50. In operation the equipment under control isenergized when the controller switch is closed anddeenergized when it is open. Normally the series 40controller makes and breaks the load directly, as shown infigure 35. It is possible for loads to exceed the controllerrating. In this situation a simple control relay is usedbetween the controller and the load circuit.

51. Figure 35 shows a complete series 40 controlloop. It includes a series 40 thermostat series 40controlled device, and line voltage. The thermostat issensing the temperature of the water. A drop intemperature below the set point causes the mercury bulbto rotate, allowing the mercury to close the circuit to thesolenoid valve. The solenoid opens the valve and allowsthe steam to enter and heat the water. This cyclecontinues as the temperature changes, and you can seethat this is ON and OFF control or two-position.

52. Series 60 Control. The series 60 controlcircuits make and break electrical circuits which results intwo kinds of response. Series 60 controls can be used astwo-position and floating response.

53. The series 60 two-position control circuit issimilar to the series 20 except that series 60 is a linevoltage circuit. It can be used for industrial application,using line voltage equipment and installations wheresingle-pole, double-throw control of line voltage isrequired. It is not a "fail safe" control circuit and shouldnot be used where it would be hazardous.

54. The series 60 floating control produces anotherresponse that is different from two-position. Series 60floating control is commonly applied to motorized valveson tank level control systems, motorized dampers forstatic pressure regulation, and specialized pressure andtemperature control systems.

55. The series 60 floating control circuit uses eitherlow voltage or line voltage, depending on the equipmentselected. The basic pattern of the floating control circuitis like that of the two-position circuit except that themotor is reversible and limit switches are substituted formaintaining switches.

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Figure 34. Series 20 control loop.

56. In floating control there is no fixed number ofpositions for the final control element. The valve ordamper can assume any position between its twoextremes as long as the controlled variable remainswithin the values corresponding to the neutral zone ofthe controller. Furthermore, when the controlled variable

is outside the neutral one of the controller, the finalcontrol element travels toward the corrective positionuntil the value of the controlled variable is brought backinto the neutral zone of the controller or until the finalcontrol element reaches its extreme position.

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Figure 35. Series 40 control loop.

57. Figure 36 shows a series 60 two-position andfloating control circuit. You can see that the two aredifferent in the voltage operation as well as in theresponse.

58. Because of the close similarity of the series 20and series 60 circuits, we will not discuss its operation toa great extent. The main difference is that the 60operates on line voltage, whereas 20 uses low voltage.

59. Figure 36, B, illustrates a complete series 60floating control circuit. The equipment includes atemperature floating controller and a floating controlmotor.

60. Referring to figure 36,B, when the temperaturedrops, the controller blade completes a circuit fromcontacts R to B. This causes the motor to energize byline voltage. The capacitor in the circuit causes themotor to turn clockwise, which will establish a correctiveaction of the final control element.

61. The motor moves at a single speed towardopening the valve. It will stop if sufficient heat is addedto raise the temperature on the thermostat to open R andB. If not, it runs until the limit breaks and stops themotor.

62. On a rise in temperature, the thermostat closesR to W. This allows line voltage to go into the motorthrough W and once again energizes the motor. Thecapacitor in the circuit now causes the motor to rotate inthe counterclockwise direction. The motor rotates,

closing the valve, until the temperature is corrected oruntil the limit of its travel is reached by limit switch S2.The motor would remain here until heat causes a rise intemperature sufficient to cause the thermostat to float theblade back to the neutral position if the desiredtemperature is satisfied.

63. Series 90 Control. The series 90 control circuitacts to balance a bridge which results in modulating orproportional control response.

64. The series 90 control circuit is a low-voltagebridge circuit which operates to position the controlleddevice (usually a damper or motorized valve) at any pointbetween full-open and full-closed. It can be used tooperate motorized valves, motorized dampers, andsequence-switching mechanisms.

65. Figure 37 shows a typical application of a series90 control circuit. The temperature of the equipmentcooling space is being controlled by governing theamount of air that moves across the direct expansion(DX) coil. The thermostat modulates to control themodulating motor. The motor, in turn, proportionallycontrols the face and bypass dampers to controltemperature.

66. Figure 38 shows how a balancing relay is made.The balancing relay is applied to the series 90 controlcircuit. The amount of current passing through coils 1and 2 governs the position

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Figure 36. Series 60 control loop.

of the contact blade in respect to the two contacts of themotor.

67. When equal amount of current flow throughboth coils of the balancing relay, the contact blade Is inthe center of the space between the two motor contacts,and the 24 volts cannot be applied to the motor. Yousee that there is current flow in each coil even thoughthe motor isn't running.

68. In figure 38, if coil C1 receives more currentflow, and thus becomes stronger, the contact blade

moves to the left and completes the circuit betweenmotor winding W1 and the transformer. Current alsopasses through the capacitor and W2. The motor willrotate in the clockwise direction. When coil C2 receivesmore current flow, the contact blade will move to theright and a circuit is made once again to the motor. Thecapacitor is now in series with winding W1. You knowthat this causes the motor to rotate in the oppositedirection now.

69. Figure 39 illustrates a bridge circuit which

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is used in the series 90 control circuit. It consists of twopotentiometers and the coils of the balancing relay. Onepotentiometer is located in the motor, and its wiper ismoved by the rotation of the motor. The otherpotentiometer is in the controller, and its wiper is movedby the thermal system.

70. The thermostat is satisfied and the bridge isbalanced. Power (24 volts) is applied to the bridge by thetransformer. There is a path for current flow; in factthere are two paths for current flow. The left circuit hasa total of 135 ohms resistance plus coil C1. The rightcircuit has a total of 135 ohms resistance plus coil C2.The amount of current flow is equal in both circuits.This is called a balanced bridge.

71. Figure 40 illustrates a complete series 90 controlcircuit. It consists of a modulating controller, modulatingmotor, and control transformer.

72. Referring to figure 40, you see by the dottedwipers that the temperature has increased. The wiper inthe controller potentiometer is now at a new position onthe resistance. The left circuit now has 97 ½- ohmsresistance plus coil C1. The right circuit now has 162 ½-ohms resistance plus coil C2. Current will flow in the leftand right circuit, as indicated by the arrows. Accordingto Ohm’s law (E = IR), 25 amps will flow through theleft circuit and .15 amps will flow through the rightcircuit. As a result of the unbalance of the bridge, coilC1 has a stronger magnetic field and coil C2 has a weakermagnetic field.

73. Power is now applied to the motor windings,and the motor begins to rotate. The motor runsclockwise. As it turns clockwise, it moves the wiper onthe motor potentiometer to the right, as shown. Nowthe circuits on the left and right are once again balancedin resistance. The balancing relay is balanced, and poweris broken to the motor. The chilled water valve wasopened during the change of the motor. The

Figure 37. Series 90 application.

Figure 38. Series 90 balancing relay.

temperature rise indicates that more cooling is needed.The series 90 control circuit will continually repositionthe valve to correspond to the changes in temperature.

74. Modulating control is a much better mode ofcontrol that two-position. As you have seen, any changewith modulating control immediately causes aproportional change of the final control element. But wemust remember that if we want to have more accuratecontrol, it costs more.

75. Electrical Actuator Adjustment. We havediscussed the electric controls that may be used to controltemperature, pressure, flow, humidity, and any othervariable. Those controls must be installed, adjusted, andcalibrated properly before they are able to control thosevariables.

76. One of the important items that has to operateproperly is the final control element, such as the damper,louver, valve, or any device that might be used to controlthe control agent.

Figure 39. Current flow at one instant in a balanced bridgecircuit.

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Figure 40. Complete series 90 control circuit.

77. For example, if temperature is being controlled,the control loop may be properly operating to maintainthe temperature. But let us look at the control loop fromthe standpoint that the actuator isn't in adjustment withthe chilled water valve. Now, the control loop cannotpossibly maintain the temperature. Why can't the controlloop be able to control the temperature? Well, look atfigure 41 and we will see why.

78. Figure 41 illustrates a control loop in which theactuator is out of adjustment with the final controlelement. The temperature in the duct is below the setpoint. The controller sensed this and controlled theactuator (modulating motor) in a manner to compensatefor the lower temperature.

79. The controller signaled the actuator to close thevalve so that the temperature could increase. Theactuator moved to this position, stopping at the extent of

its travel. The linkage between the actuator and thevalve causes the valve to remain open, so chilled watercontinues to flow through the coil.

80. With the actuator out of adjustment, the controlsystem will not function properly. So we see why itcannot control. Therefore the actuator must be adjustedto the device it operates.

81. Electrical Control Applications. Electricalcontrols can be applied any time that a measured variableis to be maintained. As you have seen in the previousdiscussions, the controller senses the measured variable,and the final control element regulates the control agentto maintain the measured variable at a set point.

82. Maintaining temperature in a space with series 90control. In figure 42, a system controlling temperature isillustrated. You can see that

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Figure 41. Actuator out of adjustment.

a series 90 modulating control circuit is being used tomaintain the temperature.

83. The thermostat, T-l, is set to maintain a desiredtemperature of 72° F. If, for instance, the temperaturesensed by the bulb is 72° F., the controller operates themotor to position the face and bypass dampers at ahalfway position. This would mean that the bridgecircuit of the series 90 control is balanced because thetemperature is at set point.

84. When the temperature drops below set point(72° F.), the bridge circuit is unbalanced and the motorwill run clockwise to close the face dampers and open thebypass dampers. This allows more air to pass through thebypass dampers. The result is less cooling because less airis cooling in contact with the coil. The series 90 motorruns until the bridge is once again balanced. The motorwill hold the dampers in this position until the thermostatsenses a temperature change which will once againunbalance the bridge.

85. When the temperature increases above set point,the bridge becomes unbalanced in the opposite direction.The controller now causes the motor to rotate in thecounterclockwise direction. The motor now opens theface dampers and closes the bypass dampers. Now morecooling is produced because of the greater amount of aircoming in contact with the cooling coil. The motor willrun (opening the face dampers) until the bridge is onceagain balanced.

86. Operating in this manner, the temperature iscontrolled by this modulating control system.

87. Maintaining relative humidity with series 90 control.If we are to maintain humidity, it first has to bemeasured by a controller. The humidity controllersusually employ hair, leather, wood, or some moisture-sensitive element to sense humidity and to convert it intomovement. This movement, in turn, operates thecontroller.

88. Looking at figure 43, you will see a modulatingcontrol system maintaining humidity. The humiditycontrolled senses the percent of humidity as the airmoves through the duct. This control circuit operates inthe same manner as the previous system which wasmaintaining temperature. The main difference betweenthe two systems is the sensing device which operates thewiper in the controller.

89. As the humidity increases above set point (50percent) the hair expands in length. This allows thespring tension to move the wiper arm on thepotentiometer. The bridge is then unbalanced and theseries 90 motor is started rotating counterclockwise. Themotorized valve is modulated toward close due to theincreased humidity. The motor will continue to run(closing the valve)

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Figure 42. Maintaining temperature with a series 90 control.

until the potentiometer in the motor balances thepotentiometer in the humidity controller.

90. The opposite action occurs when the humiditydrops below set point. The bridge is unbalanced in theleft circuit now. The motor rotates clockwise andmodulates the motorized valve toward open. The motorwill run (opening the valve) until the bridge is balanced.The system will remain here until the humidity changes.

91. Maintaining temperature and relative humidity withhigh limit control. A control system which maintainstemperature and humidity at a high limit is illustrated infigure 44. The system is composed of several units thatwe have discussed before, but in this case they are usedin conjunction with each other. The devices are a series90 motor, thermostat, and humidistat.

92. The control circuit of the temperature controlsystem with high limit humidity is diagramed in figure45. As you can see, the series 90 thermostat has twopotentiometers. The wipers of these pots are moved bythe temperature sensed by the bulb ("pots" is short forpotentiometers).

93. The front pot forms a bridge circuit with theseries 90 motor that operates the face and bypassdampers. The only thing abnormal in this part of the

temperature circuit is the pot of the humidistat being inthe blue wire of the right circuit

94. The rear pot forms a bridge circuit with theseries 90 motor which operates the reheat valve. Therear pot is somewhat out of line with the front pot. Afactory calibration, the "dead" spot is about 7/64 inch.You can see in figure 45 that the wiper in the rear potcannot start to operate the reheat valve at the instant thefront pot wiper reaches B. The temperature must dropfarther for the rear wiper to reach W, where it will beginto unbalance the bridge circuit.

95. If you will refer to figures 44 and 45, we willdiscuss the operation of the control system and its circuitas it functions to maintain the temperature and relativehumidity at a high limit. The set point is 72° F., whichthe control system strives to maintain. We have seenthat the face and bypass dampers will be at midpositionwhen the temperature is at set 'point. It will modulatethe face and bypass dampers to control the temperature.The system operates in this manner until the humidityreaches the high limit.

96. Let us go through the operation when thehumidity increases above the high limit. This

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Figure 43. Maintaining relative humidity with a series 90 control.

Figure 44. Maintaining temperature and humidity with a high limit humidity control.

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Figure 45. Temperature and high limit humidity control circuit.

causes more resistance to be placed in the right circuit.The motor runs clockwise, opens the face dampers, andcloses the bypass dampers. Of course, this allows moreof the air to come in contact with the coil. As a result, agreater amount of moisture is removed from the c.f.m.moved through the duct. In other words, the high limithumidistat overrode the thermostat and caused the face

damper to open more than the thermostat wanted it toopen. Naturally, if the face damper is open more thanthe thermostat is calling for it to open, the roomtemperature will drop below the desired value.

97. The rear pot of the thermostat now comes intoaction. The drop in temperature causes the rear wiper tobegin unbalancing the bridge circuit

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Figure 46. Air compressor station.

of the reheat valve. The reheat valve brings thetemperature back up to the desired amount by addingheat through the steam coil. When the sensible heat isadded, it also lowers the relative humidity. Thetemperature and humidity both have now been satisfiedfor the desired conditions. This system continuallystrives to maintain temperature and a maximum humiditywithin the limits of the controllers.

21. Air Supply1. Almost all large air-conditioning systems require

a supply of compressed air. It is used to operate valves,controllers, transmitters, thermostats, humidistats,receivers, etc. Such air can be furnished to an installationby two possible sources:

a. Compressed air may be available in the buildingby a remote compressor system.

b. Compressed air may be furnished by acompressor station installed within the building. Figure46 illustrates a simple, typical air-supply system. Itconsists of a compressor, storage tank, filter, pressuregauges, safety valve, pressure reducing valve, etc.

2. A Compressor Components. Compressors aremade in a number of different sizes and designs. Theyare driven by electric motors or gasoline engines. Someare the single-stage type, while others are of themultistage type. The multistage compressor is designedto develop higher pressures than the single-stage unit.Compressors are cooled either by air or by a liquidcoolant. Compressor units are mounted in a variety ofways: stationary, on skids, and with single or severalwheels which have rubber tires or steel rims.

3. Most of the air compressors installed in largebuildings are anchored tightly to the floor and are drivenby an electric motor. The compressor is connected tothe motor by a belt-drive arrangement. Belt-drivencompressors usually have more than one belt. If one beltneeds changing, they all must be replaced. New beltsshould be adjusted to specifications and then checkedregularly because they sometimes stretch. The aircompressor is very similar in construction to therefrigeration compressor. Care and maintenanceprocedures are the same.

4. Air cleaners and filters. The air in an aircompressor must be clean to protect the air compressorand other controls and equipment operated by the airpressure. A defective air cleaner will not filter the air.The minute particles in dirty air are apt to restrict theflow of air, reducing the efficiency of the compressor andoperating air controls. Air cleaners may be constructedof screen mesh or may be a filter disc type. No matterwhat type cleaner is used, it must be serviced periodically.Operating conditions will determine the servicerequirements. Regardless of how frequently a cleaner isserviced, you must never use a volatile cleaner such asgasoline or diesel fuel for cleaning purposes. Anonvolatile cleaner is required because, as the air iscompressed, it generates heat and the combination ofcompressed air and fuel plus generated heat leads toexplosions. The higher the compressor pressures are, thehigher the temperature and the greater the emphasiswhich must be placed on safety precautions. A bombexplodes because the internal pressures

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are greater than the housing can stand. Therefore,several safety devices are built into the air compressorsystems.

5. For efficiency and safety, air enters the filter andpasses on to the low-pressure cylinder. As air leaves thelow-pressure cylinder, it is cooled in the intercoolerbefore being compressed in the high-pressure side. Theair must be cooled again in some manner because heatedair doesn't have the body that cold air has under pressure.

6. To clean a dry pad filter, shake out the dirt fromthe element and blow air through the filter in a reversedirection. Then clean the filter with a nonflammablecleaning fluid.

7. Controls. Safety controls are required for acompressed air unit. Pressure regulators, relief valves,safety valves, pressure switches, etc., are some of thedevices for control of compressed air and compressoroperation.

8. Relief valves' are installed in the receiver andintercooler to relieve excessive pressures. Relief valvesand safety pop valves are usually set at the factory andthe setting should not be changed, although some unitsmay be disassembled for inspection. Some installationsrequire special valves in addition to the standard reliefvalves. If a valve is disassembled for service, all partsshould be thoroughly checked. Proper operation of safetyvalves is very important, as the name implies. Excessiveinternal pressures can cause the air compressor unit toexplode, so be sure that only recommended proceduresand parts are employed when servicing a valve. Cleaningis also important so that this valve will not stick open,thus causing the second-stage pressure to drop to zero.

9. Intercooler. In the compressor the air iscompressed and then sent into an intercooler, where it iscooled. The intercooler consists of a tank with coilsthrough which air or water is passed to cool thecompressed air. Under normal operating conditions theair can be kept at a reasonable temperature by use ofaftercoolers. The aftercooler is generally located betweenthe air compressor and storage tank. Its function is tocool the air to a desirable temperature and to condensemoisture out of the air.

10. Air tank. The air tank is a storage facility for thecompressed air. This tank is a sealed unit and willrequire minor maintenance. All piping connections mustbe fit tight, and valves adjusted according tospecifications. The air tank is generally located in a coolplace for efficient unit operation.

11. Chemical drier. A means of removing moisturefrom the air is the use of a chemical drier for absorbingmoisture. After the chemical in the drier has becomesaturated with moisture, it must be reactivated by heat orbe replaced. The drier in the air compressor system is in

many ways similar in construction to the type ofdehydrator used in a refrigeration system. Thedehumidifying cartridge containing the chemical isgenerally placed in the pressure line. One type ofchemical that has been successfully used is calciumchloride. Refer to the manufacturer's manual forrecommended procedures for cartridge reactivation orreplacement.

12. Motor. The motor size will vary with thecompressor size. Refer to the motor nameplate data forspecification. Maintenance such as cleaning andlubrication should be done periodically.

13. Traps and drains. Traps and drains are used toremove moisture that may have accumulated in thesystem. The size of the air control system will determinethe number of traps and drains that are used. Thesecomponents must be cleaned periodically to remove anymoisture that may have collected in the system. Refer tocontrol air system diagram for actual location of thesecomponents. Generally, a trap or separator is locatednear the aftercooler

14. Gauge. Gauge locations will vary with eachcontrol air system. Most gauge locations are visible tothe operator so that he can make an accurate reading onthe air pressure. The air pressure must remain constantfor accurate control operation; therefore a closeinspection must be maintained on gauge readings. Ifthere is a variation in air pressure, the cause must befound immediately and corrected.

15. Maintenance. Before starting the compressor,make sure the crankcase is filled to the proper level witha recommended grade compressor oil. The crankcase isfilled to the line on the oil indicator or oil level elbowlocated near the bottom of the compressor base. Allcompressor parts are oiled from this base reservoir. Aclose check must be periodically maintained on the oillevel for proper lubrication.

16. If the compressor is new, it should be drainedand refilled every 2 weeks of constant operation. Whenthe compressor is "broken in," drain and refill after every2 or 3 months of daily operation or the equivalent.

17. The unit must be kept clean, since dirt isresponsible for most compressor troubles. The air filtersshould be checked periodically and cleaned weekly with anonexplosive solvent or by blowing air through the filtermedia. Make sure dry filters are free of all moisture.The screen type filter should be dipped in oil for betterfiltering action.

18. Special care must be given to make sure that allcomponents are free of moisture. The air storage tankmust be drained of moisture at least once a week and, ifnecessary, more often. Chem-

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ical driers are used for extracting moisture from the air inexcessively humid areas.

19. The belts should be tight enough to preventslippage, but not so tight as to cause excessive strain onthe motor shaft or bearings. V-belts require more slackthan fiat belts.

20. Exhaust and intake valves may become dirtyafter a period of operation. This can result in valveleakage and cutting down on efficient compressoroperation. Periodically, valves should be removed,inspected, and thoroughly cleaned. If they continue toleak after cleaning, they should be replaced. Anindication of valve leakage is any dark spots on the valveseat or polished surface. Pop-off safety valves should beblown off every 6 months to insure against sticking.Reducing valves should be checked periodically to insurethat they maintain the correct system pressure at alltimes.

21. Troubleshooting. If there is a pressure loss inthe receiver, it can be caused by insufficient power unitoperation, slipping drive belt, leaky pipe joints, obstructedair intake filter, obstructed or burned valves, or wornrings. Knocks usually result from insufficient orimproper lubrication, too thin a cylinder head gasket,worn bearings, loose flywheel, or foreign materials on thetop of the piston. If the compressor begins to knock, itshould be shut down immediately and the troublereported so that the necessary repairs or adjustments canbe made.

22. Pneumatic Control System1. The pneumatic control system, illustrated in

figure 47, consists of five major parts. They are:a. Source of air supply.b. Lines leading from the source of supply to the

controllers (thermostats, humidistats, etc.). These linesare referred to as supply pressure lines.

c. The controllers, thermostats, humidistats,recorders, etc.

d. The lines leading from controllers to thecontrolled devices such as valves, dampers, etc. Theselines are referred to as control pressure lines.

e. The controlled devices (dampers. valves, etc.).2. Lines. In order for the controller or any

pneumatic control device to operate successfully, thedevices must be connected to a regulated air supply. Thisair must be clean and dry and supplied at a pressure from15 to 20 p.s.i.g. The installation must be planned toprevent water, oil, or dirt being carried through the pipinginto the control or instruments.

3. All tubing, pipes, and fittings must be cleaninside and free of burrs. Shellac or a recommended jointcompound may be applied sparingly

Figure 47. -Typical air supply system.

to the male threads. All joints should be checked underpressure with a soap and water solution.

4. In reference to figure 48, the supply headerfurnishes air to a series of instruments in a building area.Note that the supply header is pitched 1/4 inch to 1 footto help in the drainage of entrained oil or moisture.Sumps and drains are located in the low points of thesystem and should be blown off daily. The sump can beconstructed of pipe of sufficient volume to hold all thecollected water until it is blown out. Clean brass or ironpipe and fittings ½2 inch or larger should be used for theheader.

5. The tubing that supplies air to the instrumentsshould be taken fi6m the top of the header. This is anadded precaution against letting the moisture enter theinstruments and other controlling devices. Theconnections can be made at the side of the header whennecessary, but never at the bottom.

6. The air connections at the instruments are 1/4-inch National Pipe Thread (N.P.T.), 3/8-inch coppertubing (not less than .300 inch inside diameter (I.D.), or1/4-inch iron pipe standard (I.P.S.). Brass pipe is used forthe air supply piping. Where corrosive conditions requireit, 1/4-inch I.P.S. clean, new, black iron pipe can beused. Copper tubing is most practical and can be keptfree from leaks. The output piping to control valvesshould be ¾3/- inch copper tubing with few exceptions.

7. The air filter and supply pressure regulator,shown in figure 48, are installed in the supply pipingimmediately before the instrument. These componentsmust be firmly supported to prevent the sagging oftubing. Arrows on these devices indicate how they mustbe connected in the system. Shutoff valves are installedin the system to enable the repairman to remove deviceswithout shutting off the whole air-supply system.

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Figure 48. Air distribution piping.

8. The air filter catches any moisture, dirt, oil, andother foreign materials that may pass through the systempiping. Most filters have a rated capacity as to theamount of moisture they can hold; therefore, they mustbe checked and drained periodically. Normally, thisoperation should be done daily, but under severeconditions of heavy moistened air it must be done morefrequently. Close attention must be given to this detailfor efficient and successful instrument and controloperation.

9. The filter may be serviced by removing thebottom cover and removing the filtering element. Thefilter may be cleaned with an approved cleaning solventor compressed air. Whenever the filter element looks toodirty, it should be replaced with a new element.

10. Pneumatic piping for instrumentation in largeinstallations becomes complicated. Many instruments arelocated at designated positions in the duct system andmust have compressed air piped to them; therefore it isadvisable to refer to the installation schematic drawingswhen determining the exact location of piping andassociated controls.

11. Reducing Valve Station. The supply pressurefor most single temperature controllers runsapproximately 15 p.s.i. Figure 49 illustrates an air filterand a reducing station for a single pressure system.Where two or more controllers or temperaturethermostats are required, a dual-pressure system is used.The supply pressure for a dual installation isapproximately 15 to 20 p.s.i. Figure 50 shows a reducing

valve station for a dual pressure system and illustrates avalve and switch for selecting either of the two pressures.

12. In most installations the air piping for thecontrol system is concealed internally into the buildingstructure. Generally, very little servicing is requiredunless there is some possible damage due to buildingalterations. Piping in the fan and equipment rooms isoften exposed. In most instances the exposed lines arerun along out-of-the-way places with properly designedsupports and hangers. Extra precautions must be takenso that the lines do not become damaged.

13. Instruments and Controls. Automatic controlsare designed to do a specific job in an air-conditioningsystem. The controls may open

Figure 49. Single-pressure system.

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Figure 50. Dual-pressure system.

or close valves and dampers, and operate other equipmentautomatically whenever the need arises. Years ofresearch have gone into the design of these controls; andif they are properly installed and maintained, they willfunction efficiently. The type and number of electric andpneumatic controls used will vary with the size of air-conditioning installation and with equipment usage in thebuilding.

14. In equipment cooling, many different types ofinstruments and controls are needed to control theconditioned air at a required temperature and humidity.All instruments, whether they are recording, indicating, orcontrol type, must operate and record accurately. Youlearned earlier in this chapter that special care h given tothe compressed air supplied to the controls. It must be aclean, dry air and supplied at approximately 20 p.s.i.g.This air pressure initiates control operation.

15. Location. The location of controls andinstruments will vary with each air-conditioninginstallation. Generally, a control is mounted near thedevice it operates. For example, a damper motor isusually located near the damper it operates. To find theexact location of controls, refer to your installation air-conditioning drawings.

16. All controls and instruments must be installed ina clean, dry location. They must be mounted securely toprevent sagging or vibration and must be accessible forcleaning, adjusting, and repair.

17. Terminology. Before you can understand theoperating principles of controls, you must know the termsthat are applied to instrumentation. The following is alist of some of the most common terms and theirmeanings:

a. Direct-acting controller is a control that isadjusted to give an increasing air output pressure with anincrease in the variable, whether it is temperature,pressure, flow, vacuum, or liquid level.

b. Reverse-acting controller is a control that isadjusted to give a decreasing air output pressure with anincrease in the variable, whether it is temperature,pressure, flow, vacuum, or liquid level.

c. Direct-acting diaphragm valve is a valve thatcloses when the air pressure is applied to its diaphragmmotor. It may be referred to as an air-to-close valve.

d. Reverse-acting diaphragm valve is a valve whichopens when the air is applied to its diaphragm motor. Itmay be referred to as an air-to-open valve.

e. Set point is the value of the controlled variablethat is asked of the controller by setting the indicator tothat value.

f. Control point is the actual temperature, pressure,flow, vacuum or liquid level at any given instantregardless of what the set point may be.

g. Proportional control is the type of control actionwhere the control signal varies in proportion to changesin the controlled variable, and may be any value fromminimum to maximum.

h. Sensitivity of a controller is the ratio of outputpressure change to the movement of the pen orindicating pointer.

i. High sensitivity results in a large output pressurechange for a given pen or pointer movement.

j. Low sensitivity gives a small output pressurechange for a given pen or pointer movement.

k. Throttling range is used to designate thesensitivity of a controller and is expressed as themovement of the pen or pointer in percent of chart, orscale, width necessary to cause a full opening or closingof the control valve.

l. Automatic reset response is only used whenautomatic reset is adopted to the controller. It is anadditional output pressure change resulting from a controlpoint change and provides at a rate dependent upon theproportional response. It acts in the same direction asthe proportional response and continues until the setpoint and control point are together.

m. Reset action is the control action in which thecorrections are made in proportion to the time acondition has been off and the amount of deviation.

n. Controlling medium is the liquid, vapor, or gas,the flow of which through the diaphragm valve is variedin accordance with the demands of the process.

o. Processed or controlled medium is the liquid,vapor, gas, or solid which is to be maintained at aconstant value by varying the flow of the controlledmedium.

p. Load change is any factor which requires achange in the flow of the controlling medium in order tomaintain the control point of the process.

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Figure 51. Spiral bimetallic thermostat.

These factors may include a change in the temperature,pressure, rate of flow, or composition of either thecontrolling or the controlled medium.

q. Hunting is the changing or variation of thecontrolled variable about the control point, generallycaused by excessive diaphragm valve movement.

r. Wandering is an irregular shift of the controlledvariable about the control point resulting from frequentload changes.

18. Thermostat. The thermostat is a nerve centerof heating and cooling control centers and operates eitherpneumatically or electrically. The thermostat is asensitive unit that responds to changes in roomtemperature and indicates where more or less heat isrequired. It transmits its indicating signal to the primarycontrol for action. On an electric thermostat this is doneby the making and breaking of electrical contact withinthe thermostat itself; within the pneumatic thermostat apressure relay regulates the air to the controlled unit.

19. Thermostats usually differ in constructionaccording to the type of primary control with which theyare used. Probably the most common type of thermostatis the spiral bimetallic type shown in figure 51.

20. Figure 51 illustrates a remote bulb typethermostat. This type of thermostat is used ininstallations where severe vibration may exist at the pointof measurement, or where it is desirable to have aninstrument at a central location. The capillary tubeshown in figure 52 is usually a liquid-filled element. It issensitive to temper-

Figure 52. Remote bulb thermostat.

ature changes and will control temperature accordingly.21. Another type of thermostat frequently used is a

bellows type shown in figure 53.22. Location. The location for a thermostat should

be representative of that part of the building where arequired temperature is to be maintained. It should beinstalled where it will be exposed to free circulation ofair, free from drafts, and away from the direct rays of thesun or any type of radiant heat.

23. Maintenance. The internal mechanism of athermostat should be cleaned of dust and dirt. Thecontacts should be cleaned by drawing a piece of hard-finish paper (such as a common post card with a hardsmooth finish) between the contacts. Never use emerycloth or other abrasives to clean the contacts. Forrecommended procedures or part replacement. refer tothe manufacturer's maintenance manual.

24. Humidistat. Figures 54 and 55 illustrate

Figure 53. Bellows type thermostat.

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Figure 54. Room humidistat.

room and insertion type humidistats. The humidistat isdesigned for the accurate control of the addition to orremoval of moisture from air in a system or space.Room humidistats are available with various elementsconsisting of wood, hair, or animal membrane withadjustable sensitivity. Insertion humidistats are designedfor accurate control of the relative amounts of moisturein heating, ventilating, and air-conditioning ducts.

25. Operation. Under normal operating conditions,the humidistat will control the humidity within 1 percentrelative humidity. Most humidity controls operateelectrically to regulate dampers, valves, or other regulatingdevices. For example, when a humidifying device havinga spray nozzle is used, a solenoid valve is ordinarilyinserted ahead of the nozzle. A humidistat in theconditioned space energizes the solenoid when therelative humidity drops below the humidistat setting. Assoon as the humidity in the conditioned space is broughtup to that required to satisfy the humidistat, the circuit isopened and the solenoid shuts off automatically.

26. Maintenance. The humidistat is a very delicateinstrument and must be handled with

Figure 55. Insertion type humidistat.

Figure 56. Hygrometer with motor-driven fan.

care. The instrument must be encased at all times andkept free of dust and other foreign materials. It must bemounted securely and located where there is a goodcirculation of air through its mechanism. All adjustmentsmust be made with special precautions since they are verysensitive devices. Refer to the manufacturer's manualsfor recommended maintenance and adjustmentprocedures.

27. Hygrometers. The hygrometer is a device usedto measure, record, and control humidity. There aremany types and designs of these instruments made byvarious manufacturers, but their principles of operationare similar.

28. The hygrometer gives instantaneous readings ofa measured area and will regulate valves or other controlsto maintain a necessary humidity.

29. There are two types of hygrometer instruments.They are referred to as recording and recording-controlling types.

30. Figure 56 shows a recording-controlling typehygrometer. This instrument is installed in the area inwhich the humidity is to be measured. When theinstrument is installed within an area, the air to bemeasured is circulated through the wet- and dry-bulbhousing by a suction fan, as shown in figure 56. The fandraws the air through the bulb housing by use of anintake and exhaust port, usually located in back of thepanel housing, creating conditions similar to those whichpsychrometric tables are obtained. In applications wherebulbs of hygrometers must be located inside an apparatus,room, or duct, and where a continuous source of watersupply is not available, a water feed instrument, asillustrated in figure 57, is used. The water supplied to theinstrument must be cleaned and constant.

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Figure 57. Water feed hygrometer.

31. Operation. The operating principles of ahygrometer are similar to the operating principles of asling psychrometer, while on a hygrometer thesetemperatures are transmitted through a Bourdon tube toan instrument mechanism which records the temperatureand humidity. Refer to the manufacturer's manual forspecific hygrometer instrument action.

32. Maintenance. The instrument mechanism issimilar in construction to the type used in transmittersand recorders, a explained later in this chapter; thereforeits components can be maintained in the same manner.The major difference in hygrometer construction is theaddition of water to the wick. The water and wick mustbe kept clean r accurate instrument operation. Periodiccleaning of the wick is required. Refer to manufacturer'smaintenance manuals for specific instructions formaintenance and adjustment procedures.

33. Controlled Operator. Controlled operatorsrequire position changing according to variations of acontrolled medium. For example, damper operatorsposition dampers in many ways to regulate airflow, someof which are illustrated in figure 58. Blades may be usedin parallel or opposed operation, depending on their usein duct system.

34. Damper operators. The damper operator isgenerally of the piston type, a shown in figure 59. Thepiston is attached to an operating stem

Figure 58. Damper control air movement.

and, as air is applied to the diaphragm, the piston isforced to move outward, causing the stem to move in thesame direction. This forces a tension on the spring. Theair that is fed from the controller to the damper operatorusually ranges from 0 to 15 p.s.i., different spring rangesare available for different applications. Generally, 5-to l0p.s.i. spring range is the most commonly used springdesign tension; and with such a spring tension, theoperator is in normal position when the control pressureis 5 p.s.i., a illustrated in figure 59. It is in its opposite-to-normal position when the control pressure is above orbelow 5 p.s.i. under normal load conditions. At

Figure 59. Piston damper operation.

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Figure 60. Diaphragm valve.

5 p.s.i., the operator assumes a midposition which isproportional to the air pressure.

35. Operators are generally mounted on the damperframe wherever possible and are connected directly to adamper louver. They can be mounted externally on theduct and operate through a crank arm on a shaftextension to the damper louver.

36. Pneumatic valves. Pneumatic valves consist of adiaphragm or bellows and a spring. Figure 60 illustrates atypical diaphragm valve. Its operation is very similar tothat of the damper operator. The valve spring acts toeither open or close the valve in accordance with theapplied air pressure. The bellows type valve is generallyused on convector, unit ventilators, and radiators wherespace is more restricted. Diaphragm valves are generallyused on larger cooling and heating coil installation.There are many types and designs

Figure 61. Valve with positioner.

Figure 62. Damper operator with positioner.

of valves to meet various requirements. Each type willhave its own specific performance rating.

37. Positioner for operators. Figures 61 and 62illustrate how a positioner can be applied to a valve ordamper operator. The positioner provides a means ofgetting greater accuracy in positioning an operator andalso increases the repositioning power.

38. In reference to figures 61 and 62, note that thepositioner has a supply-air connection. Internally it hassupply and exhaust valves like a pneumatic relay. Thevalves are operated jointly by the pressure from thecontroller and by the spring attached to the operatorstem. A small change in control pressure can produce alarge change in pressure on the operator until the stemmoves sufficiently to cause the spring to stop theoperation.

39. When positioners are used, the springdetermines the operating range of the valve or damperoperator. The range can be adjusted over a wide limit.

40. Maintenance of controlled operators. One of themost important things to remember when inspecting adamper operator is to make sure the stems or levers areclean. They must be lubricated as required. Keeping theunit clean is very important. If the diaphragm needsreplacing, the following procedure is recommended:

a. Remove the cylinder head and throw away olddiaphragm.

b. Place new diaphragm in its proper position.c. Roll back flange and insert the piston in the

diaphragm.d. Place the assembly on the upper end of the

cylinder with the loop of the diaphragm between thepiston and the cylinder wall. Make sure that thediaphragm does not wrinkle.

e. Put the cylinder in place with the air connectionin the desired position and tighten the screws uniformly.

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Figure 63. Exploded view of diaphragm valve.

41. The damper must be checked periodically forrust and corrosion. If corrosion deposits are found, theyshould be removed immediately with a steel brush, andthe surface should be repainted. All pivots, linkage, andlevers should be cleaned to remove dirt and other foreignmatter is that they may operate freely.

42. The following components of a valve should bechecked periodically and replaced if found unserviceable:

a. Leaky or worn diaphragm.b. Leaky packing nut.c. Worn or pitted valve or valve seats and disks.d. Weak or broken spring.e. Corroded or dirty valve stem.

43. Figure 63 shows the exploded view of adiaphragm valve. Note the positions of each componentin this valve. Care must be taken when replacing therubber diaphragm. A kinked diaphragm will cause erraticoperation.

44. Controllers. Controllers are used to regulatevalve, dampers, and other devices by me of pressure ortemperature. Because there are so many different designsof controllers, it is impossible to cover each controllerdifference in this memorandum. To understand thespecific operation, maintenance, and calibration of anyinstrument or control, always refer to the manufacturer'smanual in this section a general discussion will be givenon controller operation, maintenance, and calibration.Figure 64 illustrates a typical controller. This type ofcontroller records graphically the variations intemperature or pressure of a measured process.

45. Operation. Figure 64 illustrates a typicalcontroller installation. The purpose of the controller inthis system is to control the temperature of a process byoperating a direct-acting diaphragm valve on a steamsupply line. To understand its operation, let us assumethat the temperature of the process is below that forwhich the controller is set. Because the temperature islow, the air regulating mechanism in the controller allowsthe valve to remain open, ,allowing more steam to flowinto the process. As the temperature increases towardthe control point setting, the bulb measures this increase.As soon as the control point is reached, the Bourdon tubeuncoils. This action forces a change in the internalpressure regulating mechanism in the controller andforces air pressure down on the regulation valve, forcingit to close.

46. Maintenance. The chart on the controller mustbe replaced periodically. The chart on most controllerscan be removed easily by disengaging the pen from thechart and removing the chart from the hub. Place afresh chart on the clock hub and rotate it until thecorrect time line is opposite the reference arc, which isusually indi-

Figure 64. A typical controller installation.

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cated on the control face. The clock face generally hassmall pins or clamps mounted in it, the purpose of whichis to hold the paper and serve as a means of driving thechart.

47. You should fill the pen with manufacturer'srecommended grade and type of ink. Generalinstructions as to how to fill the pen are supplied with theink. Occasionally it is necessary to wash the pens withwater or alcohol.

48. If the pen fails to touch the chart paper becauseof insufficient tension on the pen arm, bend the pen armslightly toward the chart so that the pen touches thechart lightly. If the pen fails to follow the time line,adjust the chart so that a time line corresponds to thereference arc. Bend the pen so that it rests on the timeline matching the reference arc.

49. The following precautions should be followed toimprove controller efficiency and operation:

a. Do not allow water or steam to come into directcontact with the instrument. If it is necessary to washout pipes, tanks, or other apparatus with steam or hotwater, remove instrument bulb first.

b. Do not subject the pressure element ofinstrument to a higher pressure than maximum range ofthe chart unless the instrument is designed to take careof it.

c. Do not allow the controller door to remain openlonger than is necessary.

d. Blow out the compressor receivers periodically toremove moisture and other foreign material.

e. Blow out moisture traps at regular intervals.50. Calibration. The procedures you will study here

are considered as basic control calibration for most typesof controls-pneumatic, electric, and electronic. Thecontrol manufacturer furnishes pamphlets with hiscontrol to guide you in servicing and calibrating a specificcontrol. The basic procedures are:

a. Set the controller set point to the sensedvariable-temperature, pressure, humidity, etc.

b. Adjust the controller to the midrange of thecontrolled device.

c. Set the dial to the desired value.51. Transmitters. The transmission system consists

of a transmitter and a receiver. The transmitter andreceiver with their connecting tubes and accessories forma system that measures the magnitude (temperature orpressure) of a process change and indicates this value atthe receiver.

52. The transmitter or receiver may be either anindicating or recording type instrument. Theseinstruments can be used as temperature or pressuretransmitters, depending on the type of variable that needsto be measured.

53. Temperature transmitter. In using the temperaturetransmitter, the bulb of the tube system is placed in theapparatus to be measured at the point where thetemperature is to be controlled and where the circulationis a maximum. It should not be too close to a radiatingcoil or an open steam inlet.

54. If the bulb is to be placed into a separable bulb,well, or stem, these units should be fitted into theapparatus first. Then insert the bulb and tighten thecoupling nut.

55. Installations where a well is-furnished with athermospeed sleeve must be given special consideration.To install a bulb with thermospeed sleeve, first separatethe bulb from the well. Then screw the well tightly intothe apparatus. Start the bulb into the well carefully toavoid any damaging. Force the bulb as far as it will gointo the well, then tighten sufficiently to hold the bulb inplace.

56. If the tube system is of a vapor pressure type,make certain the elevation of the bulb with respect to theinstrument case is the same as that for which thecontroller is designed. Should the elevation be slightlydifferent, it will be necessary to reset the pen to agreewith the reading of an accurate test thermometer. Bulbelevation data will be given on the data plate of theinstrument or in the manufacturer's maintenancemanuals.

57. Pressure transmitter. Where pressure transmittersare used to measure the pressure of hot, moistatmosphere, a condensate loop should be installedbeneath the instrument. The added pipe length protectsthe instrument from the effect of high temperature, andthe loop retains condensate when the apparatus is shutdown.

58. If the medium being measured is corrosive, thepressure element should be protected by use of a purgesystem or suitable sealing liquid.

59. Operation. Figure 65 illustrates schematically atransmission system which measures the temperature of aprocess.

60. The transmitter shown in figure 65 is actuatedby a Bourdon tube. With an increase in processtemperature, the Bourdon tube tends to uncoil andactuates components in a pressure mechanism. Themechanism, in turn, establishes an equilibrium at a newoutput air pressure, proportional to the pointermovement. The output line from the transmitter isconnected to a bellows of a receiver, as shown in figure65. The air pressure within the bellows actuates the penof the instrument. The receiver pen then records valueswhich are identical to those indicated to the transmitterpointer.

61. The dotted portion of figure 65 illustrates thereceiver controller. This part of the instrument

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Figure 65. A typical transmission system.

regulates a valve which controls a fluid or gas entering aprocess.

62. Maintenance. The transmitter or receiver mustbe mounted on a wall or panel where it will be free fromvibration. It should not be installed where extremetemperatures may damage the delicate components.

63. The chart must be replaced at designatedperiods. Replacement procedures will vary withinstrument design. Some transmitters are designed touse a type of disc chart similar to the one shown infigure 65, while others use a chart in the form of a roll.When a chart is replaced, care should be exercised to setit at the reference point so that the chart will recordaccurately for the particular time.

64. The pen must be filled with a recommendedinstrument ink. If the ink does not flow, start it flowingby touching the pen with the filler. Dried ink may beremoved by washing the pen with warm water. If thepen fails to touch the chart, bend the pen arm inward sothat it will hear lightly on the chart. If the pen does notfollow the reference arc, adjust the length of the pen armby bending the pen point to a length indicated by thetime reference arc on the chart plate.

65. Temperature and Pressure Recorders. Thetemperature or pressure recorders operate on the samegeneral principles as other type controls. The Bourdontube principle is adapted to the recorder operation. Thetemperature or pressure recorder is used to recordgraphically the temperature or pressure of a process orapparatus operation. The thermal bulb attached to the

recorder is placed in the process that is to be measured.Any change in the process temperature is transmittedthrough the Bourdon tube to the recorder mechanismand is shown graphically on the recorder chart. Figure 66shows a typical type temperature or pressure recorder.

66. Figure 67 illustrates a typical temperaturerecorder installation. The connecting tubing from therecorder is placed in such a position that it will notreceive additional heat from heat surfaces such as boilersradiators, pipes, etc. The bulb of the instrument is placedat the point where circulation is best. This is necessaryfor an accurate measurement and recording.

67. Figure 68 illustrates a typical pressure recorderinstallation. On liquid line installations excessivepulsations may occur; in such a condition, a needle valve,as shown in figure 68, is installed in the line. The oilseals are installed in the line to prevent excessivepressures and corrosive liquids from damaging theinstrument.

68. The components of a temperature or pressurerecorder are similar to other types of controllers andtransmitters; therefore maintenance procedures aresimilar.

69. Chan replacement is done periodically. Whenreplacing a chart, make sure the chart is inserted properlyinto the pins or clamps mounted on the clock hub.Rotate the chart until the correct time line is opposite thereference arc inscribed on the control face. Specialguides attached to the recorder door generally hold thechart flat against the plate.

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Figure 66. A typical recorder.

Figure 67. Temperature recorder installation.

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Figure 68. Pressure recorder installation.

70. Adjusting and cleaning of the pen is done asdiscussed previously in this chapter.

71. Recorders are calibrated and adjusted to testingconditions at the factory. Do not make any adjustmentsunless it is certain that the instrument is out ofadjustment. Refer to the manufacturer's maintenancemanuals on procedures for calibration of their instrument.

72. The following precautions must be observedwhen using a temperature or pressure recorder:

a. Never allow a stream of water or jet of steam tocome into direct contact with the instrument mechanism.

b. Never wash or flush out pipes, tanks, orapparatus with steam or hot water, as it might allow thebulb of the instrument to reach a higher temperaturethan maximum range on the chart unless the instrumentis designed to take care of these high temperatures. It isrecommended that the bulb be removed when cleaningthe apparatus.

c. Never subject the Bourdon spring of a pressurerecorder to a higher pressure than the maximum range ofthe chart unless the instrument is designed for higherpressures.

d. Never allow the door of the instrument toremain open any longer than necessary. Keep theinstrument clean and free of dust and other foreignmaterials.

73. Electric Fire Protection Control. The purposeof the fire protection control is to protect the installationagainst the spread of fire by automatically switching offair-conditioning fans and closing dampen. If a fire starts,fans become quite a hazard by increasing the intensity ofthe fire and helping it circulate through fire walls andfrom room to room. Most air-conditioning systems thatuse fan installations use some type of fire protectiondevice in connection with these fans.

74. Operation and construction. The back plate andhelix tube of a fire protection control is made of steel to

form a strong incasement. The sensitive bimetal helixreacts instantly to a temperature change, the rotation ofthe helix being transmitted by a cam or roller follower toa switch. The electrical contacts are enclosed in adustproof case, and the contacts are opened by the camor roller follower in the event the air temperature aroundthe helix exceeds the cutout setting.

75. The cutout point is adjustable, approximatelyfrom 75° F. to 160° F. It is provided with a dial stop toprevent the adjustment from exceeding a maximum of125° F.

76. The cam has both a high and low limit stopand will not rotate forward to the ON position even ifthe fire comes in contact with the bimetal helix. If thetemperature becomes high enough to reach the cutoutsetting, the control may lock out and will require manualreset before the unit may be placed back into operation.The manual reset lever is exposed for easy setting ;and islocated on the control housing. Removal of the coverexposes the instrument terminals and wiring.

77. Maintenance. Field repairs are not recommendedby the manufacturer. If the control is not functioningproperly, it is recommended that the unit be replaced.

78. Airflow Detector and Control. The air-flowdetector type instrument is used to control and detectairflow movements.

79. Operation. The airflow instrument contains aheat source within its flow-sensing leg and operates onthe principle of heat transfer. The electrical mechanismin the ambient compensating leg is actuated wheneverthere is a change in rate of flow beyond the set point ofthe unit. If there is a greater transfer of heat away fromthe flow-sensing leg containing the heat source than thatfor which the unit is set, the contacts in the electricalmechanism remain closed. If the heat transfer is lessthan the set value, the contacts of the electricalmechanism will open.

80. Since this device actually controls an electricalcircuit by a switch action, it can be used to, control fans,alarm systems, air circulators, and other air-conditioningand dust collecting systems.

81. Maintenance. The airflow measuring instrumentshould be placed in a duct area with the two legs side byside in the airflow stream. The electrical connectorshould face either downstream or upstream. It can beplaced in other directions, but this results in somecalibration changes. The set point is generally set bychanges in turbulence, but the instrument may be locatedin a turbulent region if it is calibrated in position.Airflow measuring devices require very little maintenancesince they are hermetically sealed. It is recommendedthat the instrument be replaced if you find that it is notfunctioning properly.

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Figure 69. Schematic of an air-conditioner system.

82. Calibration. With the instrument installed,energize the heater for approximately 5 minutes to obtainan equilibrium. The airflow through the instrumentshould be maintained at the desired point forapproximately 1 minute. Proceed to adjust theinstrument to the point where electrical contacts justoperate. Simulating decreased air-flow conditions or dirtyfilters may be accomplished by blocking off a section ofthe clean filter media. It is recommended that you referto the manufacturers' maintenance manuals for specificinstructions on calibration for their instrument.

83. Control System Operation. So far in thischapter you have not been shown how controlinstruments are used in a control system. Figure 69 is asimple sketch of a control system and illustrates operationof a heating and ventilating fan air-conditioning system.

84. In reference to figure 69, insertion thermostatT2 measures the temperature of return air and regulatesmodulating motor valve V2 in accordance with the heatmeasured in the conditioned area. The insertionthermostat T3 measures the temperature of the dischargeair into the conditioned area and adjusts V2 to keep theair from entering the conditioned area at too hot or toocool a temperature. As the return air rises intemperature, T2 will close valve V2; and if the aircontinues to rise in temperature, T2 will shift the controlof damper motor M1 to insertion thermostat T1 to take

in a volume of outdoor air for cooling. This quantity ofair will vary with the outdoor air temperature to keep theair that is entering the coil at-the setting of T3.Humidity controller HI operates a solenoid valve V1 toadd moisture to the air when required. A control panel isused to monitor all operations and control the positioningof the dampers and the closing of the dampers when thefan stops.

85. Special procedures must be followed whenreplacing an instrument or control that is not operatingproperly. Since every air-conditioning control system hasits design differences, it is impossible to give specificinformation or replacement procedures. It isrecommended that you refer to your installation SOP,and ask your supervisor for information regardinginstrument or control replacement procedures.

CAUTION: Check all system components for properoperation before adjusting, repairing, or replacing acontrol. Many times, controls are functioning properlybut the equipment they control needs servicing.

23. Graphic Panel1. The graphic panel, as the name implies, is a

graphic illustration showing flow diagrams, recording andindicating devices, switches, and controlled equipmentused in a building. The graphic panel in an air-conditioning installation shows

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Figure 70. Sectional view of a graphic panel.

graphically the complete installation with indicating,recording, and control instruments. These instrumentsarc mounted in such a position, with appropriate symbolsand flow lines that they represent schematically thesystems they monitor and control. The graphicillustration will vary with the size and necessaryinstrumentation required in the building air-conditioningsystem. The panel is assembled from one or moresections and is so arranged that the operator monitoringthe controls can easily see the lights, controls, andinstruments mounted on the graphic panel. Some of thecontrol instruments on the panel that can be used are:fan and pump control switches; damper controls;pressure, temperature, and humidity indicator andrecorders; and associated controllers with manual,automatic, and cascade controls. Pilot lights on the panelgive a continuous information concerning the operationof fans, pumps, and other equipment.

2. The graphic panel illustrated in figure 70provides a graphic representation of refrigerationequipment, pumps, fans, and flow lines. The pilot lightsindicate the operation of the cooling tower fans, chilledwater pumps, and condenser water. The chilled watertemperature is always indicated and recorded. Completemonitoring of the controls is done by. means of selector

switches, pushbutton switches, and recording controllersto provide remote control of equipment as represented onthe panel.

3. The graphic panel shown in figure 70 is only asectional view of an air-conditioning system; if the othersections were shown, the complete air-conditioningsystem would be graphically illustrated.

4. Most graphic illustrated panels use colors toidentify components and flow lines. The following colorscan identify most components, but this color code systemmay not be standard on all graphic panels.

Steam flow lines and heating coil..........................RedCooling water now lines and cooling coil ............BlueCondenser water line..........................................GreenDuck work............................................................BlackControl wiring and piping ................................YellowBackground ..........................Tan, gray, blue, or green5. The sections of the panel generally illustrate the

following systems and controls:(1) The refrigeration system.(2) Water circulating systems.(3) Air systems.(4) Room induction system and exhaust fans.(5) Interior zones.

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(6) Temperature and flow recorders andindicators

(7) Building air-conditioning system.6. The graphic panel can be installed in any

available space a building. It is generally installed insidea room, away from the operating refrigeration equipment.The advantages of having the panel installed in a separateroom are cleanliness, less noise, and better lightingfacilities. In some installations the panel is mounted inthe same room as the operating equipment.. Thisarrangement allows the monitoring operator to be indirect contact with the refrigeration equipment operatorin case trouble develops in the air-conditioning system.In either case, the monitoring operator must be in contactwith tie equipment operator at all times by voice orthrough an annunciator system. Close cooperationbetween all operating personnel is very important forefficient and effective equipment operation. In someinstallations, more than one graphic panel is installed inthe building for a more complete monitoring system.

Review Exercises

NOTE: The following exercises are study aids. Write youranswers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the test. Do not submit your answers for grading.

1. What principle of operation does a thermostaticexpansion valve use? (Sec. 18, Par. 6)

2. The control response a motor control uses is_____________. (Sec. 19, Par. 2)

3. How would you set a LPC for a widerdifferential? (Sec. 19, Par. 5)

4. At what pressure will the compressor cutoff ifthe LPC settings are 40 p.s.i. and 15 p.s.i.? (Sec.19, Par. 9)

5. You have received a complaint from themesshall. The newly installed walk-in, used forfresh vegetables, is too cold. The system usesan automatic expansion valve and a low-pressuremotor control. How would you correct thebelow-design temperature in the walk-in? (Sec.19, Par. 10)

6. An ice cube maker is out of order. You findthe storage bin is nearly empty. Aftertroubleshooting the system you locate thetrouble in the bin thermostat. Whatmalfunction most probably caused thethermostat to become inoperative? (Sec. 19,Par. 12-15)

7. You find the air conditioner is not operating andthat someone has inked the feeler bulb of theTMC. What has caused the air conditioner tobecome inoperative, and how would you correctthe malfunction? (Sec. 19, Par. 20)

8. Why are snap action and mercury switches usedin electric controls? (Sec. 20, Par. 2)

9. What type of short exists when the ohmmeterconnected to a terminal of the TMC and theTMC case indicates zero ohms? (Sec. 20, Par.7)

10. Which mode of electric control would you useto operate a refrigeration unit? Why? (Sec. 20,Par. 13)

11. A simple two-position control is used to open aset of louvers when the temperature is 80° F.and to close them when it is 70° F. What is thecontrol point temperature? (Sec. 20, Par. 18)

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12. How does the timed two-position control differin response from the simple two-positioncontrol? (Sec. 20, Par. 24)

13. How is the heating rate of a bimetal element ina thermostat dampened? (Sec. 20, Pars. 31 and32)

14. You are installing a cooling coil that is used tocool an area within close tolerances. What typeof control would you install? Why? (Sec. 20,Pars. 35-37)

15. The controls for a system used for heating andcooling must be replaced. The new controlsystem must operate gas valves for heating andrelays for cooling. Lag time is not a problem.What type of control would you install? (Sec.20, Par. 41)

16. How is the rotation of a series 20 motorcontrolled? (Sec. 20, Pars. 43-46)

17. Which type of electric controls acts similar to asingle-pole, single-throw switch? (Sec. 20, Par.49)

18. The series 60 motor used on a motorized valveto maintain a liquid level in a tank is burned out.Can you substitute it with any series 60 motor?Why? (Sec. 20, Par. 55)

19. Can you substitute a series 60 two-positionmotor for a series 20 motor? Why? (Sec. 20,Par. 58)

20. How does the amount of current flowingthrough a series 90 balancing relay affect theoperation of a series 90 control? (Sec. 20, Pars.66-68)

21. When will the series 90 motor stop running?(Sec. 20, Par. 73)

22. The damper in a duct system is dosed, but thecontrol is calling for e airflow. What has mostprobably malfunctioned? (Sec. 20, Pars. 79 and80)

23. What is the main difference between a series 90humidity control system and a series 90temperature control system? (Sec. 20, Par. 88)

24. Which side of the bridge would be the properplace to connect a humidistat for high limitcontrol in a temperature control circuit? (Sec.20, Par. 93)

25. One belt of a three-belt set driving an sircompressor is broken. How many belts wouldyou install? Why? (Sec. 21, Par. 3)

26. What would you suspect if the air compressorbegins to lose efficiency? (Sec. 21, Par. 4)

27. The first stage of a two-stage compressor isoperating normally but the output of the secondstage s zero. The compressor has an intercoolerbetween stages. What has caused the second-stage pressure to drop to zero? (Sec. 21, Par. 8)

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28. You have just finished installing an aircompressor. What should you check before youstart the compressor? (Sec. 21, Par. 15)

29. What will probably occur if you replace astandard air compressor head gasket with a thinhead gasket? (Sec. 21, Par. 21)

30. What are supply-air lines? Control air lines?(Sec. 22, Par. 1)

31. How much pitch must you allow for a supply airheader 12-feet long? (Sec. 22, Par. 4)

32. What factor determines the frequency ofdraining moisture from the compressor air filter?(Sec. 22, Par. 8)

33. What type of controller would you install if youwanted a steam valve to open on a decrease intemperature? (Sec. 22, Par. 17)

34. How do you clean the contact points on athermostat? (Sec. 22, Par. 23)

35. Under normal conditions, how dose to the setpoint will a humidistat control the humidity ofthe conditioned air? (Sec. 22, Par. 25)

36. Which type of controller is used to measure,record, and control humidity? (Sec. 22, Par. 27)

37. The piston type damper operator is at its normalposition. The control line pressure is 3 p.s.i.g.Why hasn't the operator begun to open thedamper? (Sec. 22, Par. 34)

38. What determines the operating range of apositioner used for damper operation? (Sec. 22,Par. 39)

39. After overhauling a damper operator, you noticethat it is operating erratically. What has causedthis erratic operation? (Sec. 22, Par. 43)

40. The pen on a recorder chart is skipping on thechart. What should you do to correct this fault?(Sec. 22, Par. 48)

41. When is it necessary to install a condensate loopon a pressure transmitter? (Sec. 22, Par. 57)

42. The recorder you are going to install has beenremoved from a cannibalized building. The penis full of dried ink. How should you clean thepen? (Sec. 22, Par. 64)

43. The system fan is off and the dampers aredosed. The fan switch is in the ON position.What caused the system to shut down and howwould you restart it? (Sec. 22, Pars. 73, 75, and76)

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44. How can you check the operation of an air-flowdetector? (Sec. 22, Par. 82)

45. Why is a graphic panel an asset in an air-conditioning system? (Sec. 23, Par. 1)

46. On graphic panels, temperature is alwaysindicated and recorded. (Sec. 23, Par. 2)

47. A malfunction is shown on a graphic panel.The component indicated on the panel is colorcoded green. What system is malfunctioning?(Sec. 23, Par. 4)

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CHAPTER 7

Evaporative Cooling

CAN YOU RECALL your days at the local swimmingpool or perhaps at the beach? If a slight wind wasblowing, you will remember that you were morecomfortable in the water than out of it. When youclimbed out of the pool, the water in your wet bathingsuit evaporated rapidly to leave your skin chilled from theloss of heat. Though you didn't give it much thought atthe time, you were really experiencing evaporativecooling.

2. Applying the same principle, our older surgeonsused an ether spray to freeze those portions of the skin inwhich incisions were to be made. Rapid evaporation ofthe ether reduced the temperature of the skin andunderlying flesh to the freezing point. You candemonstrate this principle for yourself by wetting yourhand with alcohol or water and holding it in theairstream from a fan.

24. Principle and Application of Evaporative Cooling1. In an evaporative cooler the air is drawn through

a finely divided water spray or a wet pad so that a portionof the water is being continually evaporated. The latentheat of evaporation, which must be passed on to thewater to evaporate it, is supplied from the heat of theincoming air, thus reducing the dry-bulb temperature, anincrease in the relative humidity and dewpointtemperature, and an unchanged wet-bulb temperature.

2. The water which is recirculated continuallythrough an evaporative cooler assumes the wet-bulbtemperature of the entering air after a short period ofoperation. The recirculated water will remain at the airwet-bulb temperature with no external heating or cooling.Makeup water is added to replace the evaporated water.

3. The temperature reduction, which can be madein the air passed through an evaporative cooler, dependsentirely on the wet-bulb temperature of the air which isto be cooled. The wet-bulb temperature of the airentering the evaporative cooler is at the lowesttemperature to which the circulating air may be cooled.

4. Evaporative cooling should not be used to coolair for spaces requiring constant temperature andhumidity control, such as hospital operating rooms andcertain types of highly technical electronic equipment.Evaporative cooling is best suited and chiefly used forcooling the space for the comfort of personnel.

5. Application. As we have shown, evaporativecooling depends on the evaporation of water; thus, it canbe successful only under atmospheric conditions of a lowrelative humidity. It can be used only where thedifference between the outdoor we-bulb and dry-bulbtemperature is relatively high. In the arid regions of thesouthwestern United States, where there is low relativehumidity, properly installed and operated evaporativecooling units cool comfortably. This type of systembrings in 100 percent outside air. It may be equippedwith a humidistat so that when the inside humidity ishigh and the cooler cannot function properly as anevaporative cooler, the water is cut off and the unit canoperate as a straight mechanical ventilating unit.Whenever the outdoor wt-bulb temperature is 73° F. orlower, effective cooling and indoor comfort can bemaintained by evaporative cooling.

6. The leaving air temperature of an evaporativecooler usually is just short of saturation; that is, the dry-bulb temperature of the air leaving a cooler does notquite reach the wet-bulb temperature of the air enteringthe cooler. An evaporative cooler operating at 90 percentefficiency will cool the air a number of degrees equal to90 percent of its original wet-bulb depression. Themeasurement of the approach to the entering wet-bulbtemperature is the saturation efficiency of the cooler. Airentering at 95° dry-bulb and 75° wet-bulb will be cooledto 77° if the cooler is operating at90 percent efficiency.Computation: The depression amounts to 950 (dry-bulbtemperature) minus 75° (wet-bulb temperature), or 20°.Ninety percent of 20 is 18. Subtract 18 from 95° (thedry-bulb temperature) and you have 77?, which is thetemperature to which the air is cooled.

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Figure 71. Evaporator cooler.

7. Components of Evaporative Cooling Units.Components of evaporative cooling units are very muchthe same in each type except that some have a differentmethod of supplying the water to the evaporating pads.

8. Drip units. Typical drip type evaporative coolercomponents consist of the following: a motor-driven fan,or blower; a circulating water pump, piping, and waterdistributors; a water collecting pan with water makeupfloat valve and drain; and water evaporating surfaces. Allthese components are assembled in a weatherproofcabinet, the complete assembly being known as a self-contained unit. It will range in size from the small, one-room cooler with a capacity of about 700 cubic feet perminute (c.f.m.) to the large industrial coolers withcapacities up to about 30,000 c.f.m.

9. The small, one-room cooler normally uses apropeller fan; the larger coolers use a squirrel-cage orcentrifugal blower. The propeller fan cooler dischargesthe cooled air directly into the conditioned space fromthe vaned air-discharge outlet of the unit. Duct work forair distribution is never attached to this type of unit.

10. Coolers of 2000-c.f.m. capacity and above usethe squirrel-cage blowers which are driven by a motorwith a V-pulley and a V-belt. Figure 71 illustrates thistype. Electric motors vary in size according to the size ofthe fan blade or blower:

11. The recirculating water pump is a vertical-shaft,directly connected unit of light construction. The pump

impeller is suspended in the pump housing from a ball-bearing motor shaft, which eliminates pump bearings andpacking. The pump housing has a wire-mesh screenthrough which the water passes as it is drawn in by thepump impeller and forced through the discharge tube tothe distributor. Pumps sit in the water of the collectingpan or are sometimes mounted on a special frame. Ineither case, they must be insulated to prevent vibrationand transmission of noise. Figure 72 illustrates this typeof water pump and its breakdown.

12. A water distributor is a trough which receivesthe water from the recirculating water pump through thedistributor head and distributes it evenly over the top ofthe evaporating surface pads. One distributor is providedfor each pad in the cooler. The water flows throughweirs (triangular openings) of the trough onto the padswhich are on the air inlet sides of the cooler. (See fig.73.)

13. The piping system consists of a T-fitting or awater distributor head with one inlet and three outletswhich are connected by pipe or tubing to the waterdistributors. The inlet connection from the pump isusually a rubber hose. In figure 74 you can see that thequantity of water which flows to the branch pipingsystem is regulated by an adjustable hose clamp whichthrottles the flow of water in the hose connecting thewater pump to the water branch tubes. The quantity ofwater which flows through the branch tubes to thetroughs is equalized by rubber or metal metering ringsplaced in each branch tube.

14. The water collecting pan forms the bottom ofthe cooler and contains the water, the water float makeupvalve, and water drain standpipe, as shown in figure 75.The makeup valve controls the level of the water in thecollecting pan and automatically admits water to replaceany that is lost through evaporation and bleedoff.

15. Water in the collecting pan should be kept at adepth sufficient to keep the recirculating pump primed.The overflow pipe consists of a removable length of pipe,the top of which is slightly below the top edge of thecollecting pan. When the water level in the collectingpan rises to the top of the overflow pipe, the excess waterflows into the pipe and is carried away to a drain.

16. Some drip type evaporative coolers (the oldermodels and the small, one-room type) are not equippedwith a recirculating water pump or troughs. In thesecoolers the water is supplied directly to the distributors.In this case the distributors are usually copper tubes withsmall holes drilled about I inch apart in order to give aneven distribution of water over the top edge of theevaporating pads. The flow of water is controlled by awater valve mounted on the inside of the front panel.Other models, in order to control

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Figure 72. Breakdown of water pump.

the flow of water, use an electric solenoid water valvewhich opens and closes when the cooler is turned on andoff. In this case the quantity of water also is regulated byan adjustable hose clamp on the hose feeding water tothe distributor header and by metering rings in thebranch pipes or tubes. Many coolers of this type havebeen installed in the past on military bases; however,present military design criteria do not permit installationof a drip type cooler that does not have a recirculatingwater pump.

17. The water evaporative surface of drip typeevaporative coolers consists of one or more pads of aspenwood excelsior, redwood excelsior, a mixture of redwoodand aspen wood excelsior, glass wool, or a fiber made of

other materials. The bulb excelsior is inserted in eithercheesecloth, hardware cloth, or a metal frame to bindand hold the material together in pads. The pads areheld in place by a barbed rack or other suitable means.Each pad is placed in a louvered frame, as you can see infigure 76. The louvered frames are fitted into openingson two sides and on the back of the cooler throughwhich the air is drawn by the fan. The louvers serve adouble purpose: they help to distribute the air uniformlyover the entire area of the water evaporating pads, andthey prevent water from wetting the area surrounding thecooler.

18. Spray units. Spray units (sometimes called

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Figure 73. Weirs.

air washer units) are made in sizes ranging from 3500c.f.m. through 12,000 c.f.m. They are larger indimension and weigh considerably more than the driptype unit. They are designed to keep the pads free ofexcess dust and water solids for a longer period ofoperating time than are the drip type units. They usesprays to wet and contin-

Figure 74. Waterflow adjustment.

Figure 75. Water makeup valve and standpipe.

uously wash down the inlet side of the filter pads andpartially saturate the incoming air by direct contact as theair passes through the sprays.

19. There are two main types of spray designs usedby manufacturers, with essentially the same results.These are the "spray nozzle" and the "rotating disk"(sometimes called slinger), shown in figures 77 and 78.Both spray type units consist of the following principalcomponents: piping; water collecting pan with makeupfloat valve and drain; recirculating water pump;evaporative filter and eliminator pads; sprays, eithernozzle or spray disk; and a motor-driven blower-allassembled in a self-contained weatherproof cabinet.

20. The piping system consists of the supply line andpiping to the spray nozzle. The collecting pan forms apart of the bottom of the evaporative cooler cabinet,which contains the float-actuated water makeup valve anddrain. Since the float controls the water valve, it alsocontrols the level of the water in the collecting pan. Thespray disk, or wheel, assembly of the evaporative coolersupplies a continuous sheet of atomized water over theair inlet face of the evaporative filter pad. The spray diskcollecting pan is located below and in front of the centerof the filter pad. The water in the collecting pan issupplied to the disk, or wheel, by a water pump similar tothose used on drip type units. The centrifugal action ofthe rotating disk distributes the water evenly in alldirections in a vertical plane so that the resulting curtainof spray water falling over the entire inlet face of theevaporative filter pads washes down the air inlet side ofthe pads continuously.

21. The automatic flush valve consists of anelectrically operated solenoid valve and an electric timercombined in one unit. This valve flushes the water fromthe water collecting pan regularly and automatically. Thisaction helps to keep the

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Figure 76. Breakdown of side panel.

Figure 77. Spray nozzle evaporative cooler.

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Figure 78. Rotating disc evaporative cooler.

collecting pan clean. The solenoid valve is operated bymeans of a coil of wire wound on a soft iron spool whichforms an electric magnet. When the current flowsthrough the coil, the valve stem is lifted to open thevalve. When current is cut off, the valve is closed eitherby gravity or by a spring. The operating solenoid part ofthe valve is completely enclosed. The water drain iscontrolled by a plunger, and a diaphragm isolates theworking mechanism of the valve from the water. Thevalve assembly is also provided with an overflowconnection and a manual operating lever to completelydrain the water collecting pan.

22. The electric timer regulates the flushing actionof the solenoid valve. It consists of a 1-hour electrictimeclock which is adjustable from 0 to 2 1/2 minutesdrain time. The settling of the drain time will depend onthe dirt content of the air entering the cooler, the saltcontent of the water, and the resistance in the wasteplumbing.

23. The spray nozzle does the same things as a spraydisk. Nozzles are usually mounted in both a vertical anda horizontal position: the vertical nozzles are used forwashing (down the evaporative filter pads, and thehorizontal nozzles for forming a curtain of spray waterover the entire air inlet area. Water is supplied to thenozzles through the piping system by a centrifugal pumpof large capacity and heavy-duty construction, mounted inthe water collecting pan. Figure 79 illustrates this type of

water pump which is completely sealed. All recirculatingwater pumps have a screen of sonic type to preventparticles of dirt and foreign matter from getting into thewater piping system.

24. Evaporative filter pads and eliminator pads areusually made of fibers of various materials and aresupported by angle frames and heavy wire mesh.Normally, spray type evaporative coolers use a speciallytreated hygroscopic spun glass for filter pads. Thismaterial assists in holding the fibers in place and helpsthe water adhere to the surface. The evaporative filterpads form the water evaporating surface. The eliminatorpads remove the moisture from the cooler air after itleaves the evaporative filter pads and prevent waterdropsfrom being carried over into the fan and motor of thecooler unit.

25. Blower fans, known also as centrifugal fans, areused on spray type units. The fan and the motor whichdrives it are both equipped with grooved type pulleys andare connected with V-belts. The fan has a self-aligning,self-oiling bearing on each side of the impeller wheel.Blower fans are designed and rated for air delivery against1/4 -inch water gauge static pressure resistance at thedischarge outlet of the unit. If the static pressure isgreater than 1/4 inch, water gauge efficiency will be lost.Blower fans, depending on size, are normally used tosupply air through a duct system.

26. Rotary-Drum Evaporative Units. As the nameimplies, the rotary-drum evaporative cooling unit uses arotating drum, powered by a reduction gear and motor.Figure 80 illustrates a partly dissembled rotary-drum unit.Other principal components are the exterior air-filter unit,the rotor housing, the water tank and the float-actuatedwater makeup valve, an automatic flush valve, and amotor-driven fan or blower. All of these components aremounted in a metal weatherproof cabinet. The rotary-drum type evaporative coolers are usually made in sizesranging from 2500

Figure 70. Sealed water pump.

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Figure 80. Breakdown of rotary-drum evaporative cooler.

through 6000 c.f.m. Blowers and motors are designedthe same as for the drip type evaporative cooler units.

27. The rotor, which is driven by an electric motorat an approximate speed of 1 1/2 r.p.m., is cylindrical andconsists of alternate layers of corrugated and flat screenwound on a drum. It revolves in the rotor housing, thelower portion being constantly wet by its immersion inthe water tank of the housing. When in operation, therotor continuously exposes an evenly wetted surface tothe incoming air. The rotor housing contains therevolving rotor and supports the rotor bearings and theelectric gear motor. The lower portion of the rotorhousing forms the water tank. The float-actuated watermakeup valve controls the water level in the tank.

28. The automatic flush valve empties the waterfrom the tank automatically. This action, which helps tokeep the rotor and water tank clean, is repeated regularlyby an electrically operated solenoid valve. The operatingsolenoid of the valve is completely enclosed. The waterdrain is controlled by a plunger, and a diaphragm isolatesthe working mechanism of the valve from the water.The valve assembly is provided with an overflowconnection. A manually operated valve is also providedto completely drain the water tank.

29. The action of the solenoid valve is regulated byan electric timer, a 1-hour electric timeclock with contactsthat open and close according to the time limit for whichthe timer is designed. The setting of the drain time,usually adjustable

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from 0 to 2 1/2 minutes, is dependent on the amount ofdirt in the air that enters the cooler, the salt content ofthe water, and the resistance in the waste or drainplumbing.

30. The filters of the rotary-drum type evaporativecooler, called air filters, are usually of the impregnated,washable, metal type. The filter unit is located on the airintake side, where the air can be cleaned as it enters thecooler.

31. Slinger Type Evaporative Units. The slingertype unit may be constructed as a double unit. The metalweatherproof cabinet may contain two sets of theprincipal components, such as two sets of spray wheelassemblies. The blower, or fan, of the slinger typeevaporative cooler is the same as on the rotary-drum unit-a motor-driven centrifugal blower. It is driven by a V-belt connecting the blower and motor by means ofgrooved pulleys. The blower which is used to supply airthrough the duct system is designed and rated for airdelivery against V4 -inch water gauge static pressureresistance at the discharge outlet. It has two self-aligning,self-oiling bearings, one on each side of the blowerwheel. The electric motor operating the blower ismounted high in the metal cabinet to protect it from toomuch moisture.

32. The electric motor operating the spray wheel isscaled in a waterproof assembly with water-seal packingaround the shaft to the spray wheel. The spray wheelpicks up water from the collecting pan and distributes itin all directions in a vertical plane by the centrifugalaction of the rotating spray wheel. This action supplies acontinuous sheet of atomized water which is sprayed overthe air inlet side of the evaporative filter pad. As the airpasses through the water, dust and dirt are removed andthe air is partially cooled. This continuous sheet ofatomized water also continually washes the dirt from thepad. The water collecting pan, which is located belowand in front of the evaporative filter pad, forms a part ofthe bottom of the evaporative cooler cabinet. A float-actuated water makeup valve, which controls the level ofwater, is contained in the collecting pan.

33. The automatic flush valve assembly consists ofthe flush valve, which flushes the water from the watercollecting pan regularly and automatically; solenoid valve;and timer. The timer is electric and has an adjustabledrain-time setting which regulates the flow of current tothe solenoid valve. The solenoid valve operates the drainvalve. This assembly is very similar to the flush valveassembly used with the rotary-drum type evaporativecooler.

34. The evaporative and eliminator pads are usuallymade of various washable materials supported by angle

frames and heavy wire mesh. The fibers are impregnatedwith a hygroscopic material which not only helps to holdthe fibers in place but also treats the fibers so that waterwill adhere to their surface. The evaporative filter padsform the water filter and evaporating surface, and theeliminator pads remove moisture from the cooled air.The eliminator pads also prevent small drops of watertrapped in the air from being carried over into the fanand motor of the blower compartment.

35. The cabinets for slinger type evaporative coolersare usually constructed the same as those for other largetype evaporative coolers. Heavy-gauge galvanized steel isused to enclose the entire unit. The sides are removableto provide access to the interior.

25. Installation Procedures1. The size and style of the unit determine the

location and the type of structure required to support it.2. Locations. Units mounted in building windows

are of the small, propeller fan and blower types. Theseare light in weight and will not do damage to the buildingstructure.

3. The large, heavy, blower type units must bemounted on self-supporting platforms adjacent to, butindependent of, the building. In some cases--the airwasher type unit, for instance--it may be moreeconomical to mount the unit on a concrete platform.

4. The dimensions and operating weight of thecooler should be determined before starting constructionof the supporting structure or mounting platform. Awalkway with guard rails round the cooler will give you asafe working area. Each platform should also have aladder, built as part of the structure.

5. Never mount cooler units on the building roof.Each unit must be mounted on the platform so that it isrigid and level. In some cases this may require shims andthe bolting down of the unit. Every cooler manufacturerfurnishes mounting and installation instructions with eachtype of unit. You should understand these instructionsbefore installing the cooler.

6. Connections. The various connections requiredfor evaporative coolers must be installed as specified foreach cooler. Check the instructions and see that theproper size pipe, valves, switches, wire, and fuse boxes areinstalled. Only in this way can you be sure that theequipment will give the expected service.

7. Water supply and drain. The small, window typeevaporative cooler normally uses 1/4-inch copper tubingto carry the water supply. A 1/4-inch fitting is located onthe side of the sillcock valve which is installed on anyordinary 1/4-inch outside water valve (garden hose).

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8. Large units must have a water supply line of atleast 3/4-inch pipe or tubing. A globe shutoff valve isinstalled in the supply line on the inlet side to the unit.Coolers using a water solenoid valve instead of arecirculating pump should have a water strainer installedon the inlet side of the solenoid valve. A water faucetwith a hose bibb should be installed in the supply linenear each cooler. This is to be used in washing down theinterior of evaporative coolers immediately after heavyduststorms or when maintenance service is being done.

9. The water drain or was system for evaporativecoolers should be at least 1 1/4 inches in diameter toreduce drain stoppage. The drain system should beconnected to the sewer or to a street drainage system. Infreezing areas the water supply system should beinsulated against freezing, or the unit may be installed topermit the complete draining of the system.

10. Electric connection. Small propeller units (windowtype) are usually connected by inserting the electric cordplug into a convenient outlet. Thus they can be placed inor out of operation by a toggle switch on the front of theunit.

11. The larger units should be equipped with theirown fuses. Sometimes this may require a separate mainswitch and fuse box, depending on the powerrequirements of the unit. Pushbutton stations or toggleswitches are used to start and stop equipment operation.Other units may require two separate switches, one forthe water recirculating pump motor and one for theblower motor, hooked in series with one of the motorleads. This allows the unit to be used for ventilation.The larger units usually require magnetic starters andsometimes have pilot lights or other devices to indicatewhen and what part of the cooling unit is in operation.All switches, controls, pilot lights, and Indicators shouldbe mounted on a control panel located in a convenientplace. Each large evaporative cooler should have adisconnect switch mounted inside the unit to permitmaintenance personnel to control the unit operationwhile performing maintenance service.

12. Air Distribution and Supply Ducts. Duct workfor evaporative cooling systems is designed and installedin the same manner as that refrigerative air-conditioningsystems. There must be a properly sized supply duct andadequate exhaust outlets.

13. Supply ducts. The supply duct enters thebuilding below the roof bearing plate direct from a unitwhich is mounted on a structure platform. The ductmust be installed without cutting any structural membersof the building. A slide damper of air stop should beprovided for winter closure of the duct system.

14. When practical, corridor space should be used asa plenum for air distribution ducts. The plenum must beairtight except for supply outlet grilles. Air supply branchducts to rooms or spaces a located to provide an evendistribution of air. Branch ducts and multiple air outletsfrom the main duct usually have dampers or splitters tobalance the flow of air. When the system is checked andadjustments are made, the dampers or splitter should belocked in place so that unauthorized persons cannotreadjust them. Directional flow vanes are usuallyinstalled on the supply outlet so that air may be directedwhere required. Do not use wire mesh screens on supplyoutlets; they provide no means of directing the flow ofair.

15. Exhaust outlets. To have proper cool aircirculation throughout the various spaces and rooms of abuilding, each room must have a proper size exhaustoutlet leading to the outside of the building. Exhaustoutlets should have louvers or adjustable vents forregulating the circulation of air. Exhaust fans may beinstalled to insure positive air circulation through spaceswith high temperatures, such as messhalls and areasaround ranges.

16. If windows are used as exhaust outlets, theyshould be raised to a fixed position. Window stopsshould be installed to prevent personnel from raisingwindows in excess of 4 inches. Not less than 2 squarefeet of louvered exhaust openings should be provided foreach 1000 cubic feet of air delivered to a room or spacewhen such exhaust openings are used in lieu of raisedwindows. All doors should be kept dosed to maintain abalance of the airflow throughout the conditioned space.

17. Automatic Controls. Automatic controls arenot essential but are convenient. When automaticthermostat and humidity controls are used, they shouldbe checked for proper operation and also should beadjusted, set, and locked in position to preventreadjustment by the using organization.

18. A thermostat is used to prevent the temperaturefrom going below a predetermined value. Thethermostat controls the operation of the blower andwater pump by starting and stopping them when thetemperature in the cooled area is above or below thepredetermined thermostat setting (usually 80° F.).

19. In some areas the evaporative cooler will have ahumidistat to control the humidity of the space beingcooled. The humidistat when used, controls the startingand stopping of the water pump whenever the relativehumidity in the space being cooled is below or above thepredetermined humidistat setting (usually 55 percent).Usually these controls are not used together. In case they

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are, the thermostat is usually connected to operate theblower and the humidistat to control the water pump. Inany case, they are connected to permit a constant supplyof air by continuous operation of the blower, thus turningthe unit into a straight mechanical ventilation systemwhen atmospheric conditions prevent the unit fromfunctioning as an evaporative cooler.

20. Startup Checks and Adjustments. Thesuccessful functioning of evaporative air coolers dependsdirectly upon the manner in which they are operated.Normally, the using organization is responsible only forstarting and stopping evaporative air cooling units andsystems. The personnel of the using organization mustbe instructed thoroughly in the operation of electricalswitches, water valves, and other controls. They arecautioned not to start the blowers prior to starting thewater pumps after long shutdown periods.

21. Startup Procedures. When a new or inactiveevaporative air cooling unit is to be placed in service, youshould perform the startup services to prepare theequipment for operation. Before starting the equipment,you must inspect all parts, accessories, and units to seethat they are secure and correctly adjusted. Seasonalstartup is scheduled well ahead of the time the equipmentis to be used. This allows ample time for inspection andstartup services. During initial startup procedures, allsupply outlets, vanes, dampers, and splitters should beopened for normal airflow. Moist rags should be placedover the supply air outlets into each space being air-conditioned to catch the dust and construction dirt beforeit is discharged into the space where occupants are onduty.

22. The ratings of motor overload protection devicesshould be checked against the motor nameplate ampereratings. If the devices are oversize or undersize, thermalelements of the proper size should be installed.

23. An ammeter should be connected to the blowermotor circuit prior to starting the motor. Starting andrunning currents should be recorded when the blower isfirst operated, with all pads and filters dry and in place.If the running current is equal to or less than theoverload rating of the motor, then the motor will not beoverloaded under final load conditions.

24. Testing the unit with clean, dry pads assures youthat the unit can be operated subsequently without waterfor ventilating purposes, since pads are always in placewhen the unit is operating. If the running current is inexcess of the motor overload rating, you must determinethe cause. In many cases, overload is due to excessivefan speed. Correct this before continuing the operationof the motor. The fan speed should be reduced byadjusting the variable-pitch motor pulley or by reducing

the size of the motor pulley. Where this is impractical,the blower pulley size should be increased. You shoulduse pulleys of the correct size rather than attempt to cutdown the original ones. An ammeter should be used tocheck the starting and running currents of the pumpmotor after the water collecting tank has been filled andthe pump first operated. If the running current is inexcess of the motor overload rating, determine the causeand correct it before continuing the operation of thepump.

25. During the initial operation of the unit withwater on the pads or sprays, air delivery in the supplyducts should be determined by a velometer or othervelocity-indicating instrument. Take readings at asufficient number of cross-sectional spots in the samesection of the supply duct so that you can arrive at anaverage velocity reading. Multiply the average velocity bythe square-foot, cross-sectional area of the duct. Thiscomputation will give the quantity of airflow in cubic feetper minute. If the rate of air delivery approximates thedesigned capacity of the system, the unit should becontinued in operation. If the rate of air delivery isconsiderably in excess of design capacity, reduce the fanspeed. In such a case, the fan motor is usuallyoverloaded and the velocity of the air through the waterevaporating pads is excessive. If this is the case, drops ofwater may be carried over into the fan compartment andcause shorting of electrical circuits, motor "burnouts,"rapid deterioration of belts, and excessive rust andcorrosion. After balancing air distribution to all spaces bythe use of velocity indicating instruments, lock alldampers, splitters, and directional flow vanes in their finalposition in such a manner that tampering or readjustmentis impossible except by the maintenance personnel. Unitswhich operate at efficiencies below 80 percent requireadjustment to improve their performance.

26. Shutdown Services. When evaporative aircooling equipment is to remain idle for long periods oftime, you must perform the preventive maintenanceshutdown services. This service protects the equipment,conserves critical materials, and prepares the equipmentfor minimum startup service. All parts, accessories, andequipment are inspected to insure proper servicing forseasonal shutdown or standby condition.

27. The shutdown service for evaporative air coolingequipment depends upon its condition and the method ofstorage. Usually the coolers are drained and washed outwith water under pressure. If they are to remain attachedto the building, they should be protected from theweather by some type of cover. Normally these coolersshould be removed from the building, stored in a dryplace, and overhauled during the winter season. Thisprocedure puts the coolers in good

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condition for the next season's run. Having beenoverhauled, they should give very little trouble during thecooling season.

26. Preventive Maintenance and Inspections1. Definite procedures for the preventive

maintenance of refrigerating and air-conditioningequipment are necessary for efficient operation. Theobjectives of preventive maintenance are as follows: toprevent breakdown, to insure proper maintenance, toprovide immediate and adequate minor repairs and avoidmajor repairs, to control maintenance costs, to establishspecific personnel assignments, and to develop minimumbut adequate maintenance records and data.

2. Well-planned inspections and up-to-date andcorrect records are required for a successful preventive

maintenance program. Inspection is a key phase ofpreventive maintenance. It is a simple fact that whenminor deficiencies are overlooked, they can cause majorbreakdowns in the future. This eventually defeats anypreventive maintenance program. The responsibility ofdetection is the duty of all personnel assigned topreventive maintenance.

3. Servicing Components. Table 1 containsinstructions which will serve as guide procedures forinspecting and servicing the components of evaporativeair cooling equipment. It may be necessary tosupplement these instructions and procedures with themanufacturer's instructions where the equipment is notstandardized in design.

TABLE 1

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TABLE 1 Cont'd

4. Major Repairs. Major repairs and renovation ofevaporative air cooling units should be done during thewinter every year. At post where there are a great manyunits to maintain, the shop space should be sufficient topermit proper repair of the units. Smaller units can beremoved from their platforms and taken into the shop asself-contained units. Since large units are not readilymovable, their component parts should be removed tothe shop. All units should be dismantled every year,thoroughly overhauled, cleaned, and painted to preventrust. It is best that fans be dismantled and wheels andscrolls cleaned and painted. Both inside and outsidecasings, pad frames, eliminators, water makeup pans, andmetal structural parts should be cleaned and painted.Pads should be replaced as required. The best practice isto see that the water distributing system and the spraypump are dismantled and inspected for cleanliness orexcessive impeller wear. Badly worn impellers should bereplaced. All bearings on the fans, pumps, and motorsmust be cleaned, checked for wear, and replaced whennecessary. All the ball bearings should be repacked withgrease and the sleeve bearings lubricated with oil orgrease as necessary. It is approved practice that units,when repaired, be replaced on their stands and their airintake louvers suitably covered to prevent the pads andthe equipment from becoming dust laden.

Review Exercises

NOTE: The following exercise are study aids. Write youranswers in pencil in the space provided after each exercise.Use the blank pages to record other note on the chaptercontent. Immediately check your answers with the key at theend of the text. Do not submit your answers for grading.

1. Agree. Disagree. Evaporative cooling removesheat from the air to evaporate the water. (Sec.24, Par. 1)

2. With an evaporative cooler, the air can becooled to its __________________temperature. (Sec. 24, Par. 3)

3. List the following cities in order of the bestenvironment for evaporative cooling:New York, New York.New Orleans, Louisiana.Dallas, Texas.Phoenix, Arizona.(Sec. 24, Par. 5)

4. What would be the most probable cause of lowwater supply to the distributor in an evaporativecooler? (Sec. 24, Par. 11)

5. Which type of evaporative cooler would youinstall in a dusty area? (Sec. 24, Par. 18)

6. On spray type evaporative coolers that utilize aflush valve, what controls the frequency ofoperation? (Sec. 24, Par. 22)

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7. What maintenance Is required when waterdroplets are being blown into the room from aspray type evaporative cooler? (Sec. 24, Par. 24)

8. A small evaporative cooler is connected to abuilding using duct work. The duct workcontains four elbows and a diffuser. What mayhappen to the evaporative cooler? (Sec. 24, Par.25)

9. Which evaporative cooler would require a heavystructure to support it, the 3000 c.f.m. drip typeor 3000 c.f.m. rotary-drum type? (Sec. 25, Par.1)

10. The drain on an evaporative cooler is pluggingup regularly. How can you correct thiscondition? (Sec. 25, Par. 9)

11. A new evaporative cooler, drip type, is installedin the messhall. Two switches are included withthe unit. What function could these twoswitches serve and how are they connected?(Sec. 25, Par. 11)

12. You have just installed an evaporative cooler ina room. What size exhaust opening should beprovided to allow proper cool air circulation?(Sec. 25, Par. 15)

13. A complaint is submitted to the refrigerationshop about excessive noise from the evaporativecooler. You find that the window opposite thecooler is open 2" and the cooler is rated at 4500c.f.m. The window measures 2 1/2' x 5'. Howcan you correct the complaint? (Sec. 25, Par.16)

14. What precaution should you give to the userafter you have checked the cooler for seasonoperation? (Sec. 25, Par. 20)

15. The blower motor on an evaporative cooler hasburned out. How could this have beenprevented? (Sec. 25, Par. 22)

16. How can you reduce the speed of the blower inan evaporative cooler? (Sec. 25, Par. 24)

17. How many c.f.m. is being delivered from a 12"x 24" duct when the average velometer readingis 50 f.p.m.? (Sec. 25, Par. 25)

18. What service must you perform on the troughsand weirs of a drip type evaporative cooler? (Sec.26, Par. 3)

19. How is the water distribution system cleaned?(Sec. 26, Par. 3)

20. What size feeler gauge is used to adjust the axialclearance of the blower wheel? (Sec. 26, Par. 3)

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CHAPTER 8

Mechanical Ventilation

HAVE YOU EVER waved a paper in front of your faceon a warm day? This is one form of ventilation system.The air moving across your face helped the moisture(sweat) evaporate. This evaporation process removedheat from your body so that you felt a cooling sensation.

2. You will study various ventilation systems andtheir application. There are many factors which must beconsidered when you install a ventilation system. Thesefactors are discussed in this chapter.

27. Ventilation and Distribution1. When ventilating a room or building, the factors

to consider are the tightness of construction, the numberof occupants, and the kind of work being done.Whenever human beings work in close quarters, thegaseous products from respiration, the odors fromperspiration, and the heat radiated from the body shouldbe removed. All of these byproducts of human activitytend to reduce human efficiency.

2. Proper air distribution is essential in a ventilatingsystem. The system not only should deliver a definiteamount of air to a room but also should distribute itevenly. If this is not done, the occupants will beuncomfortable from drafts, stuffiness, and temperaturedifferences between the floor and ceiling.

3. For instance, in comfort ventilation, a corner orspot near a window will be noticeably hotter or coolerthan the rest of the room. Since individual comfort is, inthis case, the main purpose of ventilation, you are reallyinterested only in distributing the air over the floor areaof a room to a height of about 7 feet. Complete airdistribution is more important when removing fumes andvapors from a building or room. Poor air distributioncauses gas fumes and vapors to remain in various areas ofthe building and creates an explosion hazard. In all caseswhere air is exhausted from a space, replacement airmust be supplied.

4. Air Distribution Standards. Air from fans andduets is delivered to a room through grilles. The purpose

of a grille is to distribute the air evenly and silently,without creating drafts.

5. So that the people will not have a feeling ofstuffiness, there should be a slight movement of air at alltimes. An air movement of 25 to 35 feet per minute(f.p.m.) is most satisfactory, but air motions of 20 to 50f.p.m. will usually prove acceptable.

6. Grille manufacturers normally rate their grilles asfollows:

a. Quantity of air in cubic feet per minute (c.f.m.).b. Outlet velocity in f.p.m.c. Nominal grille size.d. Blow of air in feet. (By "blow" we mean the

horizontal and vertical distance a stream of air travelsfrom the grille until it slows to a maximum velocity of 50f.p.m.; see fig. 81.)

e. Drop of air in feet. (By "drop" we mean thevertical distance the lower edge of a horizontal projectedairstream drops between the grille and the end of theblow.)

7. Air Distribution Limiting Factors. A few ofthe air distribution limiting factors are discussed in thefollowing paragraphs.

8. Blow. The blow at a grille must be sufficient toproduce satisfactory conditions throughout theconditioned area. Overblowing results in drafts andunderblowing may cause improper air mixing. If coolingair is being supplied, the cool air may drop too fast topermit proper mixing with the warmer room air.Experience has shown that the blow should be aboutthree-fourths of the distance toward an outside wall orwindow. This distance should be modified if the roomheight or height of a beam is such that the drop willcause a draft over the people inside.

9. Drop. Place the grilles so that the airstream atthe end of the blow is not less than 6 feet above thefloor level. However, the airstream should not touch theceiling as this may cause a dirt streak on the ceiling.

10. Air motion. To achieve desirable air motion in abuilding or a room without exceeding velocity limits isone of the more critical air

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Figure 81. Blow and drop.

distribution problems. Some of the factors which are aptto cause the motion of the air to exceed desirable limitsare: (1) excessive air discharge velocities, (2) high numberof air changes per hour, (3) premature drop of cold airinto the conditioned space, and (4) overblowing of theair.

11. Temperature differential. Temperature differentialis an important factor affecting grille performance. Anair differential of 5° requires little concern, but adifferential of 50° requires considerable care in the properlocation and selection of grilles.

12. Dirt. Although the supply air may have beencarefully filtered, it still contains small dust particleswhich will settle on ceilings and walls. A good rule is tolocate the grille at least two widths below the ceiling andmake sure that the air does not shoot up. and hit theceiling during the blow.

13. Noise. Grille noise is usually caused by the airdischarge velocity and the grille size. To insure quietoperation, make sure that the manufacturer'srecommendations are not exceeded and that airdistribution over the grille is fairly even.

14. The next subject we will discuss is ventilatingfans. We will learn how to select a specific fan for aparticular application.

28. Ventilation Fans1. The devices used to produce airflow are referred

to as fans, blowers, exhausters, and propellers.2. Types of Fans. The fans used with ventilating

systems are divided into two groups, radial-flow and axial-flow.

3. Radial-flow fans. Radial-flow fans-morepopularly called centrifugal, blower, or squirrel-cage-areused when a considerable amount of duct work isinvolved. The principal feature which distinguishes onetype of centrifugal fan from another is the curvature ofthe blades. The main types are the forward curved blade,

the radial blade, and the backward curved blade. The tipof the forward curved blade inclines in the direction ofrotation, while the radial blade is straight, and the tip ofthe backward curved blade inclines in a direction oppositeto the rotation. The performance characteristics of eachfan depends, of course, on its type. For a given output,the forward curved blade is used for relatively low speedoperation. The radial blade is used for average speedoperation, while the backward curved blade is used forrelatively, high speed operation.

4. Axial-flow fans. The axial-flow fan is one inwhich the air flows in line with the impeller axis, withina cylinder or ring. These fans are divided into varioustypes. Among the more popular types are: the propeller,tube-axial, and vane-axial.

5. The old design of propeller fan, which consistsof a propeller wheel within a mounted ring or plate, willnot handle air against high resistance. It is not suited fora system with ducts, grilles, filters, etc. However, thepropeller fan can be used to remove air from areas to theoutside atmosphere without a duct.

6. Recently, fan manufacturers have developed aspecial type of propeller fan which can move largevolumes of air against considerable frictional resistance.This fan has a large hub and short adjustable blades. It ishighly efficient, but operates at high speeds. This highspeed operation causes noise. therefore it should be usedonly in applications 'where noise presents no problem.

7. The tube-axial fan consists of an axial-flowwheel within a cylinder. It is normally used againstappreciable frictional resistance.

8. The vane-axial fan is similar to the tube axialtype. It consists of an axial-flow fan within a cylinder,with guide vanes before or after the fan. The purpose ofthe guide vanes is to increase its efficiency. A fan of thistype is more often used against moderate frictionalresistance.

9. Fan Capacity. The most important factor toconsider when selecting a fan for a specific job is theproper capacity. Too often the fan is selected on thebasis of diameter only. However, to determine the fancapacity you must calculate the c.f.m. and the staticpressure. After you calculate the c.f.m. and staticpressure, select the fan on the basis of efficiency, noise,cost, and physical size. You can estimate fan efficiencyby dividing the power output by the power input. Totalefficiencies range from 50 to 65 percent in small propellerfans to nearly 80 percent in centrifugal fans. Fanmanufacturers publish data which will aid you in selectingthe correct fan size. The noise level of the fan is animportant factor which must be considered beforeselection. Office

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buildings require quieter operating fans than do industrialshops.

10. Computing fan capacity is quite simple. Youmust know what size fan will make a given number ofair changes in a room in an hour. Once you know thec.f.m. of air needed, you can select the fan capable ofdelivering that amount. Multiplying the dimensions(length X width X height) of a room by the air changesrequired per hour will give you the total quantity of air tobe moved per hour. Stating this as an equation, we cansay:

Q = CV60

where Q = quantity of air per minute (c.f.m.) C = air changes per hour V = volume of room in cubic feet60 = minutes/hour

11. Now suppose you want to find the fan capacityfor a room requiring 12 air changes per hour. Supposethe room is 100 feet by 25 feet by 14 feet. Substitutingin the formula,Q = 12 X 100 X 25 X 14 = 420,000 = 7,000 c.f.m.

60 60Therefore the fan capacity must be 7,000 c.f.m.

12. Fan Motors. Ventilating fans are usually drivenby electric motors. Small fans, especially those which areoperated at high speeds, are normally connected directlyto the motor shaft. Large fans and those which operateat lower speeds are connected to motors through pulleys.

13. When you select a fan motor, it should be onesize larger than is required for normal load conditions.This is necessary because larger volumes of air may berequired.

14. Some type of thermal switch should be providedin the air inlet duct to break the circuit to the motor inthe event of a fire. Thermal switches of this type areusually set to open the motor circuit whenever the inletair exceeds 135° F. Electric fan motors should also havemanual electric switches so that you can control theoperation of the motors when servicing them.

29. Air Ducts1. Air ducts are pipes used to carry and distribute

fresh air or exhaust air from a building or room. Ductsare usually constructed of galvanized sheet steel. Twotypes of ducts are round and rectangular. Round ductsrequire less metal to carry the same amount of air, butrectangular ducts are used in most installations because ofspace considerations.

2. The correct size of ducts to be installed may bedetermined by using various charts and formulas procuredfrom manufacturers of air-conditioning equipment.However, for all practical purposes, it should be the samesize as the outlet opening of the fan assembly.

3. Friction Losses in Ducts. When air flowsthrough a duct, it loses some of its pressure because offriction. The greater the amount of air flowing through aduct of a given size, the greater is the friction loss.Furthermore, the power needed to deliver a certainamount of air increases rapidly as the size of the ductdecreases. For this reason, ducts should be of sufficientsize to keep friction losses to a minimum. Friction lossesare usually computed by the use of formulas; however,charts procured from manufacturers may be used.

4. To measure the air velocity through a duct orgrille, the ventilating system must be in operation.Several different instruments may be used to measurethis velocity. These include the "Alnor" velometer andthe anemometer. The "Alnor" velometer is the one mostcommonly used. It is a convenient instrument for spotreadings and is adaptable to many uses. For example, itmeasures velocities within an enclosure or duct, and atgrilles. It is sufficiently accurate for all practical purposes.The anemometer is a propeller or revolving vaneinstrument which' is connected through a gear train to aset of recording dials. The dials indicate the linear feetof air passing the instrument in a unit length of time(feet per minute).

5. Duct Fire Dampers. Fire dampen are used assafety devices to shut off the airflow in supply andexhaust ducts in case of fire. To automatically shut offthe air, ducts may be equipped with dampers and fuselinks. These should be provided when recommended bythe National Board of Fire Underwriters.

6. Now that we have the air flowing through theduct, we must furnish some sort of outlet for it. Thiswill be the subject for our next discussion.

30. Air Outlets1. Air supply outlets are either of the wall or ceiling

types. A number of different kinds of each have beendeveloped. The type and kind required will depend uponthe air distribution system you are using and the physicallayout of the room or building.

2. Wall Outlets. Wall outlets are classifiedaccording to the type of openings. They are as follows:(1) perforated grilles, (2) vaned grilles, (3) registers, (4)slotted outlets, (5) ejector nozzles, and (6) wall diffusers.

3. Perforated grilles. Perforated grilles have a smallvane ratio and are not adjustable. They are generallyused where .the direction of the airflow is not controlled.Perforated grilles may also be used as return grilles.

4. Vaned grilles. Vaned grilles are either of thefixed or adjustable types. They may be used for wall,floor, and baseboard applications. The fixed type is usedwhere the direction of the airflow

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is not controlled, while the adjustable type is used wherethe proper control of the air is essential. Vaned grillesare widely used, since they may be installed eithervertically or horizontally. This permits a wide selectionof grilles to meet particular requirements.

5. Registers. Perforated grilles designed withdampers or an arrangement of adjustable louvers arecalled registers. These units have a poor air outletdistribution and, for this reason, have only a limited use.

6. Slotted outlets. These outlets may be procured ina number of different designs, perforated, slotted, or acombination of both. They are used frequently in a longnarrow room with a low ceiling. However, the airquantity and distribution must be carefully planned;changes after installation are difficult. The blow forthese outlets is less than for other types, therefore theycan be used where obstructions might prevent properdistribution by other grilles.

7. Ejector nozzles. Ejector nozzles consist of apressure reduction box, sound reduction box, anddiffuser. Ejector nozzles give a long blow. They areused in places where cooking, drying, freezing, etc., are inprocess. Because of noise limitations, they are not usedwhere comfort is the primary objective.

8. Wall diffusers. The design of wall diffusers issimilar to ceiling outlet diffusers, which we will discussnext.

9. Ceiling Outlets. Ceiling outlets mostcommonly used are of three types. These are as follows:(1) plaques, (2) ceiling diffusers, and (3) perforatedceilings and panels.

10. Plaques. Plaque outlets are of simple design.The plaque is a flat surface, such as a thin piece of boardor metal, constructed an inch or two below the opening.The air hits the board or plate and flows through theopening between the plate and the ceiling and outwardinto the room. The plaque outlet is not widely usedbecause the flow of air is difficult to control.

11. Ceiling diffusers. Ceiling diffusers are eitherround or rectangular shaped and are installed flush withthe ceiling, or parallel and below the ceiling.Performance of the different types varies according to theprinciple used. Some have no internal induction, buthasten external induction by supplying air in multiplelayers. Others have internal induction and distribute airover an entire half sphere.

12. Perforated ceiling and panels. In these types ofoutlets, the air is diffused through perforations. Thesepanels are neat in appearance and maintain a low rate ofair movement.

13. We'll discuss the location of these outlets andgrilles in the next section.

31. Location of Supply and Return Grilles1. A room having air supply grilles without return

grilles must have some type of opening into a corridor oradjoining room. This opening is required so that air canleave the conditioned room. If 3000 c.f.m. of air iscontinually supplied to a room, 3000 c.f.m. mustsomehow leave the room. Some of the air passes outthrough cracks or around the windows or doors if theroom has no return air register. This leakage, however, isnormally not sufficient; and a relief opening is needed toinsure that the air has a free exit path. The reliefopening acts in much the same way as any opening in arecirculation air duct, except that no fan is moving the airthrough it.

2. The term "envelope" is defined as the outerboundary of an airstream. The envelope of a supply grilleis a sharp beam similar to a beam from a searchlight.Some air from the stream discharged by the grille leavesthe envelope and mixes with the adjacent room air,causing eddy currents and air motion in the air next tothe envelope. The location of the return outlets mayaffect the pattern of the supply-air envelope in the planand elevation pattern.

3. Supply-air envelopes, as they appear in a planview, are determined by the type of grille selected.Different manufacturers offer grilles having different planview standard envelope patterns. The plan view envelopeis ordinarily called the deflection of the grille. Standarddeflections are available from manufacturers. Grilles arealso available with vertical vanes or bars adjustable eitherindividually or in groups of five or six vanes. With suchgrilles, adjustments may be made in the field afterinstallation to obtain any deflection desired. Fixeddeflection grilles cannot be tampered with andconsequently lack the flexibility of the adjustable type.Figure 82 illustrates an elevation (side view) of a roomhaving a high air-supply outlet and a low return opening.This arrangement insures that the conditioned air will beblown across the room above the breathing level, willdrop to the floor at the opposite wall, and will be slowlydrawn across the room at the breathing level to thereturn register. Figure 83 illustrates an incorrect locationfor a return outlet. It shows that the air in half the roomwould have little motion. If occupants were near thereturn grille, they would be covered with a blanket ofcold air. The cold air would not have an opportunity tomix with the warm room air.

4. Sometimes fresh air must be supplied fromoutlets located in the ceiling. Figure 84 illustrates anarrangement where the air supply grille is located in themiddle of the ceiling with a low return opening located inthe wall. This layout is satisfactory because the air willhe blown

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Figure 82. High supply outlet and low return.

across the room above the breathing level of theoccupant.

5. Figure 85 shows a common method of supplyingand returning air from one grille. This arrangement withthe air supply grille and return opening built into' thesame supply duct is unusual and not often used. It isinteresting, however, to note the airflow pattern. Theapparent "dead spot" near the floor is of little importance.

32. Ventilating Equipment Components andInstallation

1. When installing a ventilating system, you mustconsider several factors. First of all, for comfort, acertain number of air changes an hour are needed. Thisnumber varies according to the temperature and humidityof the region as well as the purpose for which thebuilding or room is intended. For instance, in setting upa ventilating system for a large messhall, you mustremember that the ventilating problems for the kitchenwill differ from those for the main dining room, eventhough the two are part of the same building. Because ofthe purpose of the room, removing heat, moisture, andodors are your main concern in the kitchen, while in thedining room your biggest item is supplying the properamount of air for the number of occupants. Moreover,in planning you must consider the temperature extremes

Figure 83. Incorrect installation of high supply outletand low return.

Figure 84. Ceiling supply outlet and returnat floor level.

and the humidity of the region. For example, generallyspeaking you can set up fairly comfortable surroundingsby supplying an air change of 8 to 10 times an hour.However, during hot weather, 20 to 30 complete airchanges are desirable in northern climates; and as manyas 60 may be needed in southern regions.

2. Obviously you cannot rigidly follow a set pattern,since each installation will carry its own particularproblems. However, each manufacturer has certainspecifications for the installation of his particularventilating equipment. These specifications may varyfrom those of other manufacturers. Also, the installationof identical equipment may vary due to location, sourceof power, local installation procedures, codes, regulations,etc.

3. When installing a ventilating system, you shouldconsult text books, ventilation guides and manuals, andmanufacturer's data and catalogs. These will be especiallyhelpful when you are determining the quantity of air thatmust be removed to carry away gases, fumes, dirt, heat,vapors, and other undesirable foreign matter. Re-

Figure 85. Supplying and returning air with one fixture.

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member, also, that you must comply with the safetypractices of the National Safety Council and the FireUnderwriter's Board.

4. Removal of Heat, Odors, and Gases. Themost common method used to remove heat, odors, andgases is by operation of propeller fans. The installationof fans in the attic will draw outside air into the buildingthrough the windows, doors, and other openings anddischarge the contaminated air through the attic to theatmosphere. Satisfactory ventilating effects are usuallyobtained by providing approximately 60 air changes perhour. The accepted procedure is to install one or twolarge capacity fans instead of many small ones. Where asingle fan is used, it should be installed as near to thecenter of the room as possible. In cases where manyfans are used, the total volume of air to be moved shouldbe divided among the fans in relation to their capacity.For instance, if four exhaust fans are required to ventilatea rectangular building, they should be installed in amanner to permit each fan to ventilate one-fourth of thebuilding.

5. The following paragraphs discuss variousstandards used for different applications.

6. Attics. Vertical and horizontal fans arefrequently used to ventilate attics. These units drawoutside air into the building through windows, doors, andother openings and discharge it through the attic to theoutside.

7. Dishwashing spaces. Dishwashing spaces, whenconstructed as a separate room, should be provided withan exhaust ventilation capable of producing 90 airchanges per hour. The capacity of the fan should bebased on the floor space measured to the bottom of thehood. If the dishwashing machine without a hood isinstalled in a separate room, not less than 60 air changesper hour should be provided for the entire room.

8. Kitchens. The ventilating equipment installed inlarge kitchens should be capable of supplying 20 airchanges per hour. Horizontal exhaust fans are generallyused in kitchens and are normally placed at ceiling level.Exhaust openings at the outside of the wall should beprovided with louvers to keep out the weather. A birdscreen (an ordinary window screen) should be placedbetween the fan and louvers to keep out birds andinsects.

9. Kitchen ranges or deep fryers should beequipped with ventilating hoods. The effectiveness ofthese hoods depends upon exhausting large quantities ofair in order to remove the vapors. These hoods shouldextend approximately 1 foot beyond the outside edges ofthe equipment they serve. The bottom tip of the hood isusually 6h feet to 7 feet above the floor. Hoods andexhaust ducts are usually constructed of galvanized sheet

or cement asbestos board. A double canopy hood isconstructed with an inner shell which forms an airpassage between the shell and the hood. The air inletextends completely around the perimeter of the hood andhas a 2- to 3-inch space between the bottom tip of thehood and the inner shell. Inner shells have openings atthe top for exhaust air from the center of the hood area.The fan selected for a single canopy hood should have acapacity of 200 c.f.m. per linear foot of hood perimeter,while the fan for a double canopy hood should have acapacity of 150 c.f.m. per linear foot.

10. Round ducts are normally used with hoods.They extend from the hood, through the ceiling and roof,and terminate with a weatherproof cap. The verticalpropeller fan is normally used in this application.

11. Fan guards must be installed on all fans toprotect personnel from accidental contact. Kitchenexhaust hoods and ducts should be installed at least 18inches away from the stove. Most kitchen range hoodshave grease filters. These filters should be cleanedweekly to reduce fire hazard. Fans and duct work shouldhave a sufficient number of access doors to permit easycleaning.

12. Dining area. The ventilating equipment installedin messhalls should be capable of 10 air changes perhour. The fans generally used are of the propeller type.They are installed in the wall at ceiling level. Theexhaust openings should be equipped with bird screens.Either wood or metal louvers should be installed over theopenings to keep out the weather. Automatic louvers arepreferable.

13. Laundries. The ventilating equipment installedin laundries should be capable of 30 air changes per hour.

14. Barracks. The ventilating equipment installed inbarracks should be capable of supplying fresh air at a rateof 15 c.f.m. for each occupant.

15. Offices. The ventilating equipment installed inoffices and other similar spaces should be. capable ofdelivering 10 c.f.m. per person.

16. Theaters and chapels. In windowless or crowdedenclosures (theaters and chapels) 10 c.f.m. per occupantis required. Another method of calculating thisrequirement is to provide 2 c.f.m. for each square footof floor area.

17. Removal of Hazardous Fumes and Vapors.The removal of hazardous fumes and vapors frombuildings or spaces is accomplished by the use of specialexplosion proof or spark proof ventilating fans andmotors. Fans and motors of this type are entirelyenclosed so that any electrical sparks from either unitcannot cause an explosion. The maximum conveyingvelocities for hazardous fumes and vapors areapproximately 2000 f.p.m.

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18. When installing a system for removinghazardous fumes and gases you must take care to locatethe exhaust fans so that the fumes and vapors arepositively removed and do not create a dangeroussituation by remaining in the building. Some hazardousfumes and vapors are lighter than air, while others areheavier. Consequently, the specific gravity of eachhazardous gas determines the location of the fan.Following are a number of gases and their specificgravity:

Type Gas Formula Specific GravityAcetylene C2H2 0.90Ammonia NH3 0.59Butane C4H10 2.01Carbon dioxide CO2 1.527Carbon monoxide CO 0.967Chlorine C12 2.49Hydrochloric acid HC1 1.26Nitric oxide NO 0939Sulphur dioxide SO2 2.263

19. If the specific gravity of the gas is less than one,the gas is lighter than air and will rise to the ceiling. Ifthe specific gravity is more than one, the gas is heavierthan air and sinks to the floor. The exhaust fan shouldalways be placed so that it removes the air as fast as thevapor is released. Some of the buildings and rooms inwhich hazardous fumes and vapors are generated aregarages, paint shops, refrigeration shops, battery shops,etc.

20. Garages. In garages where toxic and explosivegases cannot be ventilated by gravity, forced ventilationmust be used. The system should be capable of supplyingor exhausting a minimum of 1 c.f.m./square feet of floorspace. Carbon monoxide produced from the incompleteburning of gasoline is lighter than air. For this reason,the exhaust fans used to remove this gas must beinstalled at least 7 feet above the floor. Gasoline vaporsmust also be removed. Since these vapors are heavierthan air, they must be exhausted at floor level.

21. Paint shops. Paint shops should be providedwith both supply and exhaust ventilation that are capableof producing 20 air changes per hour. Horizontalpropeller fans are generally used and installed in the wallat a height of approximately 7 feet.

22. In paint shops and paint spray booths theelectrical circuits which operate the exhaust fan and theair compressor should be interconnected so that thecompressor can run only when the exhaust fan isoperating. Such a safety measure lessens the probabilityof personnel being overcome by paint fumes. It is alsodesirable for the ventilating system to operate for a shorttime after painting operations have ceased.

23. When installing an exhaust system for a paintshop or paint booth, some means must be provided tofilter the particles of paint out of the air as it is forcedthrough the exhaust grille and out of the building.

24. To filter out paint particles from the exhaustair, various types of filters and louvers may be installed atthe grille. If the paint shop is located in an isolated area,less rigid precautions need be taken.

25. Removal of Foreign Particles. Many shopsneed an exhaust system with & collector to gather up andhold material that might clutter up the area. With thissystem, the airflow must be sufficient to catch the dust,chips, metal filings, etc., as they are produced. Air ductsor exhaust pipes carry these materials through theexhauster to the collector. If the collector is not used,the system must be designed so that the exhaust will notcontaminate the fresh air which is reentering thebuilding.

26. A local exhaust system consists essentially offour parts: (1) hoods or partial enclosures, (2) air ducts,(3) a collector, and (4) an exhauster. Data pertaining tothe quantity of air that must be removed in order tocontrol hazards or nuisances is available, as well asinformation on the necessary entrance velocities to hoodshaving different sizes and shapes.

27. The size of air ducts depends on the amount ofair to be moved and on minimum and maximum airvelocities. The minimum velocity must be strong enoughto keep particles from settling in the ducts, while themaximum velocity is limited by noise. If quiet operationis necessary, the velocity should not exceed 1200 f.p.m.In carpentry or machine shops the system must pull airover the article being worked on and must carry off thedust or chips. The air velocity for this applicationdepends on the weight and size of the dust particles orchips. Fine, dry dust requires a velocity of approximately3000 f.p.m., while larger particles, heavy loads, and moistmaterials require air velocities up to 6000 f.p.m.

28. Fans are the most common type of exhauster.Propeller type fans prove satisfactory in low velocitysystems; but the centrifugal type fan is necessary for ahigh resistance, high velocity system.

29. Vertical Discharge Ventilating System. Avertical discharge ventilating system, shown in figure 86,is designed with a vertical discharge propeller fan. Thecomplete system is mounted on the ceiling joists in theattic of the building to be ventilated. With thisarrangement, air is drawn into the building through thedoors, windows, and other openings, then circulatedthrough the building and finally exhausted through thefan into the attic. From the attic the air is forced outinto the atmosphere through a ridge ventilator. Insteadof ridge ventilators, gables, roof monitors, cupolas, andother similar openings may be used.

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Figure 86. Vertical discharge ventilating tan.

Doors between the rooms on this system must remainopen or be louvered so that the air can circulatethroughout the building. By looking at figure 86, you willnotice that a bird screen is installed at the, exhaustopening of the ridge ventilator and another screen isinstalled over the air intake opening in the ceiling.

30. This ventilating system is also equipped with abatten door which, when closed, stops airflow throughthe attic. The construction of the fan crate is also shownin this installation. It is designed with a fan shroud,which makes the operation of the fan more efficient.

31. Sleeve bearing fans and motors without thrustbearings should not be used in conjunction with vertic2adischarge ventilating systems. Fans and motors used invertical discharge systems must be equipped with thrusttype ball bearings.

32. Vertical Discharge Ventilating Supply System.Buildings or rooms with high internal heat loads, such asauditoriums, classrooms, and laundries, frequently use avertical discharge ventilating supply system. In thissystem, large propeller type supply fans mounted fromthe ceiling blow the air down over the occupants. Airshould be drawn in from the outside through louvered

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Figure 87. Horizontal discharge fan.

monitors to the fan. Then, after passing over theoccupants, the air can be vented to the outside throughwindows and doors.

33. Horizontal Discharge Ventilating System.Horizontal discharge ventilating systems are usuallyinstalled in the outside wall of a building or in a roofmonitor, as shown in figure 87. Louvers which open andclose automatically are generally installed in the outsidewall. In a ventilating system of this type the air is drawnthrough the building in the same manner as with verticaldischarge fans previously discussed. However, the air isnot pushed through the attic openings as in the case ofvertical discharge fans. Instead, it is pulled through bysuction and then forced through the opening into theatmosphere.

34. Louvers. Louvers are generally used wheninstalling horizontal discharge exhaust fans in roofmonitors or roof gables. They can also be used toweatherproof horizontal exhaust openings. Fixed woodenlouvers, unless properly made, may restrict air movementor give insufficient protection against bad weather.Wood louvers set in the frame at a 60° angle and spacedso that 2 inches of the opening is left between thecrosspieces will keep out the rain. Figure 88 shows themajor dimensions and capacities of louver panelsconstructed from l-inch wood stock.

35. For structural reasons, do not construct louverlengths to exceed 5 feet. If the capacity requires greaterlength, use multiple sections.

36. Automatic louvers for use with horizontaldischarge ventilating systems can be procured from fanmanufacturers. Various methods are used to open andclose them. They may be actuated by an electric solenoidor a motor. When the fan is installed next to the louverpanel, the louvers are actuated by air pressure. Air

pressure produced by the fan forces the louvers open,which are hinged at the top of the louver frame. Whenthe fan stops, the force of gravity closes them. Theinstallation of metal louvers is simple. They are attachedto the exhaust opening by wood or sheet metal screws.

37. Fans. Fans installed in ceilings or roof must beinstalled without cutting any structural members of thebuilding. Ceiling and roof construction must bestrengthened to support the additional weight. Accessdoors to attics or fan enclosures must be provided -forinspection and maintenance purposes. You must useunpainted canvas or other flexible material to connectducts to fan outlets or inlets.

38. Fan drive motors should be protected by eitherbuilt-in or external thermal overload devices. A thermalswitch may be installed in the inlet airstream of a fan forthe purpose of stopping the fan in case of fire. Theseswitches are usually set to open the circuit to the fandrive motor when the inlet air exceeds 135° F.

39. Filters. Air filters should be installed in allsupply ventilating systems where dust or other foreignmatter may be harmful to the activities conducted in theventilated space. Special conditions may require the useof absorbents or electrical precipitators. Filters or dustcollectors may be required on exhaust systems in specialuses where the fan discharge would create anobjectionable condition in the immediate vicinity or area.

40. Ducts. Dusts used for ventilation are usuallyconstructed of galvanized sheet steel. Their constructionshould be as smooth as possible where the air passes overthe inner surfaces. Ducts should be airtight and rigidlyattached to reduce vibration.

41. When installing ducts for ventilating purposes,follow these suggested rules:

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Figure 88. Wood louver details.

a. Use smooth duct materials to decrease airfriction.

b. Avoid sharp turns.c. Pipe the air as directly as possible to the required

location.d. When a duct must be altered to go through an

opening or between structural members of a building,make the change as slight as possible.

33. Inspection and Maintenance of MechanicalVentilating Equipment1. The primary reason for inspections and

maintenance is to let us determine the operating

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condition of an item of equipment and :to correct anydiscrepancy which may be found. -These services shouldbe performed on equipment at periodic intervalsaccording to an inspection and maintenance schedule.You must maintain inspection and maintenance recordsfor all of the ventilating equipment. Inspections andmaintenance services should be scheduled to permit onlya minimum of interference with the using organization.

2. Major repairs of ventilating equipment should bedone during the winter season or when the equipment isnot in use. Regular inspections show us when certainitems of equipment are in need of major repairs.

3. Inspections and Maintenance Services.Definite procedures for inspection and maintenanceservices of ventilating systems are necessary if we are tohave efficient and safe operation. The followingparagraphs discuss these services in general. Theinstructions given here should serve as a guide forinspecting and maintaining all mechanical ventilatingequipment. It may be necessary to supplement theseprocedures with the manufacturer's instructions, since theequipment is not standardized in design and may requireslightly different maintenance. Whenever warranted, tilefrequencies of inspections and maintenance servicesshould be adjusted to meet local operating conditions.

4. Fan Assembly. Fans should be inspectedperiodically for proper operation, lubrication, andcleanliness. Fan blades must be properly aligned and freeto rotate within their housings. The pulleys on the fanshaft and the motor shaft can be checked for alignmentby using a straightedge. Loose pulleys must be tightened.

5. You must replace all defective fan blades. Dirtyfan blades will cause vibration; therefore they must becleaned. Fan blades may be cleaned by using a suitablecleaning solvent or detergent and clean rags. After youdo the cleaning, you must tighten all bolts, nuts, andscrews on the fan assembly.

6. The axial clearance of each centrifugal fan mustbe checked to insure that the fan wheel is not binding inthe scroll. The axial clearance may be adjusted byrelocating the position of the shaft thrust collar. Afterfinal adjustment, the total axial motion should beapproximately 1/32 of an inch. Also after finaladjustment, lock the thrust collar in place with the thrustcollar setscrew. Worn thrust washers must be replaced.

7. Inspect and lubricate fan drives in accordancewith manufacturer's instructions. If the drive unit for thefan has a direct flexible connection, inspect the couplingsperiodically for wear and alignment.

8. The inspection and lubrication of fan bearings,especially of continuously operated fans, should be

performed at regular intervals. The shaft sleeve bearingsof fans are lubricated with oil, while ball bearings arepacked with grease. The fan grease cups require fillingonce each year. Over lubrication will cause oil to dripfrom the bearing, which will result in unsightlycollections of oil and dirt.

9. Each fan should be disassembled and inspectedfor defects yearly. Clean the fan shaft bearings andcheck each bearing for wear. Replace any bearings whichare unserviceable. Clean and paint the interior andexterior of the fan housing, the fan wheel, and similaritems with rust resistive paint. Care should be takenwhen working on fan wheels, as they are statically anddynamically balanced.

10. Lubrication of motor sleeve bearings. Lubricatemotor sleeve type bearings to the proper level, preferablywhen the motors are at a stand-still rather than whenthey are running. This procedure will prevent any falseoil level indication. The oil level should be observed fora few seconds to determine that it is at the proper level.Use a good grade of oil to lubricate sleeve type bearings.

11. Cleaning ball bearings. Motors equipped withball bearings and which operate at 1800 revolutions perminute and lower should be cleaned and lubricatedyearly. Motors operating above 1800 r.p.m. should bedisassembled every 6 months. The bearings should becleaned with approved solvent and repacked with newgrease. You must be sure that no dirt and grit enter thebearing chambers. If the motor is provided with self-sealed prelubricated ball bearings, the manufacturer'srecommendations should be followed for cleaning andrelubricating procedures.

12. Cleaning sleeve type bearings. Before cleaning thebearings, you must drain the oil from the bearingchambers. Then flush the bearing chamber with anapproved solvent, allow sufficient time for the bearing todry, and refill the chamber with clean oil.

13. Duct Maintenance. Inspect duct periodicallyfor air leaks, cleanliness, and structural condition. Repairor replace the defective ducts or duct connections.Remove all accumulations of foreign matter on theinterior of the ducts. If applicable, inspect soundabsorbing and insulating material on the interior of theducts to determine that the materials are insulatedsecurely and adequately. Inspect the duct hangers andsupports and repair or replace as necessary.

14. All ducts should be cleaned annually. Protectivepaints should be applied to the air ducts to protect themfrom corrosion. One of the more effective protectivecoatings is red lead paint. Apply three coats of paint.The first coat should be a rust resistive type such as redlead paint;

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the second coat should also be a rust resistive paint buttinted to the desired color. Finally a chlorinated rubber-base paint is used for the finish coat, particularly wherethe presence of highly corrosive gases would injurestandard paints.

15. Hood Maintenance. Inspect all the hoods forthe following conditions: broken or cracked surfaces, poorconnections to exhaust ducts, and accumulations ofmaterial such as dust, dirt, or grease. Repair or replaceany defective hoods. Remove all accumulations offoreign matter by washing the hoods with hot water,steam, or an approved solvent You must include somemeasurement of relative airflow through the hoods.Static pressure or hood suction measurements will proveuseful during this check if data is available on air volumesand pressures at the time the exhaust system wasinstalled. A marked reduction in air suction can betraced to one or more of the following conditions: (1)reduced performance of the exhaust fan due to beltslippage or an accumulation of material on the fan wheelor in the fan housing, (2) incorrect direction of rotationof the exhaust fan, (3) reduced airflow caused bydefective exhaust piping, and (4) losses in suction due toadditional exhaust points being added to the system.Clean and/or paint hoods as necessary.

16. Filter Maintenance. When filters become dirtyand clogged, they increase the resistance to the passage ofthe airstream and thus reduce the efficiency of thesystem. Therefore, filters should be inspected andcleaned or replaced periodically. The frequency ofinspection and cleaning will depend on the- type ofsystem in which the filter is installed and on the type offilter. Usually, filters should be cleaned or renewed atleast every 2 or 3 months. However, if the ventilatingsystem is used moderately, the cleaning or renewaloperation may be reduced to once during a full season.Under dusty conditions the filters may require cleaning orrenewal weekly.

17. Viscous impingement filters. Viscous impingementfilters, throw-away type, should be discarded when theybecome dirty. However, certain types of viscousimpingement filters are designed to be cleaned andreused. Cleaning may be accomplished by using hotwater, steam, or a cleaning solution that will remove theadhesive coating. After the filters are washed, they shouldbe dried. To recoat the filters, dip them in an adhesivebath long enough to coat all of the surfaces. Thenremove the filters and allow them to drain forapproximately 10 to 12 hours. You should use theadhesive coating recommended by the manufacturer.

18. Special filter cleaning equipment, such aswashers and oilers, may be used to recondition these

filters. Dirty filter are placed into a three-stage washingmachine. The first operation removes loose dust and dirtby ordinary washing. Next, the filters are washed by ahot alkaline solution under pressure. After the filters arewashed in the alkaline solution they are rinsed with clearwater. The filters are now drained, dried, and immersedin a high-temperature filter adhesive bath. After thefilters are removed from the adhesive bath, they areplaced in a centrifuge where excessive adhesive liquidsare removed. The reconditioned filters are then installedin a ventilating system or stored in special storage racks.19. Grease filters. Grease filters are cleaned in hot soapywater, or by spraying them with hot water. Use apressure of approximately 20 pounds per square inch anddirect the spray at the outlet side of the filter. After thefilter is washed, place it in a vertical position and allow itto drain.

20. Electrical precipitators. Electrical precipitatorsmay be cleaned in place manually with a brush orautomatically by washing the plates with hot watersprayed from fixed or moving nozzles. Precipitatorswhich may be washed in place are provided with drainsto carry away the waste water. Before any cleaningoperation is performed, you must turn off the electricity.It is best to follow the manufacturer's instructions todetermine the exact method of cleaning and thefrequency of cleaning electrical precipitators.

21. V-Belts. Inspect V-belts for breaks, evidence ofwear, and proper tension. A belt is tensioned properly, ifit has a deflection of 1/2 inch midway between thepulleys. If a belt is too loose it will slip; while anexcessively tight belt will cause increased loads andpremature bearing wear. Multiple V-belts must have thesame tension; otherwise the tighter belt will carry most ofthe load and wear out sooner.

22. The recommended procedure for V-beltreplacement is (1) loosen the motor at its base and shiftit closer to the fan, (2) place the belt on the motor pulley,(3) slip it over the fan pulley, (4) align the pulleys andbelt, (5) adjust the belt tension, and (6) tighten the motormounting bolts in the V-groove of pulleys. V-belts mustfit; otherwise rapid wear, noise, and slipping will result.

23. Multiple V-belts are furnished in matched setsby manufacturers to insure uniformity of length andtension. If a V-belt in a multiple V-belt set needs to bereplaced, be sure to replace the entire set, even whensome of the old belts seem to be in good condition.

24. Louver Maintenance. Inspect louver assembliesperiodically to determine that they are intact and thatthey control the airflow properly. Replace or repair anyloose or defective louvers. Wooden louver assembliesshould be painted ap-

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proximately once each year. Check the freedom ofmovement of automatic louvers and correct anydeficiencies. Place winter enclosures in position at thebeginning of the winter season and remove them at thebeginning of the summer season.

Review Exercises

NOTE: The following exercises are study aids. Writeyour answers in pencil in the space provided after eachexercise. Use the blank pages to record other notes on thechapter content. Immediately check your answers with the keyat the end of the test. Do not submit your answers forgrading.

1. When is it important that complete airdistribution be accomplished? (Sec. 27, Par. 3)

2. What are two ways you could reduce excessivegrille noise? (Sec. 27, Par. 13)

3. Which type of fan is normally used in aventilating system with considerable duct work?(Sec. 28, Par. 3)

4. You are to select a fan for a room requiring 30air changes per hour. The size of the room is14 feet by 60 feet by 60 feet. What must the fancapacity be? (Sec. 28, Pars. 10 and 11)

5. If you needed to reduce the friction loss of anair duct, would you increase or decrease the sizeof the duct? (Sec. 29, Par. 3)

6. Why are duct fire dampers used in mechanicalventilation systems? (Sec. 28, Par. 5)

7. What type of grille should you select for an airoutlet located in the floor and the airflow mustbe controlled ? (Sec. 30, Pars. 2-7)

8. Which wall outlet is used for long narrowrooms? (Sec. 30, Par. 6)

9. What determines the pattern of the supply airenvelopes? (Sec. 31, Par. 3)

10. List several factors that must be consideredwhen preparing to install a ventilating system.(Sec. 32, Pars. 1-3)

11. Where should you install a fan in a room thatcontains carbon dioxide? (Sec. 32, Pars. 18 and19)

12. What safety measure could you add wheninstalling an exhaust fan in a paint spray booth?(Sec. 32, Par. 22)

13. What factors determine the desired air velocityin a ventilating exhaust system? (Sec. 32, Pars.26-28)

14. What would result from poorly constructed fixedwooden louvers? (Sec. 32, Pars. 34)

15. When is it necessary to install filters in theexhaust system? (Sec. 32, Par. 39)

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16. Dirt on the fan blades will have what effect onthe fan operation ? (Sec. 33, Par. 5)

17. What will result from the overlubrication of fanmotors and other ventilating equipment? (Sec.33, Par. 8)

18. What determines the frequency of cleaning anair filter? (Sec. 33, Par. 16)

19. What will excessively tight fan belts cause? (Sec.33, Par. 21)

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CHAPTER 9

Heat Pumps

AT THE conclusion of this chapter you will know whatheat pumps are and will understand their operatingprinciples. We will also discuss the different types ofheat pumps, their sources and sinks, heat storage, andpump components.

34. Performance1. The operating principle of the heat pump is that

of the heat-power thermodynamic cycle governing theconversion of mechanical energy to heat. It is derivedfrom the Second Law of Thermodynamics (Carnot'sPrinciple). The law states that the efficiency of athermodynamic engine is proportional to the amount ofheat transferred from the source of heat to thecondenser; and that heat passes only from a warmer to acolder body. However, Carnot's formula for figuring thecoefficient of performance (COP) cannot be applied to anactual system. It is used only on an ideal compressor,with an ideal refrigerant.

2. "Coefficient of performance (COP) " is a termused to express the ratio of output to input. We use theterm "coefficient" because in a refrigeration system theperformance will be greater than 100 percent. A simpleformula to express this is:

COP = outputinput

The actual coefficient of performance is the ratio ofrefrigeration effect to the actual work input. The workinput is figured in brake horsepower of the compressor.

Actual COP = refrigeration effectb.hp. X 2545

Using this formula on a refrigeration system, we mustknow the rated capacity of the compressor in B.t.u.'s(refrigeration effect) and the brake horsepower. The2545 is a constant used to convert b.hp. into B.t.u.'s.For example, you have a compressor rated at 500,000B.t.u.'s/hr. It is using R-12 in a 46° F. evaporator thathas a 12° F. superheat. The compressor’s dischargepressure corresponds to 110° F. Under these conditions

the brake horsepower is 42. You would figure the actualCOP as follows:

Actual COP = 500,000 = 500,000 = 4.67 to 142 X 2545 106,890

In this actual situation we have put in 106,890 B.t.u.'s andreceived 500,000 B.t.u.'s of refrigeration effect, a ratio ofmore than 4 1/2 to 1.

3. In figuring the coefficient of performance of aheat pump, we must include the heat equivalent of thecompressor. Thus we use the following formula:

Heat pump COP = refrigeration effect + work inputwork input

= refrigeration effect + b.hp. X 2545 b.hp. x 2545

We shall use the same rating of 500,000 B.t.u.'s/hr. If allthe other conditions are the same as in the previousproblem, the b.hp. will be 42. We can find the ratio bythe following method:

Heat pump COP = 500,000 + 42 X 254542 X 2545

= 500,000 + 106,890 106,890

= 606,890106,890

= 5.67 to 1The input of 1 B.t.u. has given us a higher output on theheat pump cycle.

4. The heating coefficient of performance (COP)of an installed heat pump is the ratio of useful heatingeffect to the heat equivalent of the total energy requiredto operate the system. If total energy input of allauxiliaries such as fans and pumps is not included, itshould be so stated.

5. Now we'll compare the economy of a heat pumpto an electrical resistance heater. We will use a 50,000-B.u/hr. electrical resistance heater in our example.3410 B.t.u./hr. = 1kw.-hr. (Kw.-hr. = kilowatt-hour)50,00 B.t.u./hr. = 14.6 kw.-hr.3410 B.t.u./hr.

6. At 3 cents per kw.-hr., the heat load would cost14.6 X .03 = $.438/hr. = $.438 X 24 or

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$10.50/day. The monthly electric bill would be $315.00.7. Actually, the cost is much less than this, as the

heat load of a house averages much less than 50,000B.t.u./hr. At this point we will introduce a newterm--'"degree day." Degree day is a unit based upontemperature difference and time. It is used in estimatingfuel consumption and in specifying the nominal heatingload of a building during winter months. For any 1 day,when the mean temperature is less than 65° F., thereexists as many degree days as there are Fahrenheitdegrees difference in temperature between the meantemperature for the day and 65° F. The average or meantemperature in our example is 35° F. over a 9-monthperiod. We will assume that we have 10,000 degree days.The heat load for 50,000 B.t.u./hr./70° F. temperaturedifference house would be: 50,000 or 714 B.t.u./

70degree F./hr. The heat load for 24 hours would be: 714X 24 = 17.136 B.t.u./degree day; 17,136

3410= 5.02 kw.-hr./degree day. 5.02 X .03 X 10,000 =$1506/seasonal cost for heating by electrical resistance.

8. The heat pump reduces this cost considerablybecause it uses electricity only to drive the compressor.The refrigeration cycle permits the condenser to releasethree or four times as much heat as it takes in electricalenergy to drive the compressor. This coefficient ofperformance means that 1 kw.-hr. of electrical energydriving the compressor can release not 3410 B.t.u./hr.,but 3410 X 3 or 10,230 B.t.u./hr.

9. You can increase the efficiency further by usinga warmer heat source than the outside air. Some heatsources you might use are well water, lake water, or earth.If you could find a well furnishing 60° F. water, thecoefficient of performance would be 4 or 5 and thisfactor would bring the cost of operation close to that ofthe oil or gas heating system.

10. The term "performance factor" is similar tocoefficient of performance but is used when referring tovalues based on an extended period of performance. Theperiod of time covered would be given when using thisterm. If supplemental heat is involved, its effect shouldalso be specified.

35. Types of Heat Pumps1. Heat pumps a classified according to the type of

heat source and sink, heating and cooling distributionfluids, thermodynamic cycle, building structure, and sizeand configuration. We will discuss the more commontypes (shown in fig. 89) in the following paragraphs.

2. Air-to-Air (Refrigerant Changeover). This isthe more common type heat pump system.

Figure 89. Types of heat pumps.

Figure 89,A, shows the refrigerant flow. You will noticethat two expansion valves, two check valves, and achangeover valve are used to control the direction ofrefrigerant flow. The changeover valve (A), whichreceives a signal from a room thermostat, controls thefunction of the two heat exchanger coils.' The flow,when cooling is desired, is indicated with the plain arrow.Expansion valve C will act as the metering device for coilF and check valve D will allow the hot liquid refrigerantto pass into the receiver. When heating is desired(determined by the thermostat), the indoor coil F musttake on the function of a condenser

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and the outdoor coil G, the evaporator. Expansion valveB will act as the metering device and check valve E willallow flow to the receiver.

3. In small units, the expansion and check valvesmay be replaced with a capillary tube. A few installationshave been made in which the forced convection indoorcoil has been replaced by a radiant panel.

4. Air-to-Air (Air Changeover). The heat pumpcircuit shown in figure 89,B, is the air-to-air (airchangeover) type. Changeover is accomplished withdampers which control the flow of air across the twoheat exchanger coils. Figure 89,B, shows the systemwhen heating is desired. The indoor air is passingthrough damper A, over coil I, and out damper E, whilethe outdoor air is passing through damper C, over coil J,and out damper G. During the cooling cycle, dampers A,C, E, and G are closed and dampers B, D, F, and H areopen? This arrangement permits outdoor air to passthrough damper B, over coil I, and out damper F. Theindoor air will now pass through damper D, over coil J,and out damper H.

5. The dampers may be electrically orpneumatically operated.

6. Water-to-Air (Refrigerant Changeover). Thisheat pump is illustrated in figure 89,C. The water-to-airheat pump uses water as a heat source and sink, and usesair to transmit heat to or from the conditioned space.The operation is similar to the air-to-air type (refrigerantchangeover).

7. During the cooling cycle, the refrigerant passesthrough the changeover valve A to heat exchanger G.Check valve D will permit flow to the receiver, andexpansion valve C will meter the flow to the coil F.When heating is desired, the changeover valve A willdivert the refrigerant flow to coil F. Check valve E willallow refrigerant to pass to the receiver, and expansionvalve B will meter the flow of refrigerant to heatexchanger G.

8. The coefficient of performance for this typeheat pump is higher than the air-to-air types.

9. Earth-to-Air (Refrigerant Changeover). Earth-to-air heat pumps employ direct expansion of therefrigerant in an embedded coil, as illustrated in figure89,D. They may also be of the indirect type which we'vediscussed under the water-to-air type.

10. The operation of this system is identical to theair-to-air (refrigerant changeover) type except that theoutdoor coil is embedded in the ground.

11. Water-to-Water (Water Changeover). Thistype heat pump uses water for the heat source and sinkfor both heating and cooling operation. Changeover maybe accomplished in the refrigerant circuit, but in many

installations it is more convenient to perform thechangeover with valves, as illustrated in figure 89,E.

12. Valves A, B, C, and D are controlled by a roomor space thermostat. When the thermostat senses thatcooling is needed, valve (A) will allow the water to passthrough the condenser and discharge it out valve D. Thereturn water will flow through valve (B) to the chiller andback to the supply through valve (D).

13. During the heat cycle, the valves will bepositioned to permit water to pass through valve A to thechiller and then discharge through valve C. The returnwater will flow through valve B to the condenser. Fromthe condenser it will flow through valve D to the supplyinlet of the coil.

14. An earth-to-air heat pump (not shown in fig.89) may be like the earth-to-air type shown, except forthe substitution of a refrigerant-water heat exchanger forthe finned coil shown on the indoor side. It may alsotake a form similar to the water-to-water system when asecondary-fluid ground coil is used.

15. Some heat pumps which use earth as the heatsource and sink are essentially of the water-to-air type.An antifreeze solution is pumped through a loopcomprised of a pipe coil embedded in the earth and thechiller-condenser.

16. Other types of heat pumps, other than thoselisted, are possible. An example is one which uses solarenergy as a source of heat. Its refrigerant circuit mayresemble the water-to-air, air-to-air, or other types,depending on the form of solar collector and the meansof heating and cooling distribution which is employed.

17. Another variation is the use of more than oneheat source. Some heat pumps have utilized air as theprimary heat source, but are changed over to extract heatfrom another source (water earth, etc.) during peak loadperiods. When solar energy is used, another source mustbe used during periods of insufficient solar radiation.

36. Heat Sources and Sinks1. The more practical choice of heat source and

sink for a particular application will be influencedprimarily by geographic location, climatic conditions,initial cost, availability, and type of structure. A moredetailed discussion of design and selection factors foreach heat source and sink follows.

2. Air. Outdoor air offers a universal heat sourceand heat sink medium for the heat pump. Extended-surface forced convection heat exchanger coils areemployed to transfer the heat between the refrigerant andair. These surfaces are as much as twice the size of theindoor coil surface. The volume of outdoor air handledis also greater in about the same proportion. Thetemperature dif-

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Figure 90. Heat Pump component performance characteristics.

ference, during heating, between the outdoor air and therefrigerant is approximately 10°-25° F.

3. Selection. The two factors that you mustconsider when selecting a heat pump are the variation inoutdoor air temperature and the formation of frost. Asthe outdoor temperature decreases, the capacity of theheat pump (during heating operation). also decreases.Selecting a heat pump for a specific air temperature ismore critical than for a fuel-fired system. Care must beexercised to size the equipment for as low a balance pointas is practically possible for heating without havingexcessive and unnecessary cooling capacity during thesummer periods.

4. The procedure for finding this balance point(outdoor temperature at which the capacity matches theheating requirements) will be discussed in the followingparagraphs.

5. The performance characteristics of a heat pumpsystem can be estimated by evaluating and individual

components. Figure 90 illustrates the data thatmanufacturers make available with their heat pump.

6. The conditions of system balance can beestablished by the following procedure:

a. Choose a combination of evaporator refrigeranttemperature Tr and condensing temperature Tc.

b. Determine the compressor refrigerating effectfrom performance curves similar to those shown in figure90,A.

c. Determine the compressor power input (Pc) inkilowatts, as illustrated in figure 90,B.

d. Determine the condenser capacity fromQe = Qe + 3413 Pc - Qce

whereQc = condenser capacity (B.t.u./hr.)Qc = compressor refrigeration effect (evaporator

capacity)(B.t.u./hr.)Qce = heat loss from compressor to surrounding

air (B.t.u./hr.)Pc = power input (kw)

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Figure 91. Heat pump system balance.

e. Plot Qc obtained from step d on a chart similarto 90,C.

f. Select other condensing temperatures incombination with the original evaporator temperaturefrom step a and repeat steps b-e as necessary to determinethe condenser capacity at which the system balances.Points A and B on figure 91 represent the results of thesecalculations. Two points will normally be sufficient todetermine the balancing condenser capacity.

g. Select other evaporator temperatures and repeatsteps a-f.

h. For each evaporator find the corresponding heatsource temperature (Ta) from a chart similar to 90,D.

7. Once the conditions of system balance areknown, it is relatively easy to establish the heatingperformance characteristics. The net heating effect mayconsist of condenser heat, or depending upon the systemdesign, may also include heat losses from the compressor,motor, and refrigerant subcooler coil (if used).

8. For a heat pump which employs a constanttemperature heat source, a few computations willgenerally establish the balancing conditions for Tr andTc. A heat pump which uses a variable heat source suchas air requires a wide range of Tr to establish balancingconditions.

9. Figure 92 shows the performance characteristicsof a typical heat pump determined either from actualsystem tests or from an analytical procedure such aswe've discussed. Heating and cooling loads for typicalresidence are also shown in figure 92. If the balancepoint is above the heating design temperature (Td), thensupplemental heat will be required, as. shown by theshaded area in figure 92.

10. We've just. discussed one of the factors thatyou must consider when selecting a heat pump; now we'lldiscuss the other-frost formation.

11. When the surface temperature of an outdoor aircoil is 32° F. or lower, frost will form. Theaccumulation of frost will tend to reduce heat transfer,which reduces the capacity of the system. Research hasshown that with a nominal amount of frost deposit, theheat transfer capacity of the coil is not substantiallyaffected. The nominal amount is 2.5 pounds/square feetof coil face surface. The number of defrosting operationsrequired will be influenced by the (1) climate, (2) air-coildesign, and (3) hours of operation.

12. Experience has shown that little or no defrostingis required with temperatures below 20° F. and below 60percent relative humidity. However, under very humidconditions; when small suspended water droplets may bepresent in the air, the rate of defrost may be three timesas great as you would predict, using psychrometric theory.

13. Coil construction. The air-source heat pump usesthe extended or fin type coil. The external surface of thetube is known as the primary, and the fin surface is calledthe secondary. The primary surface consists of tubeswhich may be staggered, or placed in line with respect tothe heat flow. The staggered arrangement is preferredbecause it obtains a higher heat transfer value.

14. A more important factor in the performance ofextended surface coil is the bond between the tube andfin A firm contact between the tube

Figure 92. Heat pump operating characteristics.

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Figure 93. Condensing media flow.

and fin will insure free heat transfer from the fin to thetube.

15. Most coils are constructed of aluminum fins andcopper tubes, but copper fins on copper tubes are alsoused. Fin spacing varies from 8 to 14 per inch. The finspacing will be determined by the (1) duty to beperformed, (2) possibility of lint accumulation, and (3)consideration of frost accumulation.

16. Coil flow arrangements. In air-cooling coils theair usually flows at right angles to the tubes. In a one-row coil the direction of airflow would be at right anglesto the tube, but in multiple-row coils the airflow may becircuited, as shown in figure 93. Most dry expansioncoils use the counterflow circuit to secure the advantageof the highest possible mean temperature difference.Crossflow is also used, but is difficult to control becauseof the problem of equal parallel circuit loading.

17. Coil selection. The various factors you mustconsider when selection a coil are:

a. The duty requPb4 and de capacity needed tomaintain balance with other system components.

b. Temperature of entering air (D.B. and W.B.).c. Available cooling media and operating

temperatures.d. Space and size limitations.e. C.f.m. limitations.f. Allowable frictional resistances in air circuit and

cooling media piping system.g. Characteristics of individual coil designs.h. Installation requirements.-type of automatic

control etc.i. Coil air face velocity.

18. Coil ratings are based on a uniform facevelocity. Airflow interference, caused by air entrance atodd angles or by blocking a portion of the coil face, willaffect performance. To maintain the rated performanceof the coil, it is necessary that the air quantity (c.f.m.) beadjusted while the system is operated and kept at thisvalue.

19. You'll find that the more common causes ofairflow reduction are (1) dirty filters, (2) dirty coils, and(3) frost accumulation on the coil. You will avoid thesedifficulties if you implement a good preventivemaintenance program.

20. In the selection of coils, sufficient surface areamust be installed to transfer the total heat load from theair to the cooling media-refrigerant. This transfer mustoccur under the required temperature conditions andmaximum flow rates of both air and refrigerant. Thecoil total heat capacity must be in balance with thecapacity of related equipment, such as the compressor.Therefore, in making coil selections you will have toconsult manufacturer's rating tables or the manufacturer'slocal representative.

21. Heat transfer and airflow resistance. The rate ofheat transfer from the air to the refrigerant is affected bythree resistances. These three resistances are:

(1) From the air to the surface of the tube -usually external surface or air-film resistance.

(2) The resistance to the conduction of heatthrough the fin and tube metal.

(3) The resistance to the flow of heat betweenthe internal surface of the metal and the fluid in thetube.

22. The metal to heat conduction and the internaltube surface resistances are comparably low. Theresistance that you would be more interested in is theexternal surface or air-film resistance. You mayovercome this resistance by extending the coil surface bymeans of fins.

23. The transfer of sensible heat between thecooling medium and the airstream is influenced by

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(1) The temperature difference.(2) The design and surface arrangement of the

coil.(3) The velocity and character of the airstream.(4) The velocity and character of the medium

in the tubes.24. Water. Water is considered to be an ideal heat

source subject to the considerations listed below:(1) City water--availability, high operating

expense, scale formation on coils, and low temperatureduring the winter season.

(2) Well water-availability, original cost ofdrilling the well, composition of water (calcium,magnesium), and the life of the well (dry up).

(3) Surface water-availability, and it may containchlorides and micro-organisms (algae).

(4) Waste water-availability temperature, and itis very difficult to mass produce this type heat pump.

25. City water is not a good heat source because ofits nonavailability and its high operating cost. Well wateris particularly attractive from the standpoint of itsrelatively high and nearly constant temperature (50° F. innorthern areas and 60° F. or higher in the south). Youcan obtain information on well water availability,temperature, and chemical and physical analysis fromlocal U.S. Geological Survey offices. These offices arelocated in most major cities.

26. Utilization of water during cooling operationfollows the conventional practice with water-cooledcondensers. Water-refrigerant heat exchangers generallytake the form of either shell-and-coil or shell-and-tubetype direct-expansion water coolers. These heatexchangers are circuited to permit usage of the shell-and-coil or shell-and-tube as a refrigerant condenser duringthe heating cycle and as a refrigerant evaporator duringthe cooling cycle.

27. Earth. Heat transfer through buried coils hasnot been used extensively because of high installationcost, ground area requirements, and the uncertainty ofpredicting performance.

28. Compositions of soil vary quite widely (wet clayto sand) and affect the thermal properties and overallperformance.

29. Earth coils, usually arranged horizontally, aresubmerged 3 to 6 feet below the surface. A lower depthmay be preferred but excavation cost requires acompromise. The mean ground temperature for aspecific area generally follows the mean annual climatictemperature.

37. Heat Storage

1. The use of heat storage can improve theperformance of a heat pump. Installations of heat pumpswith heat storage have been made in large buildings.

2. We'll all have to agree that all materials possessthe property of heat storage. The structural materials ofa building are always in the process either of absorbingheat from or delivering heat to the interior space. Thiseffect is more pronounced in cooling operation wheregreater air temperature variation is tolerated. Heatstorage tends to reduce the rate of temperature changeand helps in some measure to reduce the peak loadrequirements.

3. A heat pump, with heat storage capabilities, canserve not only to reduce the size of a heat pumpnecessary for a given load but also to provide a moredesirable electric load. This may be done by shifting partof the load to the time of day when the cost of power isleast. Power is the cheapest during off-peak time. Theelectric hot water heater is a common example of such aheat storage application.

4. There are two types of heat storage systems thathave been employed: (1) sensible heat storage systems,and (2) latent heat storage systems. The latter is actuallya combination of the two. Heat storage, in the heatpump system, may be utilized on the high side when heatis available at a temperature suitable for direct heating. Itis used on the low side as an intermittent heat source attemperatures lower than the heated space.

38. Heat Pump Components1. The components used in heat pumps and the

practices followed bear a direct relationship to the airconditioner discussed earlier in this volume. In thissection we will discuss the component peculiar to thissystem-the reversing or change-over valve. Ourdiscussion will cover the operation and application of thevalve.

2. Operation. The 4-way reversing valve isoperated by a solenoid pilot 3-way valve which actuatesthe piston-operated main valve (reversing valve). Thepilot valve may be a separate component or an internalpart of the main valve. The pilot valve directs theactuating pressures-compressor discharge and suction-tothe top of the main valve piston. Figures 94,A, and 94,B,illustrates a heat pump system, during both heating (B)and cooling (A) cycles, using a typical 4-way reversingvalve. You can see that the main valve is externallyoperated by a solenoid pilot 3-way valve: There are alsotwo thermostatic expansion valves and two check valvesused in the system.

3. Now we'll cover the cooling cycle (fig. 94,A).The pilot valve is energized, thus allowing compressorsuction pressure to the top of the main valve piston.This causes the main piston

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Figure 94. Heat pump system with 4-way reversing valve, solenoid pilot 3-way valve,two thermostatic expansion valves, and two check valves.

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to rise. With the main valve piston in this position, thecompressor discharge follows path D to C, while thesuction gas (from the evaporator to the compressor)follows path E to S.

4. During the heating cycle, shown in figure 94,B,the pilot valve is deenergized. This allows thecompressor discharge pressure to be admitted to the topof the main valve piston and to move the piston down.In this position the compressor discharge gas follows pathD to E, and the evaporator return pressure from C to S.

5. We can summarize our discussion of the twocycles by stating that by energizing and deenergizing thepilot valve, the direction of refrigerant flow is reversed.We can also conclude that the main valve piston is heldin position by the pressure drop across the closed valvepoppets.

6. Application. We've already covered oneapplication of the reversing valve; now we'll discuss twomore. They are shown in figures 95 and 96. Figure 95shows a system with one 4-way reversing valve, onesolenoid pilot 3-way valve, one thermostatic expansionvalve, and four check valves. The system shown infigure 96 uses a 3-way reversing valve, a 4-way reversingvalve, a solenoid pilot 3-way valve, and two thermostaticexpansion valves. This system allows refrigerant to flowin one direction in the heat exchanger coils, while theother systems allow flow in either direction.

7. It is imperative in the system shown in figure 96to provide positive free draining of the liquid refrigerantinto the top of the receiver from the bottom of the coilwhen the coil is used as a condenser. In addition, it maybe necessary to allow for drainage of liquid refrigerantfrom the condenser before reversing the 4-way valve. Ifcaution is not taken, the liquid refrigerant can enter thecompressor and cause serious damage.

8. When a water cooled condenser is used in thesystem, it is necessary to add additional control devices toprotect it against freezeup. Freezeup may occur duringthe heating cycle because the condenser is used as a heatsource (evaporator). Two methods of protection areshown in figures 97 and 98.

9. Figure 97 shows a system using an evaporatorpressure regulator (EPR), connected to the condenser.The EPR is used to prevent freezeup of the waterflowing through the condenser during the heat cycle.When the system is returned to the cooling cycle, theEPR valve must be bypassed by a check valve which willallow the hot gas to flow to the condenser. A solenoidwater valve must be used to bypass the condenser waterregulating valve during the heat cycle. This will permit afull flow of water through the condenser.

10. A constant pressure liquid expansion valve isused in the system shown in figure 98. It feeds liquidrefrigerant to the condenser when it is used as anevaporator during the heat cycle. The valve must beadjusted to prevent the suction pressure from fallingbelow the pressure corresponding to the refrigerantsaturation temperature 33° F. during the heat cycle.This valve must be bypassed with a check valve whichwill permit the condensed liquid refrigerant to flow to thereceiver during the cooling cycle. In addition, theconnection to the receiver, to which the valve isconnected, must have a dip tube (quill) to insure anadequate supply of liquid refrigerant to the valve. Asolenoid water valve must be- used to bypass thecondenser water regulating valve when the condenserserves as an evaporator. This is done to insure completeevaporation of all of the refrigerant being fed by theconstant pressure liquid expansion valve. Liquidrefrigerant must never be allowed to return to thecompressor.

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Figure 93. Heat pump system with 4-way reversing valve, solenoid pilot 3-way valve,thermostatic expansion valve, and four check valves.

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Figure 96. Heat pump system with 3-way reversing valve, 4-way reversing valve, solenoidpilot 3-way valve, and two thermostatic expansion valves.

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Figure 97. Reverse cycle for defrosting using a 4-way reversing valve and an evaporatorpressure regulating valve.

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Figure 98. Reverse cycle for defrosting using a 4-way reversing valve and a constantpressure liquid expansion valve.

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Review Exercises

NOTE: The following exercises are study aids. Writeyour answers in pencil in the space provided after eachexercise. Use the blank pages to record other notes on thechapter content. Immediately check your answers with the keyat the end of the test. Do not submit your answers forgrading.

1. What is the COP of a refrigeration cycle whenthe refrigeration effect is 300,000 B.t.u.’s and thebrake horsepower is 40? (Sec. 34, Par. 2)

2. How much would it cost to operate a 100,000B.t.u./hr. electrical resistance hear for 1 day?The cost of electricity is 2 a kilowatt-hour. (Sec.34, Pars. 5 and 6)

3. How many degree days would you have if theaverage temperature for a 90-day period is 5° F.?(Sec. 34, Par. 7)

4. Why is a hat pump less expensive to operatethan an electric resistance heater? (Sec. 34, Par.8)

5. Which type of heating system is the cheapest tooperate, the air-to-air heat pump or an oil firedheating system? (Sec. 34, Par. 9)

6. How many expansion devices does an air-to-air(refrigerant changeover) heat pump have? (Sec.35, Par. 2)

7. What is the maximum temperature of therefrigerant during the heating cycle when theoutside temperature is 50 F.? (Sec. 36, Par. 2)

8. Why is outdoor temperature an important factorin selecting a heat pump? (Sec. 36, Pars. 3-9)

9. Will 40 pounds of frost substantially affect a 5' x4' coil? (Sec. 36, Par. 11)

10. How many fins does a 4-foot coil contain? (Sec.36, Par. 15)

11. What are the most common causes of airflowreduction? (Sec. 36, Par. 19)

12. Why isn't city water considered a good heatsource? (Sec. 36, Par. 24)

13. Which water source is considered the best heatsource? Why? (Sec. 36, Par. 25)

14. Why is heat storage beneficial to a heat pump?(Sec. 37, Par. 2)

15. The heat pump is operating as an airconditioner. The room temperature falls belowthe thermostat setting, but the unit will notreverse its cycle. Which component has mostlikely malfunctioned? (Sec. 38, Par. 2)

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16. What occurs when the pilot valve is energized?(Sec. 38, Par. 3)

17. An open in the pilot valve solenoid will causethe heat pump to operate on the cycle. (Sec.38, Par. 4)

18. How can you prevent freezeup of a water-cooledcondenser during the heat cycle? (Sec. 38, Pars.9 and 10)

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Answers to Review Exercises

CHAPTER 1

1. The factor that determines the type of filter design youwould use is the degree of cleanliness required for theconditioned area. (Sec. 1, Par. 6)

2. The filter arrangement used in a duct system having avelocity of 500 f.p.m. is with the filtering mediumplaced on edge. (Sec. 1, Par. 10)

3. When the pressure drop through a duct system is 2p.s.i.g. the filters are dirty. (Sec. 1, Par. 13)

4. The traveling media filter requires the least amount ofattention because the media roll usually lasts 3 months.(Sec. 1, Par. 17)

5. The type of filter you should install is a moving curtainfilter because it is considered to be fail safe. When themedia runs out, an indication it given and the circuit tothe filter motor opens. (Sec. 1, Par. 19)

6. The surface area of a dry filter may be increased bypleating the filtering medium. (Sec. 1, Par. 22)

7. The initial resistance of the filter is higher than theresistance at which the fan will operate. This conditionwill cause the motor to overheat. (Sec. 1, Par. 26)

8. An ionizing filter handling 3800 c.f.m. of air willconsume 97 watts. (Sec. 1, Par. 31)

9. The cost of filter operation for 1 hour is $.1797 X 60 = 5820 watts5820 watts = 5.82 kilowatts5.82 X $ .03 = $.175

(Sec. 1, Par. 31 and Question 8)10. A dry-bulb temperature of 50° F. and a dewpoint

temperature of 50° F. is 100 percent relative humidity.This high humidity will impair the dielectric propertiesof the filter. (Sec. 1, Par. 36)

11. The most probable cause of an odor in an air-conditioning system is a wet, dirty cooling coil. (Sec. 2,Par. 2)

12. Air at 70° F. and 100 percent humidity is saturated.(Sec. 3, Par. 4)

13. 2000 c.f.m. can be handled effectively by a 5-toncooling coil. (Sec. 3, Par. 7)

14. The quality of a liquid absorbent is controlled by theautomatic regulation of cooling waterflow through acooling coil in the absorbent sump. (Sec. 3, Par. 12)

15. The air temperature should be within 1° to 5° of theabsorbent temperature. To lower the temperaturedifferential, more contact surface should be added or theabsorbent temperature should be lowered. (Sec. 3, Par.14)

16. The adsorption efficiency of a dynamic dehumidifierwith an entering moisture content of 25 grains and anadsorbed moisture content of 20 grains is 80 percent, or20 = 4 = .8 = 80

25 5percent. (Sec. 3, Par. 21)

17. The economy of desorption is 1200 watts and the cost it$ .30.

400 X 3 = 1200 watts1200 watts = 12 kilowatts12 X .025 = .30(Sec. 3, Par. 22)

18. To evaporate 9 pounds of water, 9450 B.t.u.'s must beadded to the water. 1050 X 9 = 9450 B.t.u.'s. (Sec. 3,Par. 28)

19. Adding moisture to the air with an atomizer humidifierwill not affect the wet-bulb temperature. (Sec. 3, Par.28)

20. A humidistat can be used to control a valve in thecompressed air line. As more air is allowed to passthrough the line, more moisture will escape into the air.(Sec. 3, Par. 32).

21. The maximum efficiency of the impact humidifier ascompared to the atomizer type is 50 percent. Theatomizer uses 100 percent of the water supplied to it,while the impact uses 20 to 50 percent. (Sec. 3, Par.37)

22. The rate of airflow is important because moreevaporation will occur in a given period of time with anincrease in c.f.m. (Sec. 3, Par. 38)

23. 100 B.t.u.'s added to a forced-evaporation humidifier perhour with an airflow rate of 20 pounds of dry air perhour will add 5 B.t.u.'s to each pound of dry air. (Sec.3, Par. 40)

24. To correct this condition-water droplets leaving thewasher-you could install a bypass duct and allow avelocity of 500 f.p.m. to pass through the washer. (Sec.3, Par. 44)

25. The pressure has increased because the eliminator plateshave become plugged. This condition can be preventedby installing flooding nozzles in the air washer. (Sec. 3,Par. 44)

CHAPTER 2

1. On a centigrade the thermometer 15.5° is equivalent to60° on a Fahrenheit thermometer:C = 5 (60 - 32);C = 5 x 28 ; C = 140;

9 9 1 9C = 15.55°

(Sec. 4, Par. 4)2. On a Fahrenheit thermometer 104° is equivalent to 40°

on a centigrade thermometer.F= 9 X 40 + 32; F = 360

5 5+ 32; F = 72 + 32; F = 104°.

(Sec. 4, Par. 4)3. It would require 3.8 B.t.u.’s to raise the temperature of 8

pounds of cast iron 4°. (B.t.u. = 0.119 X 8 X 4. B.t.u.= 0.119 X 32, B.t.u. = 3.8) (Sec. 4, Par. 6)

4. The term applied to the sum of sensible heat and latentheat is "total heat" (Sec. 4 Par. 8)

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5. The dry-bulb thermometer will always indicate a highertemperature than the wet-bulb thermometer except whenthe air is saturated; then they will both indicate thesame. (Sec. 4, Pars. 10 and 11)

6. After whirling a sling psychrometer with the wet-bulbthermometer wick dry, the psychrometer thermometerswould read the same. (Sec. 4, Par. 11; Sec. 5, Par. 3)

7. The difference in the dry-bulb thermometer reading andwet-bulb thermometer reading will become greater as therelative humidity decreased. (Sec. 4, Par. 11; and Sec.5, Par. 3)

8. In order to determine the relative humidity, the dry-bulband wet-bulb temperatures must be known. (Sec. 5, Par.3)

9. Distilled water should be used to set the wick of a wet-bulb thermometer to help prevent the clogging of thewick. (Sec. 5, Par. 6)

10. If the total pressure of an air-conditioning systemremains constant and the air ducts become partiallyclogged, the static pressure will increase to over-comethe added resistance and the velocity pressure willdecrease. (Sec. 6, Pars. 8-11)

11. If the total airflow pressure is equal to 20 inches ofwater and the static pressure is equal to 4 inches ofwater, the velocity pressure is equal to the total pressureminus the static pressure or 16 inches of water. (Sec. 6,Par. 11)

12. Yes, it is possible to determine static pressure with avelometer. The velometer indicates the velocity pressurewhich you would subtract from the total pressure to getthe static pressure. (Sec. 6, Pars. 11 and 19)

CHAPTER 3

1. In calculating the wall area you must subtract 16” fromthe length to find the inside wall area. The ceiling sitson top of the wall so that the height measurement is notaffected. The wall area is 126.67 square feet.10' = 120" height14'= 168" length168"- 16"= 152"120" X 152" = 18240 square inches18240 ÷ 144 = 126.67 square feet(Sec. 7, Par. 2)

2. You should tell the user to draw the drapes to helpeliminate solar heat gain and to start the unit earlier sothat it wouldn't work against a peak load condition.(Sec. 7, Pars. 5-8)

3. The heat load from occupants will affect humidity themost. (Sec. 7, Par. 11)

4. To remove the heat which is causing abnormal unitoperation, you should ventilate the area. (Sec. 8, Pars.4 and 6)

5. The efficiency that would be lost is 85 - 75 or 10percent. (Sec. 8. Par. 9)

6. Cork should be used to insulate a 40° F. storage room,because this particular application is not considered a firehazard area. (Sec. 9, Par. 5)

7. You should insulate the strainer with an asbestos pad orblanket to facilitate the cleaning of the strainer. (Sec. 9,Par. 8)

8. You should use fibrous glass dabs, because they have alow moisture-absorbing quality and offer no attraction toinsects, vermin, fungus growth, or fire. (Sec. 9, Par. 14)

9. The most probable cause of a 55° F. temperaturereduction is moisture in the insulation around the pipe.The evaporation of the moisture will cause a heat loss.(Sec. 9, Par. 18)

10. When you insulate a valve in a 2-inch pipeline theinsulation should be the same thickness as the pipe. Theinsulation usually consists entirely of insulating cement.(Sec. 9, Par. 20)

11. The solar radiation through a 20' x 40' brick Wall with a30° F. differential isQ = UA (t1 – T0)Q = .34 x 800 (30)Q = 272 x 30Q = 8160 B.t.u./hr.(Sec. 10, Pars. 10 and 13)

12. The gross area of the wall is 120 square feet. Thewindow area is 16 square feet.Glass = 1.13 X 16 X 22 = 397.76 B.t.u./hr.Brick = 120 - 16 = 104 sq. ft.104 X .34 X 22 = 777.48 B.t.u./hr.Total heat gain = 397.76 + 777.48 = 1175.24B.t.u./hr.(Sec. 10, Par. 13)

13. Human load will give off the most latent heat gain. (Sec.10, Par. 13)

14. To find the total cooling load, you must add 10 percentto the sensible load.Total load = 42,156 + 4,215.6 + 8,750 = 55,121.6B.t.u.(Sec. 10, Par. 14)

15. 57,150 B.t.u. (sensible)5,715 B.t.u. (safety factor)9,170 B.t.u. (latent)72,03572,035 total heat load.12,000 B.t.u. per ton of refrigeration.72,03512,000 = approximately 6 tons.(Sec. 10, Par. 14)

CHAPTER 4

1. Before you plug in an air-conditioning unit you shouldread the nameplate to check the power requirements ofthe air conditioner. (Sec. 11 , Par. 5)

2. When the round third prong is removed from an air-conditioning unit plug an ungrounded condition willexist. When the air-conditioning unit is not grounded, apossible electrical shock hazard also exists. (Sec. 11,Pars. 9, 10, and 16)

3. It is not permissible to connect a 9.5-ampere rated air-conditioner to a 15-ampere circuit when other equipmentare using the same circuit. The total load of the airconditioner shall not exceed 50 percent of the currentrating of the circuit if the circuit feeds other equipment.(Sec. II, Par. 12)

4. If you are to replace an air-conditioner compressor motorthat has burned out due to excessive overload, youshould also replace the motor overload protector. If theoverload protector was operating correctly, the motorwould not have burned out from an overload. (Sec. 11,Pars. 24 and 25)

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5. As the room air passes through the evaporator its heatis absorbed by the refrigerant. (Sec. 11, Par. 28)

6. The refrigerant gas temperature is raised at thecompressor above the outside air temperature. (Sec. 11,Par. 29)

7. The air filter, evaporator coils, and condenser coils willcollect dirt and thus restrict airflow which will result inreduced air-conditioning unit output. (Sec. 11 Par. 32)

8. Before you check a capacitor with an ohmmeter youshould discharge the capacitor. (Sec. 11, Par. 44)

9. If the ohmmeter indicates zero (no continuity) when youcheck an overload protector. the protector is defectiveand should be replaced. (Sec. 11, Par. 46)

10. A low wattage draw is an indication of a low refrigerantcharge. (Sec. 11, Par. 51)

11. The two major causes of poor performance of an airconditioner are dirty filters and low voltage. (Sec. 11,Par. 62)

12. When using superheated steam to clean a condenser, besure that the temperature of the seam is not above themelting point of any of the materials from which thecondenser is constructed. (Sec. 12, Par. 7)

13. When mixing water and acid, always add the acid to thewater. If water is added to the acid, rapid heating willoccur which will cause the acid to spew from thecontainer. (Sec. 12, Par. 12)

14. If the water bleed tube of the evaporative condensershould become clogged, the formation of scale willincrease. The bleeding off of some of the recirculatedwater and replenishing it with makeup water willdecrease the amount of solids suspended in the coolingwater. (Sec. 12, Pars. 18 and 19)

15. Two of the conditions that would prevent thecompressor from unloading are; a broken spring in thehydraulic cylinder which moves the floating piston whenthe oil pressure is relieved or the oil pressure is notreleased from the valving mechanism hydraulic cylinder.There are several causes that would prevent the releaseof the oil pressure. Some of these causes are: defectivepressure-sensing device, broken mechanism that opensthe bleed orifice (item 9 in fig. 18), and a clogged bleedorifice (items 9 and 10 in fig. 18). (Sec. 12, Pars. 31-39)

16. The pan of the capacity control actuator that regulatesthe oil pressure to the compressor cylinder unloadermechanisms is the valving mechanism. (Sec. 12, Par.31)

17. Spring pressure in the cylinder unloader mechanism willhold the compressor suction valves open. (Sec. 12, Par.39)

18. The compressor must be loaded before adjusting theunloader system. (Sec. 12, Par. 41)

19. Before you install a solenoid valve, check the valve dataplate for the power requirements and the arrow on thevalve body for direction of liquid flow thru the valve.(Sec. 12, Par. 49)

20. Before you install a new solenoid valve in place of aburned out one, you should find the cause for theburned out coil. You should check the voltage of thepower source and the power requirements of the valve.Another possible cause could be high ambienttemperatures. Sec. 12. Par. 50

21. The two methods of varying the volume of the airhandled by an air conditioning system are by the use ofdampen or by varying the speed of the fans. (Sec. 12,Par. 56)

CHAPTER 5

1. Bypass dampeners are used to regulate airflow fromreturn ducts. (Sec. 13, Par. 2)

2. One probable cause of erratic damper operation isbinding blades. (Sec. 13, Par. 7)

3. The forward blade fan is most commonly used in a ductsystem. (Sec. 14, Par. 2)

4. The propeller, or disc, type fan should be installed in anarea requiring large amounts of exhaust air. (Sec. 14, Par.3)

5. The axial adjustment of the blower wheel isaccomplished by relocating the shaft thrust collar. (Sec.14, Par. 9)

6. Cooling coils are made of copper or aluminum becausethese metals readily conduct heat. (Sec. 15, Par. 1)

7. A 2-foot coil would contain 144 fins-24 X 6 = 144. (Sec.15, Par. 2)

8. You would straighten the fins with a special fin comb.(Sec. 15, Par. 4)

9. Brine solution is used in a system that requires a lowtemperature for dehumidification purposes. (Sec. 16,Par. 1)

10. The type of pressure loss caused by an elbow in the ductis dynamic loss. (Sec. 17, Par. 2)

11. The velocity reduction method of duct sizing is not usedbecause it does not take any account of the relativepressure losses in various branches. (Sec. 17, Par. 4)

12. A system with a velocity rating of 2400 f.p.m. isconsidered a high-velocity system. (Sec. 17, Par. 6)

13. Duct joints are sealed with compound, tape, or bywelding or soldering. (Sec. 17, Par. 9)

14. The type of duct materials you would use whencorrosive fumes are to be handled are copper, stain lesssteel, monel lead-coated or lead. (Sec. 17, Par. 12)

15. When air flows from a small chamber toward a largearea, the air tends to flow in a straight line. (Sec. 17,Par. 16)

16. The loss of cooling effect of a 12-sq. ft. duct having adifferential of 10° and a U-factor of 1.14 is 136.8B.t.u/hr.Q = UA (t1 – t0)Q = 1.14 x 12 x 10.Q = 136 B.t.u./hr.(Sec. 17, Par. 18)

17. Most duct air leakage occurs at transverse seams locatedagainst a wall or ceiling. (Sec. 17, Par. 22)

18. The amount of air required when the sensible hit load is49000 B.t.u./hr. and the temperature change is 15° F.is 3025 c. f. m.c.f.m. = 49000

1.08 X 15c.f.m. = 49000

16.2c.f.m. = 3025(Sec. 17, Par. 25)

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19. You can check the vertical flow from a grille by using alighted match, a warm thermometer, or alcohol on yourarm. (Sec. 17, Par. 34)

20. The horizontal airflow pattern is controlled by the rearfrets of the grille. (Sec. 17. Par. 34)

21. The baseboard type of diffuser is the hardest to use forbalancing because it has few adjustments. (Sec. 17, Par.38)

CHAPTER 6

1. The thermostatic expansion valve uses the vapor-tensionprinciple in its operation. (Sec. 18, Par. 6)

2. The control response a motor control uses is two-position. (Sec. 19, Par. 2)

3. To set a LPC for a wider differential you would turn theadjusting screw so that more force is exerted upon thebar. (Sec. 19, Par. 5)

4. The compressor will cut off at 25 p.s.i.4 0 p.s.i. - 15 p.s.i. = 25 p.s.i.

(Sec. 19, Par. 9)5. Since the system uses an automatic expansion valve, a

low-pressure motor control cannot be used to controlcompressor cycling. You must install a thermostaticmotor control and adjust it to the desired cutout and cut-in temperatures. (Sec. 19, Par. 10)

6. A broken feeler bulb on a thermostat will give the saleindication as a filed ice bin. (Sec. 19, Pars. 12-15)

7. The air conditioner is not running because the kinkedfeeler bulb acts as if a loss .of power element charge andwill not close the contacts in the TMC. To correct thiscondition, you must replace the power element or theentire TMC. (Sec. 19. Par. 20)

8. Snap action and mercury switches are used to preventcontrol failure due to arcing when the circuit is open orclosed. (Sec. 20, Par. 2)

9. A direct short is indicated when the ohmmeter readszero ohms resistance. (Sec. 20, Par. 7)

10. The mode of electric control you would use to operate arefrigeration unit is two-position because the unitrequires on-off operation. (Sec. 20, Par. 13)

11. The control point would be at any point between thetwo extremes because the control cycles the louversbetween the extremes and is never satisfied. (Sec. 20,Par. 18)

12. The timed two-position control responds to gradualchanges in the controlled variable, while the simple two-position control responds to one of two extremes. (Sec.20, Par. 24)

13. A heater is used to slow down the action of the bimetalelement. (Sec. 20, Pars. 31 and 32)

14. You should install a proportional response controlbecause system offset is minimized. (Sec. 20, Pars. 35-37)

15. Since lag time is not a problem, a simple two-positioncontrol, series 20, can be used. It is cheaper, easier tomaintain and calibrate, and safer because it operates atlow voltages. (Sec. 20, Par. 41)

16. The change in variable causes a bellows to expand andmake a circuit to the starting winding of the motor. The

motor is energized and begins to rotate clockwise. Afterit has rotated 180°, a cam operated switch will break thecircuit and stop the motor (Sec. 20, Pars. 43-46)

17. The series 40 control action is similar to a single-polesingle-throw switch. (Sec. 20, Par. 49)

18. No, you can't substitute it with anything but a series 60floating motor because it is revertible and the twoposition is not. (Sec. 20, Par. 55)

19. You cannot substitute a series 20 motor with a series 60because the 20 operates on low voltage, while the 60uses line voltage. (Sec. 20, Par. 58)

20. The amount of current flowing through the relay willaffect the position of the contact blade between the twomotor contacts which, in turn, controls the position ofthe controlled device. (Sec. 20, Pars. 66-68)

21. The series 90 motor will stop running when thebalancing relay is balanced. (Sec. 20, Par. 73)

22. The most probable cause of a damper remaining closedwhen the control calls for it to be open is loose locknuton the linkage to the damper shaft (Sec. 20, Pars. 79and 80)

23. The main difference between a series 90 humiditycontrol system and a series 90 temperature controlsystem is the sensing device which operates thecontroller wiper. (Sec. 20, Par. 18)

24. The humidistat is wired into the blue wire of the rightcircuit. (Sec. 20, Par. 93)

25. When one belt in a set breaks. you must replace thecomplete set because the remainder of the belts arestretched and the new belt will not have the propertension. (Sec. 21, Par. 3)

26. A compressor losing efficiency is usually caused bydefective air cleaner. (Sec. 21, Par. 4)

27. When the first stage is operating at normal and thesecond-stage pressure is zero, the pressure relief valve isstuck open. (Sec. 21, Par. 8)

28. Before you start a newly installed compressor, you mustcheck the oil level in the compressor crankcase (Sec. 21,Par, 15)

29. If you replace the standard head gasket with a thin headgasket, the compressor will probably knock (Sec. 21,Par. 21)

30. Supply-air lines are lines connecting the controllers tothe air source, and the control air lines connect thecontrollers to the controlled device. (Sec. 22, Par. 1)

31. You must allow a 1 1/2-inch pitch for a 12-foot supply-air header, 1/8 inch per foot of header.3 inches. 1/4 inch per foot. (Sec. 22, Par. 4)

32. The amount of moisture present in the air determine thefrequency of draining the filters. (Sec. 22, Par. 8)

33. You would install a reverse acting controller so that adecrease in temperature will cause an increase in airpressure to the valve. (Sec. 22. Par. 17)

34. You clean the contact points on a thermostat by drawinga piece of hard-finish paper between then (Sec. 22, Par.23)

35. Under normal conditions, a humidistat will control thehumidity within 1 percent R.H. of the set point (Sec.22, Pat. 25)

36. Hygrometers are the controllers used to measure, record,and control humidity. (Sec. 22, Par. 27)

136

37. The spring in the piston type damper operator usuallyfunctions between 5 and 10 p.s.i.g. At 3 p.s.i.g. thedamper should be at its normal position. (Sec. 22, Par.34)

38. The spring attached to the operator stem determines theoperating range of the positioner. (Sec. 22, Par. 39)

39. When you overhauled the operator you probably kinkedthe diaphragm, which would cause erratic operation ofthe damper operator (Sec. 22, Par. 43)

40. To correct a skipping pen, you must bend the pen armslightly toward the chart. The pen should rest on thechart lightly. (Sec. 22, Par. 48)

41. A condensate loop should be installed on a pressuretransmitter when it is used to measure the pressure of ahot, moist atmosphere. (Sec. 22, Par. 57)

42. The dried ink may be cleaned from the pen by washingit in warm water. (Sec. 22. Par. 64)

43. The fire protection control has malfunctioned or wasactivated and shut the system down. You should checkthe fire protection control, then reset it. (Sec. 22, Pars.73, 75, and 76)

44. You can check the operation of an airflow detector byblocking off a section of the filters or by closing adamper before the air reaches the instrument. (Sec. 22,Par. 82)

45. A graphic panel is an asset because you can monitor andcontrol the entire system from one central location.(Sec. 23, Par. 1)

46. On graphic panels, chill water temperature is alwaysindicated and recorded. (Sec. 23, Par. 2)

47. When a green coded component on the graphic panel ismalfunctioning you are having trouble with thecondensing water system. (Sec. 23, Par. 4)

CHAPTER 7

1. Disagree. Evaporative cooling changes sensible heat tolatent heat but doesn't affect the wet-bulb temperature(total heat). (Sec. 24, Par. 1)

2. With an evaporative cooler, the air can be cooled to itswet-bulb temperature. (Sec. 24, Par. 3)

3. Phoenix, Arizona, is first because it has a high averagedry-bulb temperature and low wet-bulb temperature.Dallas, Texas follows second and New York is third.New Orleans is fourth because its average dry-bulbtemperature is in the middle 90's and the wet-bulbtemperature in the mid 80,s. (Sec. 24, Par. 5)

4. The most probable cause of low water supply to thedistributor in an evaporative cooler is a plugged pumpintake screen. (Sec. 24, Par. 11)

5. The spray type evaporative cooler should be-installed ina dusty area because it keeps the pads free of dust for alonger period of time. (Sec. 24, Par. 18)

6. An electric timer controls the frequency of operation ofthe flush valve on spray type evaporative coolers. (Sec.24, Par. 22)

7. The eliminator pads must be placed when waterdroplets are carried in the air to the conditioned area.(Sec. 24, Par. 24)

8. Since centrifugal fans are rated for a delivery against1/4-inch water gauge static pressure, nothing would

happen unless the pressure exceeded ¼ inch. If itexceeded 1/4 inch the cooler would lose efficiency. (Sec.24, Par. 25)

9. The 3,000 c.f.m. rotary drum would require a heavystructure because of its sis and weight. (Sec. 25, Par. 1)

10. The drain should be 1 1/4 inch in diameter to reducestoppage. If stoppage occurs with a larger drain youmust flush, the cooler sump more often. (Sec. 25, Par.9)

11. The function of the two switches is to cont theoperation of the recirculating pump motor and theblower or fan motor. They are connected in series withone of the motor leads. This procedure allows thecooler to be used as a ventilation system. (Sec. 25, Par.11)

12. You must provide an opening large enough to exhaustall the air brought into the area by the evaporativecooler. The size of the opening is obtained from thecooler manufacturer or data books. (Sec. 25, Par. 15)

13. The exhaust opening is not sufficient (less than 1 squarefoot) and is causing noise. You must allow 9 sq. ft. oflouvered exhaust for a 4500 c.f.m. evaporative cooler.(Sec. 25, Par. 16)

14. You should caution the user not to start the blowerbefore the water pump. (Sec. 25, Par. 20)

15. The burned-out motor could have been prevented byinstalling a motor overload protective device in serieswith the motor lead. (Sec. 25, Par. 22)

16. You can reduce the spied by adjusting the motor pulleyor by reducing the size of the motor pulley? (Sec. 25,Par. 24)

17. 100 c.f.m. is delivered from a 12” X 24” duct with avelocity reading of 50 f.p.m.12” X 24” = 288 sq. in.288 sq. in. = 2 sq. ft.50 X 2 = 100 c.f.m.(Sec. 25, Par. 25)

18. The service that you must accomplish on troughs andweirs of a drip type evaporative cooler is cleaning,painting, or replacement. (Sec. 26, Par. 3)

19. The water distribution system is cleaned by flushing itwith a 10 percent solution of muriatic acid. (Sec. 26,Par. 3) 20. The axial clearance of the blower wheel is1/32” To adjust the clearance you would use a .030feeter gauge because 1/32” = .0313. (Sec. 26, Par. 3)

CHAPTER 8

1. Complete air distribution is important when hazardousvapors and fumes may exist in an area such as a batteryshop. (Sec. 27, Par. 3)

2. The two ways you could reduce grille noise are: changethe size of the grille or reduce the air discharge velocity.(Sec. 27, Par. 13)

3. The radial-flow fan is normally used in a ventilatingsystem which has considerable duct work. (Sec. 28, Par.3)

4. The fan capacity must be at least 1,260 c.f.m. for aroom 14 feet by 60 feet requiring 30

137

air changes per hour. To find what capacity fan isneeded use the formulaQ = CV ; Q = 30 X 60 X 60 X 14 ; Q = 75600

60 60 60Q= 1,260 c.f.m.(Sec. 28, Pars. 10 and 11)

5. To reduce air duct friction loss you would increase theduct size. (Sec. 29, Par. 3)

6. Duct fire dampers are used to automatically shut off fansand ducts in event of a fire. (Sec. 29, Par. 5)

7. The type of grille that should be used in a flood airoutlet which requires controlled airflow is a vaned grille.(Sec. 30, Pars. 2-7)

8. Slotted outlets are used for long narrow rooms. (Sec. 30,Par. 6)

9. The pattern of the supply air envelope is determined bythe air outlet grille. (Sec. 31, Par. 3)

10. Several of the factors that must be considered whenpreparing to install a ventilating system are: the purposeof the building or room to be ventilated, the temperatureand humidity of the region; the size of the building orroom, the number of occupants, and local and nationalcodes and regulations. (Sec. 32, Pars. 1-3)

11. In a room that contains carbon dioxide the fan shouldbe located close to the floor. The specific gravity ofcarbon dioxide is 1.527 which is heavier than air; so itwill settle to the floor. (Sec. 32, Pars. 18 and 19)

12. When installing an exhaust fan in a paint shop or paintspray booth, the electrical circuit for the fan and aircompressor should be interconnected. This will insurethat the fan is operating when spray painting is beingdone. (Sec. 32, Par. 22)

13. The factors that determine the desired exhaust airvelocity are: what is to be exhausted, amount to beexhausted, and the desired noise level. (Sec. 32, Pars.26-28)

14. Poorly constructed fixed wooden louvers would result inrestriction of airflow and insufficient protection againstbad weather. (Sec. 32, Par. 34)

15. Filters should be installed in the exhaust system whenthe discharge would create an objectionable condition inthe immediate area. (Sec. 32, Par. 39)

16. Dirt on the fan blades will unbalance the fan and causefan vibration during operation. (Sec. 33, Par. 5)

17. Overlubrication of fan motors and other ventilatingequipment will result in collections of oil and dirt whichcould restrict airflow, cause motors to overheat, andpresent a fire hazard. (Sec. 33, Par. 8)

18. The frequency of cleaning an air filter depends on thefollowing: type of system in which the filter is installed,how much the system is used, and weather conditions.(See. 33, Par. 16)

19. Excessively tight fan belts will cause an increase in thefan motor load and premature bearing wear. (Sec. 33,Par. 21)

CHAPTER 9

1. COP = 300,000 40 X 2545

= 300,000101,800

= 2.94 to 1(Sec. 34, Par. 2)

2. 100,000 B.t.u./hr. = 29.2 kw.-hr29.2 X .02 = $.584 per hour.584 X 24= $14.02 per day.(Sec. 34, Pars. 5 and 6)

3. You would have 5400 degree days.65 - 5 = 60 degree days per day.60 X 90 = 5400 degree days.(Sec. 34, Par. 7)

4. The heat pump is cheaper to operate because it useselectricity only to drive the compressor. Therefrigeration releases more heat per watt consumed.(Sec. 34, Par. 8)

5. The oil-fired heating system is cheaper than the air-to-airheat pump. (Sec. 34, Par. 9)

6. The air-to-air (refrigerant changeover) heat pump hastwo expansion devices. (Sec. 35, Par. 2)

7. The maximum temperature of the refrigerant when theoutside temperature is 50° F. is 75° F. (Sec. 36, Par. 2)

8. Outdoor temperature is an important factor because abalance point above the design temperature wouldrequire supplemental heating which is not economical.(Sec. 36, Pars. 3-9)

9. 40 pounds of frost on a 5-feet x 4-feet coil will notsubstantially affect the coil because the nominal amountit could hold is 50 pounds. (Sec. 36, Par. 11)

10. A 4-foot coil can contain 384 to 672 fins. (Sec. 36, Par.15)

11. The most common causes of airflow reduction are dirtyfilter, dirty coils, and frost accumulation on the coil.(Sec. 36, Par. 19)

12. City water is not considered a good heat source becauseof its poor availability and high operating cost. (Sec. 36,Par. 24)

13. Well water is considered the best heat source because ofits relatively constant temperature. (Sec. 36, Par. 25)

14. Heat storage is beneficial to a heat pump because ittends to reduce the rate of temperature change and helpsto reduce peak load requirements. (Sec. 37, Par. 2)

15. The solenoid pilot 3-way valve has probablymalfunctioned when the unit will not reverse its cycle.(Sec. 38, Par. 2)

16. When the pilot valve is energized, suction pressure isallowed to pass to the top of the main valve piston.This will cause the piston to rise, allowing thecompressor discharge to pas to the condenser. (Sec. 38,Par. 3)

17. An open in the pilot valve solenoid will cause the heatpump to operate on the heat cycle. (Sec. 38, Par. 4)

18. To prevent freeze-up of a water-cooled condenser duringthe heat cycle, you should install an evaporator pressureregulator or a constant pressure liquid expansion valveon the condenser. (Sec. 38, Pars. 9 and 10)

138

SUBCOURSE EDITION OD1750 A

REFRIGERATION AND AIRCONDITIONING IV

(EQUIPMENT COOLING)

REFRIGERATION AND AIR CONDITIONING IV(EQUIPMENT COOLING)

Subcourse OD1750Edition A

United States Army Combined Arms Support CommandFort Lee, VA 23801-1809

14 Credit Hours

INTRODUCTION

This subcourse is the last of four subcourses devoted to basic instruction in refrigeration and air conditioning.

The scope of this subcourse takes in unit components of the absorption system, including their functions andmaintenance; water treatment methods and their relationship to centrifugal systems; centrifugal water pumps and electroniccontrol systems, including the relationship of amplifier, bridge and discriminator circuits to electronic controls.

The subcourse consists of three lessons.

Lesson 1. Direct Expansion and Absorption System.

2. Centrifugal Systems and Water Treatment.

3. Centrifugal Water Pumps and Electronic Control Systems.

Unless otherwise stated, whenever the masculine gender is used, both men and women are included.

CONTENTSPage

Preface.................................................................................................................................................................... ii

Acknowledgment.................................................................................................................................................... iii

Lesson 1Chapter

1 Direct Expansion Systems ..................................................................................................................................... 1

2 Absorption Systems ............................................................................................................................................... 26

Lesson 2Chapter

3 Centrifugal Systems ............................................................................................................................................... 46

4 Water Treatment ................................................................................................................................................... 77

Lesson 3Chapter

5 Centrifugal Water Pumps)...................................................................................................................................... 96

6 Fundamentals of Electronic Controls..................................................................................................................... 103

7 Electronic Control Systems ................................................................................................................................... 132

Answers to Review Exercises................................................................................................................................. 139

The passing score for ACCP material is 70%.

Preface

YOU HAVE studied the fundamentals and commercial refrigeration and air-conditioning systems. This final volume dealswith another phase of your career ladder-equipment cooling. Since the principles of equipment cooling are common to allrefrigeration systems, your mastery of the subject should be easy. All of the systems covered in this volume can be appliedto commercial refrigeration and air conditioning.

To qualify you in equipment cooling, we will present the following systems in this volume:

(1) Direct expansion(2) Absorption(3) Centrifugal(4) Water treatment(5) Centrifugal water pumps(6) Fundamentals of electronic controls(7) Electronic control

Keep this memorandum for your own use.

ii

ACKNOWLEDGMENT

Acknowledgment is made to the following companies for the use of copyright material in this CDC: Honeywell,Incorporated, Minneapolis, Minnesota; Carrier Air Conditioning Company, Carrier Parkway, Syracuse, New York; TerrySteam Turbine Company, Hartford, Connecticut; Koppers Company, Incorporated, Baltimore, Maryland

iii

CHAPTER 1

Direct Expansion Systems

JUST WHAT DO we mean when we say "directexpansion"? In the dictionary we find that the word"direct" means an unbroken connection or a straightbearing of one upon or toward another; "expansion"relates to the act or process of expanding or growing (insize or volume). Now we can see that a direct expansionsystem for equipment cooling is one in which thecontrolled variable comes in direct contact with the singlerefrigerant source, thereby causing the liquid refrigerantto boil and expand. The centrifugal and absorptionsystems differ in that that they us a secondary refrigerant-water or brine-to cool the variable.

2. We will cover various components peculiar tolarge direct expansion systems, normally of 20 tons ormore in capacity. Remember, the window- and floor-mounted air-conditioning units are also considered directexpansion systems. Before we discuss the installation ofa semihermetic condensing unit-the most commonly usedunit for direct expansion systems-we will cover thevarious coils that are used in a direct expansion system.The application of the water-cooled semihermeticcondensing unit will concern us in the second section,and we will conclude the chapter with system servicingand troubleshooting.

1. Coil Operation1. There are three coils used in the typical system.

From the outside in, the coil sequence is: (1) preheat, (2)direct expansion (D/X), and (3) reheat. We will discussthe application of these coils, their use and control, andthe valves and dampers which control the flow of waterand air.

2. Preheat Coil. You must consider three thingsbefore installing a preheat coil in an equipment coolingsystem. These are:

(1) Is preheat necessary? (2) Will the coil be subjected to subfreezing

temperature?(3) What size preheat coils are needed?

3. After you have determined a need, provided forfreezing temperatures, and correctly sized the coil, you

are ready to install the coil. The next problem is whereto install it. The preheat coil is installed in the outside airduct, before the mixing of outside and return air. Nowwe are ready to discuss a few applications of a preheatcoil.

4. Thermostatically controlled water or steam valve.Figure 1 shows a system that uses a narrow rangetemperature controller. The temperature of the incomingair is sensed by the thermostat feeler bulb. Thethermostat is calibrated to modulate the valve open whenthe temperature is 35° F.

5. The damper on the face of the preheat coilcloses when the fan is turned off and opens when it isturned on. This damper is normally closed when the fanis off or if the fan fails to operate. This prevents preheatcoil freezeup.

6. Thermostatically controlled face and bypassdampers. The mixed air temperature remains relativelyconstant until the outside air temperature exceeds thedesired mixed air temperature. The use of the face andbypass damper, illustrated in figure 2, makes it possible tocontrol mixed air temperature without endangering thepreheat coil. The damper is controlled by a temperaturecontroller in the mixed air duct while the preheat coil iscontrolled by a valve which is modulated by a narrowrange temperature controller in the outside air duct. Theface and bypass damper will close and the return airopens when the supply fan is turned off.

7. D/X Coil. In equipment cooling systems, theD/X coil is located after the preheat coil. It serves twoprimary functions-cooling and dehumidification.

8. Simple on-off control. The compressor iscontrolled by a space thermostat in an on-off manner.Figure 3 shows a system using this type of control. Thissystem is best suited for use on small compressors andwhere large variations in temperature and humidity arenot objectionable.

1

Figure 1. Control of preheat with outdoor airthermostat.

9. The differential adjustment on the thermostatshould be set relatively wide to prevent short cyclingunder light load conditions. The control circuit isconnected to the load side of the fan starter so thatturning on the fan energizes the control systems.

10. Two-speed compressor. Figure 4 shows a typicaltwo-speed compressor installation. A two-stagethermostat (space) cycles the compressor between lowspeed and off during light load conditions and cycles theunit between high and low speed during heavier loads.The thermostat also shuts off the compressor if the spacetemperature falls below the set point.

11. The humidistat cycles the compressor from lowto high speed when space humidity rises above the highlimit set point. It can do this when the compressor is onlow speed. This system is best suited for use onreasonably small compressors where large swings intemperature and relative humidity can be tolerated.

12. Solenoid valve installation. Figure 5 shows asystem which uses a space thermostat to operate asolenoid valve and a nonrestarting relay. The

Figure 2. Preheat control with bypass and return air dampers.

Figure 3. On-off compressor control.

two-position thermostat opens the refrigerant solenoidvalve when the space temperature rises and closes itwhen the temperature drops below the set point. Thiscontrol action will cause large swings in temperature andrelative humidity. The nonrestarting relay prevents shortcycling of the compressor during the off cycle. It allowsthe compressor to pump down before it cycles "off."

13. Multiple D/X coil solenoid valves. The systemshown in figure 6 is similar to that previously discussed(fig. 5) except that it now has two D/X coils and twosolenoid valves. The two-stage space thermostat operatesD/X coil 1 in an on-off manner when the cooling load islight. It also holds the valve to coil 1 open and operatesthe valve to coil 2 in an on-off manner during heavy loadconditions. The nonrestarting relay functions the sameas the one in figure 5.

14. The supply fan starter circuit must be energized,in both applications, before the control circuit to thesolenoid valves can be completed.

15. Two-position control and modulating control of aface and bypass damper. This system uses a face andbypass damper (shown in fig. 7) to bypass air around theD/X coil during light load conditions. The spacethermostat opens the refrigerant solenoid valve when theface damper opens to a position representing a minimumcooling

Figure 4. Two-speed compressor control.

2

Figure 5. On-off control with a solenoid valve.

load. It also modulates the face and bypass dampers tomix the cooled air with the bypassed air as necessary tomaintain the correct space temperature. A capacitycontrolled compressor must be used if short cycling,under light load conditions, is to be avoided.

16. It is necessary to adjust the face damper so thatit does not close completely. This will help prevent coilfrosting under light load conditions. The control circuitto the solenoid valve is wired in series with the supplyfan motor. When the fan is shut off, the solenoid valvewill close.

17. Two-position control and modulating control of areturn air bypass damper. This system, shown in figure 8,is similar to the system we have just discussed. The onlydifference is that we bypass return air instead of mixedair under light load conditions.

18. Reheat Coil. The reheat coil is used to heat theair after it has passed through the D/X coil. It expandsthe air, thus lowering the relative humidity. A D/X coiland reheat coil are used to control humidity.

19. Simple two-position control. Figure 9 shows asystem which uses a space thermostat to control a reheatcoil and a D/X coil. It opens the solenoid valve to theheating coil when the

Figure 6. On-off control of multiple D/X coil solenoid valves.

Figure 7. Two-position control of a D/X coil solenoid valveand modulating control of a face and bypass damper.

space temperature falls below the set point temperature,and opens the D/X coil solenoid valve when thetemperature is above the set point. A two-positionhumidistat is provided to open the cooling coil solenoidvalve when the space relative humidity exceeds the setpoint of the controller. When a humid condition exists,the humidistat will override the thermostat. Thethermostat senses the reduced air temperature and opensthe reheat coil solenoid valve which will lower therelative humidity. The D/X coil solenoid valve will closewhen the supply fan is shut off.

20. Control of dehumidification with a face and bypassdamper. We discussed the use of face and bypassdampers when we discussed D/X coils. Now we willapply this damper system to humidity control, as shownin figure 10. A space humidity controller is used to openthe D/X coil valve when a predetermined minimumdehumidification load is reached. It also modulates theface and bypass damper to provide the mixture ofdehumidified and bypass air necessary to maintain spacerelative humidity.

21. The space thermostat modulates the reheat coilvalve as needed to maintain space temperature. If thespace humidity drops below the set

Figure 8. Two-position control of a D/X coil solenoid valveand modulating control of a return air bypass damper.

3

Figure 9. Dehumidification control in a two-position D/Xsystem.

point of the humidity controller, and the spacetemperature rises because the discharge air is too warm tocool the space, the thermostat will open the D/X coilvalve and modulate the face and bypass damper to lowerthe space temperature. The reheat coil must becontrolled by a modulated valve so that the thermostatcan position the valve within its range. This will preventlarge swings in temperature and relative humidity. Thissystem also provides a method of closing the D/X coilvalve when the supply fan is shut off.

22. Control of dehumidification with a return air bypasssystem. Figure 11 shows a system which uses a return airbypass damper to control airflow across the D/X coil fordehumidification. The space humidistat opens the D/Xcoil valve when a predetermined minimum cooling loadis reached and positions the bypass damper to maintainspace relative humidity.

23. The space thermostat acts in a way that issimilar to that of the thermostat in figure 10. Thecontrol circuit to the D/X coil valve is connected to thesupply fan so that the valve will close when the fan isshut off. This arrangement helps prevent coil frosting andreheat coil freezeup.

Figure 10. Dehumidification control in a D/X face and bypasssystem.

Figure 11. Dehumidification control in a D/X return airbypass system.

24. We have discussed the three coils that you willfind in a typical equipment cooling system. Now we willdiscuss a complete system which maintains temperature,relative humidity, and air changes.

25. Typical D/X Equipment Cooling System.Figure 12 shows a system which may be used tocondition air for electronic equipment operation.Thermostat T1 senses outdoor (incoming) air andmodulates the preheat coil valve to the full open positionwhen the temperature falls below the controller set point.A further drop in temperature will cause the thermostatT1 to modulate the outside and exhaust air dampers shutand the return air damper open.

26. The space thermostat (T2) operates the reheatcoil valve as necessary to maintain a predetermined spacetemperature. The space thermostat (T2) will modulatethe cooling coil valve when the space humidity is withinthe tolerance of the humidistat. The space humidistatopens the cooling coil valve when a minimum coolingload is sensed. It has prime control of this valve. Theoutside and exhaust air dampers are fitted with a stop sothat they will not completely close. This procedureallows for the correct amount of air changes per hour.

27. There are many other direct expansion systems.The blueprints for your installation will help you to betterunderstand the operation of your system. Most of thesystem components are similar to those previouslydiscussed.

2. Application of Water-Cooled Condensing Units1. Water-cooled semihermetic condensing units arerated in accordance with ARI Standards with waterentering the condenser at 75°F.2. Condensing units are available for differenttemperature ranges. We are interested in the "hightemperature" unit, as it is used for air conditioning

4

Figure 12. Typical D/X equipment cooling system.

or other applications requiring a +25°F. to +50°F suctiontemperature.

3. A medium temperature unit (-10° F. to +25° F.)should not be selected or equipment cooling applicationswhere the compressor would be subjected to high suctionpressure over extended shutdown periods. This wouldresult in motor overload and stopping when the coolingload is peak. To prevent this possibility, the proper unitmust be selected considering the highest suction pressurethe unit will be subjected to for more than a brief periodof time.

4. Compressor Protection. During shutdown,refrigerant may condense in the compressor crank-caseand be absorbed by the lubricating oil. The bestprotection against excessive accumulation of liquidrefrigerant is the automatic pump-down control. Thecompressor must start from a low-pressure switch(suction pressure) at all times. Figure 19 (in Section 3)shows a recommended control wiring diagram thatincorporates an automatic pump-down control. Whenthe pressure in the crankcase rises, the compressor willcycle on. It will run until the pressure drops to the low-pressure switch cutoff setting.

5. In systems where the refrigerant-oil ratio is 2:1or less, automatic pump-down control may be omitted. Itmay also be omitted on systems where the evaporator isalways 40° or more below the compressor ambienttemperature. However, the use of an automatic pump-down control is definitely preferable whenever possible.

6. Water Supply. Water-cooled condensing unitsshould have adequate water supply and disposal facilities.Selection of water-cooled units must be based on the

maximum water temperature and the quantity of waterwhich is available to the unit. Now that you haveselected the proper equipment, let's discuss theinstallation of equipment.

3. Installation1. Before you start installing the unit you must

consider space requirements, equipment ventilation,vibration, and the electrical requirements.

2. The dimensions for the condensing unit aregiven in the manufacturer's tables. You must allowadditional room for component removal, such as thecompressor or dehydrator. The suction and dischargecompressor service valves, along with the compressor oilsight glass, must be readily accessible to facilitatemaintenance and troubleshooting. The space must bewarmer than the refrigerated space to prevent refrigerantfrom condensing in the compressor crankcase duringextended shutdown periods. Water-cooled units must beadequately protected from freezeup. Some method ofdrainage must be provided if the unit is to be shut downduring the winter months.

3. Install the unit where the floor is strong enoughto support it. It is not necessary to install it on a specialfoundation, because most of the vibration is absorbed bythe compressor mounting springs. On critical installations(e.g., hospitals and communication centers) it may bedesirable to inclose the unit in an equipment room toprevent direct transmission of sound to occupied spaces.Place the unit where it will not be damaged by traffic orflooding. It may be necessary to cage or elevate the unit.

4. The next step in installing a unit is to

5

Figure 13. Three phase wiring diagram for a semihermetic condensing unit.

inspect the shipment for loss or damage. You mustreport any loss or damage to your supervisor immediately.Refer to ASA-B9.1-1953, American StandardsAssociation's "Mechanical Refrigeration Safety Code"when you install the unit.

5. Before installing the unit, check the electricservice to insure that it is adequate. The voltage at themotor terminals must not vary more than plus or minus10 percent of the rated nameplate voltage requirement.Phase unbalance for three-phase units must not exceed 2percent. Where an unbalance exists, you must connectthe two lines with the higher amperages through theswitch heater elements. Figure 13 shows a typical wiringdiagram for a semihermetic condensing unit.

6. A table of wire size requirements is providedwith the manufacturer's installation handbook. Forinstance a 220-volt three-phase condensing unit requiring8 amperes at full load must be wired with number 8 wire

if the length the run is 300 feet. However, number 14wire can be used if the run is limited to 10 feet.

7. Piping and Accessories. The liquid and suctionlines are usually constructed of soft copper tubing. Tohelp absorb vibrations, loop or sweep the two lines nearthe condensing unit. Use a vibration isolation typehanger, show in figure 14, to fasten the tubing on wallsor supports.

8. Shutoff valves. The suction and dischargeshutoff valves (service valves) are of the back-seating typeand have gauge ports. Frontseating the valve closes therefrigerant line and opens the gauge port to the pressurein the compressor.

9. Backseating the valve shuts off pressure to thegauge port. To attach a gauge or charging line to thegauge port, backseat the valve to prevent escape ofrefrigerant.

6

Figure 14. Vibration isolation type hanger.

10. Use a square ratchet or box-end wrench (1/4-inch) to open and close the valve. Do not use pliers oran adjustable wrench since they are likely to round thevalve stem. Do not use excessive force to turn the stem.If it turns hard, loosen the packing gland nut. If thevalve sticks on its seat, a sharp rap on the wrench willusually break it free.

11. Liquid line solenoid valve. Many manufacturersuse this type of valve on their units to prevent damage tothe compressor which would result from flooding of thecrankcase with refrigerant during shutdown. This type ofvalve also provides a compressor pump-down feature onmany units. The valve is installed in the liquidrefrigerant line directly ahead of the expansion valve. Itmust be installed in a vertical position and wired asshown in the wiring diagram (fig. 13).

12. Liquid line sight glass. The liquid line sight glassis installed between the dehydrator and expansion valve.You should locate the sight glass so that it is convenientto place a light behind the glass when you are observingthe liquid for a proper charge.

13. Water regulating valves. Install the waterregulating valve with the capillary down and the arrow onthe valve body in the direction of water-flow. Backseatthe liquid line shutoff valve and connect the capillary ofthe water regulating valve of the 1/4-inch flareconnection on the liquid line shutoff valve. Open theshutoff valve one turn from the backseated position.This allows refrigerant pressure to reach the waterregulating valve and still leaves the liquid line open.

14. Water-cooled condenser connections. When citywater is used as the condensing media, the condensercircuits are normally connected in series. When coolingtower water is used for condensing, the condenser circuitsare connected in parallel. See figure 15 for correctcondenser water connections.

15. Leak Testing the System. After all thecomponents have been installed, you are ready to leaktest the system. Charge the system with dry nitrogen orcarbon dioxide (40 p.s.i.g.) and check all the joints with asoap solution. Release the pressure and repair any leaksthat may have been found. After the leaks have beenrepaired, charge the system with the recommendedrefrigerant to 10 p.s.i.g. Add enough dry nitrogen orcarbon dioxide to build the pressure to 150 p.s.i.g. andleak test with a halide leak detector. Purge the systemand repair all leaky joints that you may have found. Donot allow the compressor to build up pressure sinceoverheating and damage may result. Do not use oxygento build up pressure!

16. Dehydrating the System. Moisture in thesystem causes oil sludge and corrosion. It is likely tofreeze up the expansion valve during operation. The bestmeans of dehydration is evacuation with a pumpespecially built for this purpose. The condensing unit isdehydrated at the factory and is given a partial or holdingcharge. Leave all the service valves on the condensingunit closed until the piping and accessories have beendehydrated. Do not install a strainer-dehydrator until thepiping is complete and the system is ready for evacuation.

Figure 15. Condenser connections.

7

Figure 16. Vacuum indicator.

17. Make the following preparations beforedehydrating the system:

(1) Obtain a vacuum pump that will produce avacuum of 2 inches Hg absolute. Do not use thecompressor as a vacuum pump since this may causeserious damage to the compressor.

(2) Obtain a vacuum indicator similar to that shownin figure 16. These indicators are available throughmanufacturers' service departments.

(3) Keep the ambient temperature above 60° F. tospeed the evaporation of moisture.

18. Description and use of the vacuum indicator. Thevacuum indicator consists of a wet bulb thermometer inan insulated glass tube containing distilled water. Part ofthe tube is exposed so that the thermometer can be readand the water level checked. When the indicator isconnected to the vacuum pump suction line, thethermometer reads the temperature of the water in thetube. The temperature is related to the absolute pressurein the tube. Figure 17 gives the absolute pressurescorresponding to various temperatures. To determine the

vacuum in inches of mercury, subtract the absolutepressure from the barometer reading.

19. Handle the vacuum indicator with care. It mustbe vacuum-tight to give a true reading. The top seal ofthe indicator is not designed to support a long run ofconnecting tubes. Fasten the tubes to supports to preventdamage to the indicator. Use only distilled water in theindicator and be sure the wick is clean. Oil or dirt on thewick causes erroneous readings.

20. To prevent loss of oil from the vacuum pumpand contamination of the indicator, you must installshutoff valves in the suction line at the vacuum pumpand the vacuum indicator. When shutting off the pump,close the indicator valve and pump valve, and then turnoff the pump. Now we are ready to dehydrate thesystem.

21. Procedure for dehydrating the system. Connect thepump and vacuum indicator to the system. Put a jumperline between the high and low side so that the pump willdraw a vacuum on all portions of the system. Open thecompressor shutoff valves and start the vacuum pump.Open the indicator shutoff valve occasionally and take areading. Keep the valve open for at least 3 minutes foreach reading. You must keep the indicator valve closedat all other times to decrease the amount of water thepump must handle and to hasten dehydration. When thepressure drops to a value corresponding to the vaporpressure of the water in the indicator, the temperaturewill start to drop.

22. In the example illustrated in figure 18, theambient temperature and the temperature of the water inthe indicator is 60° F. Starting at 60° F., and 0 time, thetemperature of the indicator water remains at 60° F. untilthe pressure in the system is pulled down to the pressurecorresponding to the saturation temperature of the water(60° F.). Point A in figure 18 shows the temperaturesaturation point. At this point the moisture in the systembegins to boil. The temperature drops slowly until thefree moisture is removed. Point A to Point B illustratesthe time required for free moisture evaporization. Afterthe free moisture is removed, the

Figure 17. Temperature-pressure relationship.

8

Figure 18. Dehydration pulldown curve.

absorbed moisture is removed, point B to point C.Dehydration is completed at point C, provided theambient temperature stays at 60° F. or higher. If theambient temperature falls below 60° F., the moisture willform ice before moisture removal is complete.

23. You should continue the dehydrating procedureuntil the vacuum indicator shows a reading of 35° F.Looking back at figure 17, you will find that a 35° F.reading corresponds to a pressure of 0.204 inch Hgabsolute. This procedure may take several hours, andmany times it is advantageous to run the vacuum pumpall night. After evacuation, turn off the indicator valve(if open) and the pump suction shutoff valve, and breakthe vacuum with the recommended refrigerant.Disconnect the pump and vacuum indicator.

24. Charging the System. The refrigerant may becharged into the low side of the system as a gas or intothe high side as a liquid. We will discuss both methodsof charging in this section.

25. To charge into the low side as a gas, backseatthe compressor suction and discharge valves and connectyour gauge and manifold to the appropriate compressorgauge connections The next step is to connect arefrigerant drum to the middle manifold hose. Open thedrum valve and purge the hoses, gauges, and manifold.Then tighten all the hose connection. Turn the suctionshutoff valves a couple of turns from the backseatposition and open the drum valve as far as possible.

Remember, keep the refrigerant drum in an uprightposition to prevent liquid refrigerant from entering thecompressor. You can now turn the compressor dischargeshutoff valve about one-fourth to one-half turn from thebackseat position so that compressor discharge pressurecan be read at the manifold discharge pressure gauge.

26. Before you start the compressor you mustcheck the following items:(1) Proper oil level in the compressor sight glass

(one-third to two-thirds full).(2) Main water supply valve (water-cooled

condenser).(3) Liquid line valve. Valve stem should be

positioned two turns from its backseat to allow pressureto be applied to the water regulating valve.

(4) Main power disconnect switch (ON position).27. After you have started the compressor you must

check the following items:(1) Correct oil pressure.(2) Water regulating valve adjustment.(3) Control settings.(4) Oil level in the compressor crankcase.28. Check the refrigerant charge frequently while

charging by observing the liquid line sight glass. Therefrigerant charge is sufficient when flashing (bubbles)disappears. If the pressure within the drum, duringcharging, drops to the level of the suction pressure, all theremaining refrigerant in the drum may be removed byfrontseating the compressor suction shutoff valve.

9

This procedure will cause a vacuum to be pulled on therefrigerant drum.

29. When the system is sufficiently charged, closethe refrigerant drum valve and backseat the compressorsuction and discharge shutoff valves. Disconnect thecharging lines from the compressor gauge ports andconnect the lines from the dual pressurestat to thecharging lines and "crack" the valves off their backseat.

30. Liquid charging into the high side can be doneby either of two methods. One method is to charge intothe liquid line with the compressor running. The othermethod is to charge directly into the systems liquidreceiver. Since charging liquid into the receiver is muchfaster, systems containing more than 100 pounds ofrefrigerant are usually charged this way. Let us discussboth methods in detail.

31. Systems to be charged into the liquid line firstmust have a charging port installed in the liquid line.Then use the following procedure:

(1) Close king valve.(2) Connect inverted drum to charging port.(3) Open drum service valve.(4) Purge air from charging lines.(5) Operate unit until fully charged.(6) Reopen king valve; this system is now in

operation.32. Charging liquid into the receiver is performed

according to the following general procedure:(1) Turn off electrical power to unit.(2) Connect the inverted and elevated refrigerant

drum to the receiver charging valve.(3) Open drum service valve.(4) Purge air from charging line.(5) Open the charging valve.(6) Several minutes are required to transfer a drum

of refrigerant in this manner; the transfer time can beshortened by heating the drum (do not use flame).

(7) When sufficient charge has been transferred intothe system, power can be turned on.

(8) By checking the pressure gauges and the sightglass, you can determine when the system is fullycharged. To maintain the efficiency of the machineryyou have installed, you must service and troubleshoot it.

33. Checking Operation. When you are starting anewly installed compressor, be on the alert for any signof trouble.

34. The high-pressure setting of the dualpressurestat, shown in figure 19, should not require achange; however, the low-pressure setting will probablyrequire adjustment, depending upon the evaporatortemperature. Check the high-pressure cutout by

throttling the condenser water. This will allow the headpressure to rise gradually. The cut-out and cut-inpressures should be within 10 to 15 pounds of the valuesoutlined in the manufacturer’s handbooks. If they arenot, the pressurestat would be readjusted. You can checkthe low-pressure settings by frontseating the compressorshutoff valve or the liquid line shutoff valve. The cut-inand cut-out point may be adjusted if it is necessary.

35. The units are shipped with "full" oil charges.Do not assume that the charge is sufficient. Stop theunit, without pump-down, after 15 or 20 minutes ofoperating time and immediately recheck the oil level inthe compressor sight glass. The oil level must be one-third to two-thirds of the way up on the sight glass. Youcan check oil pump pressure by looking at the oil pressurerelief valve through the sight glass during compressoroperation. Pressure is adequate if oil is being dischargedfrom the relief valve.

36. Adjust the water regulating valve to the mosteconomical head pressure for the locality. Normally, thisis 120 to 140 p.s.i.g. for R-12 and 200 to 230 for R-22.4. Servicing and Troubleshooting

1. We have covered several service techniques inthe previous section that relate to installation, includingleak testing, dehydrating, and charging into the low sideas a gas and into the high side with liquid. We shall nowgo further into servicing as it relates to disassembly,inspection, and reassembly of individual components. Bymeans of tables at the end of this chapter, you will thenfocus on troubleshooting techniques.

2. Servicing. Servicing direct expansion systemsembodies a wide range of related topics, from removingthe refrigerant charge and testing for leaking valves toterminal assembly and testing capacitors and relays.

3. Removing Refrigerant. The refrigerant chargecan be removed by connecting a refrigerant drum to thegauge port of the liquid line shutoff valve. Turn thestem two turns off its backseat and run the unit. Mostof the refrigerant can be removed in this manner. Theremainder may be removed by placing the drum in abucket of ice or by slowly releasing it to the atmosphere.

4. Pump-down procedure. If possible, you shouldallow the compressor to run until it is warm beforepumping it down. Then pump the system down asfollows:

(1) Close (frontseat) the liquid line shutoff valve onthe condenser.

(2) Hold the pressurestat switch closed so that theunit will not trip off on low pressure.

(3) Run the compressor until the compound

10

Figure 19. Single-phase wiring diagram for a semihermetic condensing unit.

gauge (registering low side pressure) registers 2 p.s.i.g.(4) Stop the compressor and watch the gauge. If

the pressure rises, pump down again. Repeat theoperation until the pressure remains at 2 p.s.i.g.

(5) Frontseat the compressor discharge and suctionshutoff valves.

(6) If the compressor is to be left pumped down forany period, tag the disconnect switch to preventaccidental starting of the unit.

5. If the compressor is the only component to beremoved, pumping down the crankcase will be sufficient.This may be done by front-seating the suction shutoffvalve and completing steps (1)-(5) listed under pump-down procedure.

11

You must stop the compressor several times duringpump-down to prevent excessive foaming of the oil asthe refrigerant boils out since the foaming oil may bepumped from the crankcase.

6. Breaking refrigerant connections. When itbecomes necessary to open a charged system, thecomponent or line to be removed or opened should bepumped down or evacuated to 2 p.s.i.g. You must allowenough time for all adjacent parts to warm to roomtemperature before you break the connection. Thisprevents moisture from condensing on the inside of thesystem.

7. After the component has warmed to roomtemperature, you are ready to break the connection andmake the necessary repairs.

8. Cleaning the expansion valve strainer. To cleanthe expansion valve strainer, you must close the liquidline shutoff valve and pump down the system to 2 p.s.i.g.Disconnect the valve and plug the tube ends. Removethe screen and clean it with a recommended cleaningsolvent. After the screen is clean and dry, reinstall it inthe valve and connect the valve in the system. Purge thelines and valves; then open (two turns off the backseat)the liquid line shutoff valve.

9. Cleaning suction strainers. Most suction strainersare located in the suction manifold on the compressor.Pump down the compressor to 2 p.s.i.g. and frontseat thedischarge shutoff valve. At this point, you must checkthe manufacturer’s handbook to locate the strainer.Remove and clean it with solvent. After the strainerdrys, replace it, purge the compressor, and start the unit.Figure 20 shows two different types of strainers, basketand disc, and their location in the compressor motor.

10. Purging noncondensable gases. Noncondensablegases (air) collect in the condenser (water-cooled) abovethe refrigerant. The presence of these gases causeexcessive power consumption, a rise in leaving watertemperature, and high compressor discharge pressure.

11. To purge these gases from the system, stop thecompressor for 15 to 20 minutes. Then open the purgecock (if available) or loosen a connection at the highestpoint of the condenser for a few seconds. After purgingis completed, close the purge cock (or tighten theconnection) and run the compressor. If the dischargepressure is still high, repeat the procedure until thedischarge pressure returns to normal.

12. Adding oil. Add only the recommended oillisted in the manufacturer's handbook. The oil should betaken directly from a sealed container. Do not use oilthat has been exposed to the atmosphere because it maycontain some absorbed moisture.

13. To add oil, pump down the compressor to 2p.s.i.g. Remove the oil filter plug (if available) ordisconnect the pressurestat connection on the suctionmanifold. Insert a funnel and pour in the oil. Hold theoil container close to the funnel to minimize contact withthe air. The correct amount of oil needed can beestimated by observing the oil sight glass (one-third totwo-thirds full). After sufficient oil is added, connect thepressurestat or replace the oil filler plug, purge thecompressor, and start the unit.

14. Removing oil. To remove excess oil from thecrankcase, pump down the compressor to 2 p.s.i.g.Loosen the oil plug (if available), allowing the pressure toescape slowly. Then use a hand suction pump to removethe desired amount of oil. If a filler plug is not available,loosen the bottom plate or drain plug. Retighten theplate or plug when the oil assumes a safe level in thecrankcase one-third to two-thirds full. Purge and startthe compressor.

15. Testing for leaking valves. Leaky compressorvalves will cause a serious reduction in the capacity of thesystem. Install a manifold and gauge set. Start thecompressor and allow it to run until it is warm; thenfrontseat the suction shutoff valve. Pump down thecompressor to 2 p.s.i.g. Stop the compressor and quicklyfrontseat the discharge shutoff valve. Observe thesuction and discharge gauges. If a discharge valve isleaking, the pressures will equalize rapidly. Themaximum allowable discharge pressure drop is 3 p.s.i.g.per minute.

16. There is no simple method of testing suctionvalves. If there is an indicated loss of capacity and thedischarge valves check properly, you must remove thehead and valve plate and check the valves physically.

17. Disassembly, inspection, and reassembly of valveplates. Pump down the compressor to 2 p.s.i.g. andremove the compressor head capscrews. Tap the headwith a wooden or plastic mallet to free it if it is stuck andremove the cylinder head.

18. Remove the discharge valves and valve stops asshown in figure 21. Free the valve plate from the dowelpins and cylinder deck. Many valve plates have tappedholes. The capscrews are screwed into them andfunction as jacking screws. Now you can remove thesuction valves from the dowel pin. Figure 22 shows thesuction valve and suction valve positioning spring.Inspect the valve seats and valves. If the valve seats lookworn or damaged, replace the valve plate assembly (fig.21).

19. It is preferable to install new valves with a newvalve plate. If new valves are not available, turn the oldvalves over and install them

12

Figure 20. Suction strainers

with the unworn seat toward the valve seat. If the valveseats and valves are not noticeably worn, it is still goodpractice to turn the discharge valves; otherwise they maynot seat properly.

20. The suction valves are doweled and may bereinstalled as they were originally. You must neverinterchange valves. Be careful when replacing the suctionvalves. The positioning springs must be placed on thedowels first. Place them with their ends toward thecylinder deck and the middle bowed upward.

21. Worn valves may be reconditioned by lappingthem, using a fine scouring powder and a piece of glass.

Mix refrigerant oil with the powder to form a liquidpaste. Then move the valve in a figure 8 motion overthe paste and glass. After the valve is reconditioned,clean and reinstall it.

22. Use new valve plate and cylinder head gasketwhen you install the valve plate and cylinder head.

23. Disassembly, inspection and assembly of the oilpump and bearing head. Remove the oil pump cover,shown in figure 23. This will free the oil feed guideretainer spring and the oil feed guide. Then remove theoil pump drive segment.

13

Figure 21. Valve plate assembly.

24. After you remove the bearing head you canremove the plunger snaprings which hold the plunger,plunger spring, and guide spring in the pump plungercylinder. Snapring or jeweler's needle-nose pliers arerecommended for removing the shapings.

25. Push the pump rotor out of the bearing head bypressing against the bearing side of the rotor. The rotorretaining ring will come out with the rotor. Installing anew pump and bearing head is the only positive way ofeliminating oil pump trouble. However, if the cause ofthe trouble is determined, replacement parts are availablefor almost all compressors.

26. The first step in installing the oil pump andbearing head is to install the rotor retaining ring in thering groove of the rotor, with the chamfered edge towardthe compressor. Compress the retaining spring and insertthe pump rotor into the bearing head.

27. The plungers (flat ends in), plunger springs,spring guides, and snaprings are installed in the plungercylinders. Compress the snaprings and force them intotheir grooves. Place a new bearing head gasket and thebearing head into position and bolt them to thecrankcase. Install the drive segment. Be careful not toforget the lockwashers (shown in fig. 23). Insert the oilfeed guide with the large diameter inward. Place theguide spring so that it fits over the

Figure 22. Suction valve positioning spring.

14

Figure 23. Compressor breakdown.

small diameter of the oil feed guide; then install a newpump cover gasket and pump cover.

28. Disassembly, inspection, and assembly of theeccentric shaft and pistons. Remove the oil pump andbearing head previously described. Remove the motorend cover, being careful not to damage the motorwindings. Do not allow the cover to drop off. You mustsupport it and lift it off horizontally until it clears themotor windings. Remove the bottom plate and block theeccentric so that it will not turn. Remove the equalizertube and lock screw assembly from the motor end of the

shaft. Look at figure 23 for the location of thesecomponents.

29. Pull the rotor out, using a hook through theholes on the rotor. Do not hammer on the motor end ofthe shaft or rotor since this may cause the eccentricstraps or connecting rods to bend.

30. Remove the bolts holding the counterweightsand eccentric strap shields onto the eccentric shaft.(Refer to fig. 24 during these procedures.) Remove theeccentric strap side shields and the pump endcounterweight through the

15

Figure 24. Removing counterweights and eccentric strap shields.

bearing head opening. The motor end counterweight willhang on the eccentric shaft until the shaft is removed.Pull the eccentric shaft through the bearing head opening.Rotate the shaft, tapping it lightly to prevent the eccentricstraps from jamming. Guide the straps off the shaft byhand. The eccentric straps and pistons are removedthrough the bottom plate opening.

31. The piston pin is locked in place with a lockring.The pin can be removed by tapping lightly on the

chamfered end of the pin (the end not having alockring).

32. Examine the parts to see that they are not wornbeyond the limits given in the manufacturer's handbook.To reassemble, follow the disassembly instructions inreverse order.

33. Terminal assembly. Refer to figure 25 for therelative positions of the parts. The washers

16

Figure 25. Terminal block breakdown.

are usually color coded and slightly different in size.Assemble them as shown.

34. The terminal mounting plate assembly isoriginally installed with a small space left between theouter terminal block and the surface of the mountingplate. This provides further tightening of the terminalbushing in case of a leak. To stop a leak, tighten theterminal block capscrews only enough to stop the leakage

of gas. Do not tighten the capscrews so that the terminalblock is flush with the mounting plate. If furthertightening will cause this situation, the terminal assemblymust be replaced.

35. To replace the assembly, pump down thecompressor to 2 p.s.i.g. and remove the assembly. Installthe new assembly, using the recommended

17

torque on the capscrews (1.5 ft. lbs.); purge and start thecompressor. Avoid excess torque since terminal blockand components are generally constructed of plastic orbakelite.

36. Testing capacitors and relay. The startingcapacitor used in single-phase units is wired as shown infigure 19. Capacitors are connected in series with onepower lead to the motor starting winding. Thesecapacitors may fail because of a short or open circuit. Ifthey are short circuited, the starting current draw will beexcessive. The compressor may not start and will causefuses to blow because of the increased load. If it isconnected in a circuit feeding lights, the lights will dim.A humming sound from the compressor motor indicatesimproper phasing between the starting and runningwindings caused by an open-circuited capacitor. To checkstarting capacitors, replace them with good capacitors andobserve the operation of the unit.

37. The running capacitors are connected across therunning and starting terminals of the compressor. Ifshort circuited, they will allow an excessive current topass to the start winding continuously. The compressormay not start. If it does, it will be cut off by the motorover-load switch. If they are open, the compressor willoperate, but will draw more power than normal whenrunning and will stall on heavy loads. To test for open-circuited capacitors, an ammeter should be connected inseries with one power lead. With good runningcapacitors, the current requirement will be less than it iswhen the capacitor is disconnected. An open capacitorwill cause no change in current draw when it isdisconnected.

38. The relay is the potential or voltage type. Thecontacts are normally closed when there is no power tothe unit and open approximately one-fifth of a secondafter power is applied. The operation of the relaymagnetic coil is governed by the voltage through itswindings. Upon starting, the counter EMF of the motorbuilds up, causing a rise in voltage through the relay coil.As the voltage across the coil rises, the magneticattraction of the relay arm overcomes the spring tension.This causes the arm to move and force the relay contactsopen. The starting capacitors, which are in series withthe starting winding when the relay contacts are closed,are disconnected from the circuit.

39. If the relay fails with the contacts open, thestarting capacitors will not be energized. The compressormotor will hum but will not start. After the power hasbeen on for 5 to 20 seconds, the overload relay will cutoff the power to the compressor motor.

40. To check the relay for contacts that fail to close,put a jumper across the relay contacts and turn on the

power. If the unit starts with the jumper, but will notstart without it, you must replace the relay.

41. When the relay fails with the contacts closed,the starting capacitors will continue to be energized afterthe compressor has come up to speed. The compressorwill start but will run with a loud grinding hum. Theoverload relay will shut the compressor off after thecompressor has run for a short time due to the extra loadof the start winding. This type of relay failure can causedamage to the motor windings and the running capacitor.

42. A visual inspection will determine if relaycontacts fail to open. Remove the relay cover andobserve its operation. If it does not open after the powerhas been applied for a few moments, you must replacethe relay.

43. Oil safety switch. Many units have oil safetyswitches which protect the compressor from low or no oilpressure. This control has two circuits-heater andcontrol.

44. This switch measures the difference between oilpump discharge pressure and crankcase pressure. If thenet oil pressure drops below the permissible limits, thedifferential pressure switch energizes the heater circuitwhich will cause the bimetal switch in the control circuitto open in approximately 1 minute. Low oil pressuremay result from the loss of oil, oil pump failure, wornbearings, or excessive refrigerant in the oil. Figure 26shows a typical oil pressure safety switch.

45. The differential pressure switch is factorycalibrated to open when the oil pump discharge pressureis 18 p.s.i.g. greater than the crankcase pressure. It willclose when the difference is 11 p.s.i.g. Its adjustmentshould not be attempted

Figure 26. Oil pressure safety switch.

18

in the field. If the differential pressure switch functionsproperly and the compressor continues to run after 1minute, the time-delay heater circuit is defective and theoil pressure safety switch should be replaced. The switchshould be checked monthly for correct operation.

46. Troubleshooting. One of your most importantresponsibilities is the troubleshooting and correction of

malfunctions of these systems. Throughout this chapterwe have given basic principles of D/X systems. Usingthis knowledge and the information that we haveprovided in tables 1 through 10, you should have littletrouble in achieving the desired skill levels.

TABLE 1

TABLE 2

TABLE 3

19

TABLE 4

TABLE 5

TABLE 6

TABLE 7

20

TABLE 8

TABLE 9

TABLE 10

Review Exercises

The following exercises are study aids. Write youranswers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the text. Do not submit your answers for grading.

1. There are three things which must be consideredbefore installing a preheat coil. Name them.(Sec. 1, Par. 2)

2. After you have inspected a thermostaticallycontrolled steam preheat coil, you find that the

valve is closed and the outside temperature is33° F. What is the most probable malfunction, ifany? (Sec. 1, Par. 4)

3. What two functions does a D/X coil serve?(Sec. 1, Par. 7)

4. What has occurred when a compressor usingsimple on-off control short cycles? (Sec. 1, Par.9)

21

5. What function does the humidistat serve on atwo-speed compressor installation? (Sec. 1, Par.11)

6. Why is a nonrestarting relay installed in asolenoid (D/X coil) valve installation? (Sec. 1,Par. 12)

7. A service call is received from Building 1020with a complaint of no air conditioning. Thesystem uses two D/X coils and two solenoidvalves. Which component should you checkbefore troubleshooting the solenoid valve controlcircuit? (Sec. 1, Par. 14)

8. What type compressor must be used when two-position control of a D/X coil and modulatingcontrol of a face and bypass damper areemployed to control air temperature? (Sec. 1,Par. 15)

9. The most probable cause of low supply airtemperature and high humidity in an equipmentcooling system ____________. (Sec. 1, Par.18)

10. How are large swings in relative humidityprevented when face and bypass dampers areused to control dehumidification? (Sec. 1, Par.20)

11. Which control has prime control of the D/Xcoil if a space thermostat and humidistat areinstalled in the system? (Sec. 1, Par. 26)

12. Answering a service call, what conclusion wouldyou make from these symptoms?(1) The suction pressure is high.

(2) The cooling load is at its peak.

(3) The motor is short cycling on its over loadprotector. (Sec. 2, Par. 3)

13. What would occur if you installed a mediumtemperature unit for a 40° F suction temperatureapplication? (Sec. 2, Par. 3)

14. What could cause the compressor on an airconditioner to start when the thermostatcontrolling the liquid solenoid valve is satisfied?Why? (Sec. 2, Par. 4, and fig. 19)

15. When may the automatic pump-down feature beomitted? (Sec. 2, Par. 5)

16. Name the four factors you should considerbefore you install a D/X system. (Sec. 3, Par. 1)

17. How can you correct the following situation?Refrigerant is condensing in the compressorcrankcase. (Sec. 3, Par. 2)

18. Is it necessary to install a condensing unit on aspecial foundation? Why? (Sec. 3, Par. 3)

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19. What is the minimum and maximum voltagesthat can be supplied to a 220-volt unit? (Sec. 3,Par. 5)

20. How much phase unbalance is tolerable betweenphases of a three-phase installation? (Sec. 3,Par. 5)

21. During gauge installation, in which position isthe shutoff valve set and why? (Sec. 3, Par. 9)

22. Where would you install a liquid line sight glassin the system? (Sec. 3, Par. 12)

23. When city water is used as the condensingmedium, the condenser circuits are connected in______________. (Sec. 3, Par. 14)

24. When cooling tower water is used, thecondenser circuits are connected in_________________. (Sec. 3, Par. 14)

25. Which types of gases may be used to pressurizethe system for leak testing? (Sec. 3, Par. 15)

26. After you have disassembled a compressor, youfind an excessive amount of sludge in thecrankcase. What caused this sludge? (Sec 3,Par. 16)

27. Why is it important to keep the ambienttemperature above 60° F. when you aredehydrating a system with a vacuum pump?(Sec. 3, Par. 17)

28. What pressure corresponds to a vacuumindicator reading of 45° F.? (Sec. 3, Par. 18, andfig. 17)

29. Why are shutoff valves installed in the vacuumpump suction line? (Sec. 3, Par. 20)

30. The type of moisture that is first removed froma refrigeration system is _____________moisture. (Sec. 3, Par. 22)

31. Why do you have to backseat the suction anddischarge shutoff valves before you connect thegauge manifold? (Sec. 3, Par. 25)

32. What four items must be checked before youstart a newly installed compressor? (Sec. 3, Par.26)

33. How does frontseating the suction shutoff valveaffect the low-pressure control? (Sec. 3, Par. 34)

34. Why do you place the refrigerant cylinder in icewhen you want to evacuate all the refrigerantfrom a system? (Sec. 4, Par. 3)

35. Why is a partial pressure, 2 p.s.i.g., allowed toremain in the system after pumpdown? (Sec. 4,Par. 4)

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36. Why should you allow sufficient time for acomponent to warm to room temperature beforeremoving it from the system? (Sec. 4, Par. 6)

37. The two types of suction strainers are_______________ and________________ (Sec. 4, Par. 9)

38. Where do noncondensable gases collect in awater-cooled refrigerating system? (Sec. 4, Par.10)

39. What condition most probably exists when thefollowing symptoms are indicated?(1) Excessive amperage draw.

(2) The condenser water temperature is normal.

(3) The discharge temperature, felt by hand atthe compressor discharge line, is abovenormal. (Sec. 4, Par. 10)

40. What would a discharge pressure drop of 10p.s.i.g. per minute with the discharge shutoffvalve frontseated indicate? (Sec. 4, Par. 15)

41. How are valve plates removed from cylinderdecks? (Sec. 4, Par. 18)

42. What is the emergency procedure that you canuse to recondition worn compressor valves?(Sec. 4, Par. 21)

43. How is the oil feed guide installed? (Sec. 4, Par.27)

44. Why should you use a hook device rather than ahammer to remove the rotor? (Sec. 4, Par. 29)

45. (Agree)(Disagree) The terminal block istightened flush with the mounting plate. (Sec.4, Par. 34)

46. The amount of torque required when tighteningthe capscrews on a terminal block is_______________. (Sec. 4, Par. 35)

47. The following complaint concerning aninoperative air conditioner is submitted to theshop: the air conditioner keeps blowing fuseswhen it tries to start. After troubleshooting theunit you find that the starting current draw isabove normal. Which component should youcheck and what should you check it for (Sec. 4,Par. 36)

48. What will cause a humming sound from thecompressor motor? (Sec. 4, Par. 36)

49. The contacts of the starting relay are normally_________________. (Sec. 4, Par. 38)

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50. What causes the contacts of the starting relay toopen? (Sec. 4, Par. 38)

51. Which type of relay failure can cause damage tothe motor windings? (Sec. 4, Par. 41)

52. The two circuits that make up the oil safetyswitch are _______________ and______________. (Sec. 4, Par. 43)

53. The pressure which cause the oil safety switch tooperate are ________________ and________________ (Sec. 4, Par. 44)

54. (Agree)(Disagree) The differential pressureswitch in the oil safety switch will open whenthe pressure differential drops. (Sec. 4, Par. 45)

55. What can cause an inoperative motor starter?(Sec. 4, table 1)

56. What should you suspect when the dehydrator isfrosted and the suction pressure is belownormal? (Sec. 4, table 2)

57. A loose feeler bulb for a thermostatic expansionvalve will cause an abnormally cold suction line.Why is the line cold? (Sec. 4, table 5)

58. A hissing expansion valve indicates_____________________. (Sec. 4, table 6)

59. Too much superheat will cause____________________. (Sec. 4, table 6)

60. During a routine inspection, you find the water-cooled condenser exceptionally hot. What arethe most probable faults and how should youcorrect them? (Sec. 4, table 7)

61. A low suction pressure and loss of systemcapacity indicates __________________.(Sec. 4, table 10)

62. How would you correct this fault: A capacitycontrolled compressor short cycling? (Sec. 4,table 10)

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CHAPTER 2

Absorption Systems

HOW ABSURD IT is to use water as a refrigerant;yet absorption systems do. You know that this can bedone only under specific conditions. Within a deepvacuum, water will boil (vaporize) at a very lowtemperature. For example, when a vacuum of 29.99inches is obtained, the water will boil at approximately40° Fahrenheit. Hence, vacuum is the key to absorptionair conditioning.

2. The absorption system is one of the simplest ofall types of automatic air-conditioning systems. Thoughthis machine has few moving parts, it has an immensecooling capacity. We shall discuss in this chapterterminology, identification, and function of unitcomponents; starting and operating procedures; andmaintenance of the absorption system.

5. Terminology, Identification, and Function of Units1. The complete absorption refrigeration unit

contains a generator, a condenser, an absorber, and anevaporator. The condenser and generator are combinedin the upper shell of the machine, while the evaporatorand absorber are combined in the lower shell, as shownin figure 27.

2. The heat exchanger, purge unit, solution pump,and evaporating pump are mounted between the supportlegs of the unit. The purge unit is used to removenoncondensables from the machine. The capacitycontrol valve controls the water leaving the condenser.This valve is controlled thermostatically by a remote bulbplaced in the chilled water line.

3. Figure 28 is a simple block diagram of theabsorption refrigeration cycle. The refrigerant used iscommon tap water and the absorbent is a special salt,lithium bromide.

4. To understand the operation of the refrigerationcycle, consider two self-contained vessels: one containingthe salt solution (absorber) and the other (evaporator)containing water, joined together as shown in item 1 offigure 28. Ordinary table salt absorbs water vapor whenit is exposed to damp weather. The salt solution in theabsorber has a much greater ability to absorb the watervapor from the evaporator. The water in the evaporatorboiling at a low temperature does the same job asrefrigerants R-12, R-13, and R-22. As the watervaporizes, the water vapor travels from the evaporator tothe absorber, where it is absorbed into the salt solution.The evaporator pump, shown in item 2 of figure 28,circulates water from the evaporator tank to a sprayheader to wet the surface of the coil. The cooling effectof the spray boiling at approximately 40° F. on the coilsurface chills the water inside the coil, and this chilledwater is

Figure 27. Absorption unit components.

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Figure 28. Absorption refrigeration cycle.

circulated in a closed cycle to the cooling coils. Thisrefrigeration effect is known as flash cooling.

5. In reference to item 3 of figure 28, note theaddition of the generator and accessory equipment.These components are necessary for continuous andefficient operation. The salt solution would becomediluted and the action stopped if it were not for theregeneration of the salt solution. To keep the saltsolution in the absorber at its proper strength so that itwill have the ability to absorb water, the salt solution ispumped to a generator where heat is used to raise itstemperature and boil off the excess water. The saltconcentrate is then returned to the absorber to continueits cycle. The water that is boiled off from the saltsolution in the generator is condensed in the condenserand returned to the evaporator as shown in item 4 of

figure 28. The heat exchanger uses a hot solution fromthe generator to preheat the diluted solution. This raisesthe overall efficiency because less heat will be required tobring the diluted solution to a boil. Condensing water,which is circulated through the coils of the absorber andthe condenser, removes waste heat from the unit. Bycomparing figure 29 with figure 27, you will get a betterunderstanding of the relation between basic operatingprinciples and an actual installation.

6. Controls. Figure 30 illustrates a typical controlpanel for an absorption refrigeration unit. The purposeof each control listed in this figure is described in thefollowing paragraphs. Turning the off-run-start switch (1)the START position energizes the electric pneumaticswitch (2), which activates the control system of theabsorption machine. Supply air pressure of 15 p.s.i.g. (3)passes to the chilled water thermostat (4), then to theconcentration limit thermostat (5), and finally to thecapacity control valve (7).

7. The chilled water thermostat (4) is a directacting control with a 7° F. differential. For every degreechange in the chilled water temperature, there isapproximately a 2-pound change in its branch line airpressure. Its thermal element is located in the leavingchilled water line. As the leaving chilled watertemperature drops below the control setting of thethermostat, the supply air pressure (3) is throttled, causingthe capacity control valve (7) to throttle the condenserwater quantity. With a constant load on the machine,the capacity control valve throttles just enoughcondensing water to balance the load.

8. The concentration limit thermostat (5) is a directacting bleed type control, with the thermal elementlocated in the vapor condensate well. Its purpose is toprevent the solution from concentrating beyond the pointwhere solidification results. At startup, the capacitycontrol valve (7) is closed and remains closed until thevapor condensate well temperature rises above the controlpoint of the concentration limit thermostat. As it does,the thermostat begins to throttle the air bleeding to theatmosphere, thus raising the branch line pressure (6) andopening the capacity control valve. This control valve onsome absorption models may be controlled electricallyinstead of pneumatically.

9. Safety controls. Two safety controls are usuallyused in the control systems. They are the chilled watersafety thermostat and the solution pressurestat. In moistinstances, any malfunction occurring during operation isimmediately reflected by a rise in the chilled watertemperature. The thermal element of the chilled watersafety

27

Figure 29. Absorption refrigeration cycle.

thermostat is located in the chilled water line leaving themachine. The control point is set approximately 10° F.above the design leaving chilled water temperature. Atemperature rise above the control point shuts off the airsupply. All control lines are then bled and the system is

shut down. When the off-run-start switch is in theSTART position, this control is bypassed. The switchshould not be placed in the RUN position until after youobtain a chilled water temperature below the controlsetting.

10. The solution pressurestat located in the

28

Figure 30. Control panel.

discharge line of the solution pump is set to cut in on arising pressure at 40 p.s.i.g. and cut out on a fallingpressure at 30 p.s.i.g. If for any reason the dischargepressure falls below the control point, the system will beshut down in the same manner as described above.

11. Special control. Special chilled water controllersmay be installed in the field for special applications.These controls are used to maintain the chilled watertemperatures within a plus or minus 2° F. Explosion-proof controls and motor are installed for specialapplications. Refer to the manufacturer's manual on theoperation and maintenance of these controls and motors.

12. Thermometers. Thermometers are installed inseveral locations in the system. Below is a general listingof thermometer locations and their purposes:

(1) Chilled water piping to indicate the enteringchilled water temperature.

(2) Chilled water pump suction piping to indicateleaving chilled water temperature.

(3) Condensing water piping entering the absorbersection.

(4) Condensing water piping leaving the absorbersection. For proper temperature measurements, thethermometer is located in the generator bypass line.

(5) Condensing water piping leaving the condensersection.

(6) Condensing water piping to indicate the totalcondensing water temperature to the cooling tower ordrain.

13. Pressure Gauges. Pressure gauges are installedin several locations in the system. The following is ageneral listing of gauge locations:

(1) Purge water line after the strainer and before thepurge water jet.

(2) Purge water line after the jet.(3) Steam line before the generator section.(4) Discharge line from the chilled water pump.

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(5) Discharge line from the condenser water pump.14. Water Seals. Older models of absorption

machines require mechanical seals on the solution andevaporator pumps. However, the newer machines havehermetically sealed pumps that eliminate the need formechanical seals. The older models require externalwater seals; therefore, it is necessary to supply a waterseal tank to maintain water on the seals for lubricationpurposes and so that water rather than air leaks into themachine in case the seals break or leak.

15. The water seal tank has a float control to limitthe quantity of water to the seals when the machine is inoperation. The operator must open the manual valvesupplying the seal water tank before startup and mustclose the manual valve on shutdown. This is thestandard method of control. The alternate method is onewhere a check valve is installed in the supply line to thetank, as well as an antisyphon vacuum breaker. Whenthe machine is shut down a visual check can be made todetermine the condition of the seal and to prevent a largequantity of water from leaking into the machine if theseal is worn or cracked. If mechanical seals have to bereplaced, the manufacturer's instructions must becarefully followed in order to do the job correctly andprevent the new seals from leaking. During operation,the evaporator pump makes up for the water lost by aseal; but during shutdown, it is possible to lose a largeamount of water from the tank if a large leak exists.Therefore, leaky seals must be replaced immediately.Having learned the importance of water seals in theabsorption system, we can now discuss the startingprocedures.

6. Starting Procedures1. Some absorption systems are completely

automatic and can be started by simply pushing a startbutton, while in other systems the machine is automaticbut the auxiliary equipment is manually operated. Thetype of startup determines the starting procedure.Therefore, each starting procedure is outlined separately,and the machine operator can perform the startingoperations applicable to the type of startup required.Even though some systems are automatic, it would beadvisable to check the system as described below beforestarting the unit.

2. Daily Startup. Use the following steps inperforming a normal startup.

(1) Check vacuum in machine (see Maintenance,Section 8).

(2) Check mechanical seals for leakage (seeMaintenance, Section 8).

(3) Check water level in evaporator sight glass.(4) Check absorber section for presence of water.(5) Start condensing water pump.(6) Check temperature of condensing water going to

machine. Do not start cooling tower fan until thecondenser water it has warmed up to the recommendedsetting.

(7) Start the purge unit.• Push start button on the purge control panel.• Open purge steam supply valve.• Check the standpipe for water seal circulation

before starting the pumps.(8) Start the chilled water pump and open the valves

to insure circulation through the evaporator tubes and air-conditioning equipment.

(9) Start the refrigerant pump and open the valve inthe refrigerant pump discharge line.

(10) Start the purging machine. Open the absorberpurge valve located in the purge line to the absorber.The generator purge valve located in the purge linebetween the absorber and generator must be open.

(11) Wait until the machine is completely purged.There will be a substantial drop in the leaving chilledwater temperature when the machine is completelypurged. If the leaving chilled water temperature does notdrop and there are no leaks in the machine, then thesteam jets should be cleaned.

(12) Open the main steam valve to the machine.(13) Check steam pressure supply to see that it is

within the proper range.(14) Place the control panel switch in the START

position.(15) Check the main air supply pressure gauge to

insure that 15 p.s.i.g. is supplied to the control panel.(16) Start solution pump. Be sure the strong solution

return valve is open at all times.(17) When the leaving chilled water temperature has

dropped below the safety thermostat setting, move thecontrol panel switch from START to RUN.

3. Startup After Standby Shutdown. Thisprocedure is basically the same as for daily startup. Thereare, however, additional preparation steps that must firstbe performed in order to put the machine in operationalcondition for startup. In order to prepare the machinefor startup, the nitrogen with which the machine hasbeen charged must be removed and a vacuum pulled onthe machine. This is done by operating the purge unituntil the machine has been purged of nitrogen and asatisfactory vacuum reading attained.

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4. Startup After Extended Shutdown: Thisprocedure is basically the same as for daily startup exceptfor the additional preparation steps that must first beperformed to put the machine in operational conditionfor startup. The preparations necessary after extendedshutdown are similar to an initial startup of a newmachine. The complete system must be prepared foroperation in these steps:

(1) Check all drains that should be closed in thechilled water and condensing water circuits.

(2) Fill the condensing water circuit.(3) Start the purge unit to remove all air and

nitrogen from the machine.(4) Fill the primary and secondary chilled water

circuits.(5) Purge the chilled water circuit of air.• Start the chilled water pump.• Open the diaphragm valve in the chilled water

pump discharge line.• Open the diaphragm valve in the chilled water

return line to the machine and continue purging until therecommended vacuum is obtained.

(6) Purge the refrigerant circuit. Do not start therefrigerant pump until chilled water is circulating throughthe evaporator tubes.

• Start the refrigerant pump.• Open the valve in the refrigerant pump discharge

line and allow the refrigerant to circulate until therecommended vacuum is obtained on the machine.

(7) Shut down the purge unit.(8) Shut down the primary chilled water circuit.• Close the diaphragm valve in the primary chilled

water pump discharge line.• Shut off the primary chilled water pump. The

machine is now in operational order and ready for instantstartup. The procedures for daily startup should now befollowed to place the machine in operation.7. Operating Procedures

1. You must make periodic checks on the machinewhile it is in operation and keep a daily operating log.Compare observations with the following recommendedoperating conditions and make any necessaryadjustments.

2. Evaporator, Absorber, and Generator Levels.As an operator you will have to visually check the sightglasses on the evaporator, absorber, and generator.

3. Evaporator sight glass water level. The normaloperating evaporator tank water level is approximately 1inch above the horizontal centerline. At a high level, thechilled water may spill over the evaporator tank into the

solution in the absorber, causing a loss of operatingefficiency. A low level will cause the chilled water pumpto cavitate (surge).

4. Solution level in absorber. Normal operating levelis approximately one-third of the absorber sight glass atfull load operation. At partial load operation, the solutionlevel will vary between one-third and two-thirds of thesight glass. The solution level may require adjustmentwhen the leaving chilled water temperature is changed,which is done by manually adjusting the chilled waterthermostat. If the setting is lowered, the solution levelwill drop and solution must be added. If the setting israised, the solution level will rise and solution must beremoved from the machine. Operating instructions forthe specific machine should be followed in adjusting thesolution level.

5. Solution boiling level in generator. The solutionboiling level is set at initial startup of the machine andshould not vary during operation. The boiling level canbe checked by looking into the mirror near the generatorbull's-eye. A light should be visible at all times. If thelight is obscured, the boiling level is too high and shouldbe adjusted. A temporary measure is to adjust thesolution flow by throttling the generator flow valve in theline to the generator. For more detailed procedures,consult the service bulletin for your machine on how tocheck high boiling.

6. Purging. Proper purging is necessary to obtainand maintain a vacuum on an absorption system.

7. Purge operation. Water pressure, steam pressure,and water temperature must be within recommendedlimits to insure satisfactory operation. The steamsupplied to the jets must be dry. Operate the jets withthe bleed petcock open at all times. When jets areoperating properly, the first stage will run hot, the secondstage warm or cool. When air is being handled, thesecond stage will tend to get hot. Wet steam will causethe first stage diffuser to run cold. If too wet, the purgesystem will not operate. Check the circulation of sealwater through the seal chambers. If water is circulatingthrough the seal chambers, there will be an overflow ofwater from the standpipe. If the purge unit stops becauseof salinity indicator operation, you must immediatelyclose the machine purge valve. Shut off the steam supplyto the steam jets and open the reset switch to shut offthe alarm. If lithium bromide should pass into the purgewater tank, the water should be drained and the tankflushed; also flush the steam jets and condenser. Cleanwater can be introduced in the pressure tap between thepurge valve and the first stage of the purge unit. Resumenormal operation by filling

31

Figure 31. Jet purge unit.

the tank, bleeding the pump, and closing the reset switch.8. Jet purge. On some systems, the jet purge,

shown in figure 31, has been adapted to the unit. It isentirely automatic and provides a source of very lowpressure which is capable of removing noncondensablesfrom the machine when required. Sincenoncondensables travel from high-pressure regions tolow-pressure regions-generator, condenser, evaporator,absorber--the purge suction tube is located in the lower

section of the absorber. The jet purge system is made upof the following components:

(1) Purge tank (12-gallon capacity).(2) Purge pump (submersible).(3) Jet evacuator (operates on the venturi principle).(4) Purge valve (usually operated by a hydromotor).(5) Adjustable drip tube (keeps solution in purge

tank at 53 percent).

32

(6) Purge cooling coil (keeps purge solution at a lowtemperature).

(7) Four-probe level controller (shortest probe andlongest probe are safety controls).

(8) Generator purge line (allows purging of thegenerator during operation).

(9) Purge control switches (auto-manual, auto-offlocated in the control panel or center).

(10) Purge alarm light (in control panel or center toindicate high or low level). Proper purging of the systemis useless unless you maintain the recommendedmaximum steam pressure.

9. Machine Supply Steam Pressure. Themaximum steam pressure at the generator should neverexceed the manufacturer's specifications. Excessivesteam pressures may cause the solution to solidify andmake it necessary to shut down the machine.

10. Solution Solidification. Excessive steampressure is not the only possible cause of solutionsolidification. Entering condensing water at too low atemperature, an excessive air leak, improperly adjustedcontrols, or power failure shutting the machine off sothat it cannot go through a dilution cycle may also causethis difficulty. Solidification will cause the machine tostop, but there will be no permanent damage to themachine. After the solution is desolidified, the machinemay be placed back in operation, but the cause of thedifficulty should be corrected.

11. A steam desolidification line is encased in thesolution heat exchanger of the machine. The procedurefor desolidification outlined below should be followedstep by step:

(1) Close the absorber purge valve and the purgesteam supply valve. This will isolate the machine fromthe purge unit and prevent air from entering themachine.

(2) Shut off the condensing water pump but leavethe main steam supply valve open. This allows thesolution to heat without vapor being condensed in thecondenser.

(3) Open the manual dilution valve which will allowchilled water to enter the solution circuit and dilute thesolution.

(4) Open the steam supply valve and steamcondensate return valve in the desolidification line.

(5) Start the solution pump and pump the solutionup to the generator; close the generator flow valve.Allow the solution to heat up in the generator; then openthe generator flow valve and allow the solution to drainback to the absorber. As it begins to liquefy, the solutionwill start to flow. This process may have to be repeatedseveral times before the solution has liquefied enough topermit the circulation.

(6) Put the machine back into operation by startingthe condensing water pump and purge unit.

(7) The reason for solidification should bedetermined and corrected.

You have completed desolidification and have theabsorption system operating properly. Let us now discussshutdown procedures.

12. Shutdowns. Each shutdown--daily, standby, andextended-requires proper “off” sequencing of the systemcomponents to avoid damage to the machine and to keepthe lithium bromide from solidifying.

13. Daily shutdowns. To stop a completely automaticsystem you must push the stop button. This willautomatically close the capacity control valve and purgevalve. All other components will operate forapproximately 7 minutes after this short period, themachine will shut down automatically. The followingprocedure is recommended for daily shutdown onautomatic machines with manual auxiliaries:

(1) Move the start switch to the OFF position.(2) Shut down the purge unit.• Close the absorber purge valve.• Close the purge steam supply valve.• Push the stop button on the purge control panel

to stop the purge pump.(3) Dilute the solution sufficiently to prevent

solidification during shutdown.• Open the manual dilution valve for the proper

length of time. The time will range from approximately2 to 5 minutes and must be determined by experience foreach machine.

• Close the manual dilution valve after the properinterval. This valve must not be left unattended duringthe dilution period since too long an interval will weakenthe solution and lengthen the recovery period when themachine is placed back in operation.

(4) Shut down the refrigerant and chilled watercircuit

• Shut down the refrigerant water pump.• Close the valve in the refrigerant pump

discharge line.• Shut down the secondary chilled water pump.(5) Shut down the condensing water circuit.• Shut down the condensing water pump.• Shut down other auxiliaries in this system such

as cooling tower, cooling tower fan, and auxiliary valves.(6) Close the main steam supply valve to shut off

the steam to the machine.(7) Shut down the solution pump. After the

solution has drained from the generator back to

33

the absorber, the solution circuit will be ready for startup.It is not necessary to close either of the solution valves.

14. Standby shutdown. This type of shutdown isused at an installation where it is not necessary to use themachine for cooling at irregular intervals during thewinter or off-cooling seasons. This procedure does notapply if freeing temperatures are expected in the machineroom. The procedure is the same for daily shutdownexcept for the following two steps:

(1) Dilution should be sufficient to insure thatsolidification of the solution will not take place at thelowest temperatures expected in the machine room.

(2) The final step in the procedure is to charge themachine with nitrogen.

• Connect the nitrogen tank to the nitrogencharging valve. On some systems, the alcohol chargingvalve is used as the connection for charging nitrogen intothe system.

• Set the pressure-reducing valve on the nitrogentank to 18 p.s.i.g. This is the maximum allowablepressure that may be used on the machine. Higherpressures will cause leakage at the pump seals.

• Open the nitrogen valve on the nitrogen tankand allow the nitrogen to enter the machine. Observethe pressure on the solution pump discharge gauge.When this gauge reads 3 to 5 p.s.i.g., close the nitrogenvalve and remove the nitrogen charging line.

15. Extended shutdown. When the machine is to beplaced out of service for an extended length of time, asduring the winter, there are many special services whichmay be required to protect the equipment from freezingtemperatures. The procedures are the same as for dailyshutdown except for the following additional services:

(1) The solution must be diluted enough to insureagainst solidification at the lowest expected temperaturesin the machine room. To do this, put the machinethrough three dilution cycles before it is shut down.

(2) Store the solution in the generator by closing thestrong valve and running the solution pump until thesolution is pumped from the absorber into the generator.Then close the diluted solution valve before shutting offthe solution pump.

(3) The machine is charged with nitrogen to preventair from getting into the machine as outlined in theprocedure for standby shutdown.

(4) Drain all the chilled water from the machineand other equipment. Leave all the drains open: exceptthe one from the machine proper.

(5) Drain all the condensing water from themachine and other equipment and leave the drains open.

(6) Drain the water from the purge condenser shellby opening the drain connection on the bottom of thepurge condenser.

(7) Drain all the water from the purge condensercoil by removing the tubing between the water jet pipingand purge condenser coil.

(8) Drain all the water out of the seal tank byopening the drain connection in the bottom of the waterseal tank.

(9) Drain all the water out of the water sea linesand the pump seal chambers by opening the petcocklocated in the line in the bottom of the pump sealchambers.

(10) Drain all the steam traps and steam drop legs.16. Most maintenance is performed while the

system is shut down. Let us now discuss maintenance ofabsorption air-conditioning systems.

8. Maintenance1. The maintenance procedures listed in this

section are carried out at time intervals listed in themanufacturers' service manuals. We will not set anytime interval because it varies with equipment models,and your particular SOP will outline this information.We will discuss annual maintenance because mostmanufacturers' handbooks list the same tasks to beperformed at that time.

2. Checking Vacuum. Before starting themachine, you should check it to see if air has leaked intothe unit while it was shut down. Open the valve in theline from the absorber to the manometer and determinethe pressure in the machine. Figure 32 illustrates amanometer reading. Take the temperature of themachine room and locate the corresponding pressure onthe chart in figure 33. If the pressure reading in themachine is more than 0.1 inch of mercury higher thanthe pressure located on the curve, then there is air in themachine. This should be noted on the daily log sheet. Ifthe condition recurs on the next two or three startups,the machine should be shut down as soon as possible andtested for leaks. Air leakage will cause corrosion insidethe machine, and over a period of time will result inserious trouble and shorten the life of the equipment.

3. Checking Mechanical Pump Seals. Themechanical pump seals, as shown in figure 34, should bechecked for leakage before starting the machine. Closethe petcocks in the water lines to the pump sealchambers. Observe the readings of the compoundpressure gauges in the water lines between the petcockand the pump seal chambers. If the gauge shows avacuum, this is

34

Figure 32. Absorber manometer.

an indication of a leaking seal. If only a small amount ofseal water has been lost, the leak is small and themachine may be placed in operation; but the seal shouldbe replaced at the first opportunity. If a large amount ofseal water has been lost, then the seal should be replacedbefore the unit is put into operation.

4. Flushing Seal Chamber. Flushing the sealchamber is recommended for lengthening the life of theseals. Approximately 15 minutes after the machine isstated and the solution has concentrated, drainapproximately 1 quart of water out of each seal chamberby use of drain petcocks located on each chamber. Thisis necessary to prevent the buildup of solutionconcentration in the chamber by the solution that mayleak past the seal faces. Make sure that the drain water isreplaced, since continually draining water would result ina loss of evaporator water.

5. Checking Water in Evaporator Sight Glass.Before starting the machine, the water level in theevaporator sight glass should be checked. If the waterlevel is the same as when the machine was shut down,the condition indicates that there is no leakage. If thelevel is higher, then chilled water has leaked back into themachine. The machine should not be started under theseconditions, since it is possible to lose the solution charge.Consult the instructions for the machine to cover thissituation.

6. Checking Absorber for Presence of Water.Turn on the light at the absorber bull's-eye. Look intothe absorber section through the inspection hole opposite

the light. No water should be visible. If water is visibleit has leaked into the section from the chilled water orseal water system. Under these conditions, the machineshould not be started since it is possible to lose thesolution charge. Consult the instructions for the machineto cover this situation.

7. Adding Octyl Alcohol to Solution. Once aweek, about 6 ounces of octyl alcohol should be added tothe solution circuit while the machine is running. Thiscleans the outside of the tubes in the generator andabsorber and improves their efficiency in transferringheat. The procedure is as follows:

(1) Pour about 8 ounces of octyl alcohol in a glasscontainer.

(2) Hold the container under the alcohol chargingconnection as shown in figure 35. The end of thecharging connection must be kept close to the bottom toprevent air from entering the machine.

(3) Slowly open the charging valve and observe thealcohol level as it is drawn into the machine. Close thevalve quickly so that the level of liquid remains above theend of intake tube to prevent air from entering themachine.

8. If the alcohol is drawn rapidly into the chargingconnection, it indicates that the conical strainer andsolution spray header are clean. A progressive decrease inthe rate at which alcohol is drawn shows that these unitsare becoming clogged. If alcohol is not drawn into thecharging connection, it is an indication that the conicalstrainer is clogged. In this case, the conical strainershould be removed and cleaned at the next shutdown. Ifthe condition still persists, it will be necessary to removeand clean the solution spray header.

9. Cleaning Purge Steam Jet. This is animportant part of the maintenance since the purge unitmust be kept in good operating condition to maintainefficiency of the machine. The following procedures willapply to both single- and two-stage steam jets:

(1) Check to be sure that the absorber purge valve(item 1 in fig. 36) is closed.

(2) Close the purge steam supply valve (item 2).(3) Remove the steam jet cap.(4) Use a piece of thin wire through the top of the

steam jet to loosen any dirt in the nozzle.(5) Open the purge steam supply valve to blow out

loosened dirt and then close the valve.(6) Replace the steam jet cap.10. Checking Evaporator Water Circuit for

Lithium Bromide. While the quantity of solution doesnot formally change, a high boiling level in the generatormay force solution into the evaporator water circuit. Asolution test kit must be

35

Figure 33. Pressure and temperature curve.

Figure 34. Seal water system.

36

Figure 35. Octyl alcohol charging.

used to detect and measure the percentage of lithiumbromide in the evaporator water. The test kit containsthree bottles labeled No. 1, No. 2, and No. 3. No. 1contains an indicator solution, No. 2 contains silvernitrate, and No. 3 is a standard solution of lithiumbromide. The test kit is used as follows:

(1) Place ten drops of evaporator water sample fromthe system into a clean bottle.

(2) Add three drops of No. 1 to the sample.(3) Count the number of drops of No. 2 solution

necessary to turn the sample a permanent red. Recordthe number of drops of No. 2 used.

(4) Place ten drops of the standard solution, No. 3,in a clean bottle.

(5) Add three drops of No. 1 solution.(6) Count the number of drops of No. 2 necessary

to give a permanent red. Record the number of drops.11. The standard sample of lithium bromide is a

1-percent solution. By comparing the number of drops ofsolution No. 2 required to turn the

Figure 36. Steam jet purge.

37

Figure 37. Manual dilution.

evaporator water sample red with the number of dropsrequired to turn the standard red, the percentage oflithium bromide can be determined. If the evaporatorwater sample requires less of No. 2 than the standard,then it contains less than 1 percent of lithium bromide.If the test shows the lithium bromide content of theevaporator water to be greater than 1 percent, it shouldbe reclaimed.

12. Reclaiming Solution. The lithium bromide isreclaimed by passing evaporator water into the solutioncircuit while the machine is in operation. The length oftime required for reclamation will be determined by theamount of salt in the evaporator water circuit. Thecapacity of the machine will be partly reduced during thisperiod. The process should be continued until the testshows less than one-half of 1 percent. The procedure forreclaiming solution is as follows:

(1) Crack the manual dilution valve, item A infigure 37, and feed water slowly into the solution circuit.

(2) Check the boiling level through the generatorbull's-eye sight glass. If the light cannot be seen, theboiling level is too high. Bring the boiling level down byslightly closing the dilution valve until the light can beseen.

(3) Continue the process until the test shows lessthan one-half of 1 percent. This may take anywherefrom a few hours to several days, depending on theamount of salt in the evaporator water circuit.

13. Annual Maintenance. Before annualmaintenance is started, the machine should be shut downand charged with nitrogen as outlined in the procedurefor extended shutdown. The following paragraphs arearranged in the same sequence as the work wouldnormally be performed.

14. Cleaning lithium bromide solution. To clean thelithium bromide solution, it must be removed from themachine as follows:

(1) Open the valves in the solution line to and fromthe generator; this will drain the solution into theabsorber section.

(2) Attach a suitable rubber hose to the dischargeconnection of the solution pump.

(3) Close the valves in the solution to and from thegenerator and close the valve in the vapor condensatereturn line. This isolates the generator from theabsorber.

(4) Start the solution pump and pump the solutioninto drums. The pump should shut off automaticallywhen the absorber is empty.

(5) Remove the plug in the solution inductor todrain the piping below the absorber.

NOTE: The solution in the drums should beallowed to stand for 2 or 3 days to allow the dirt to settle.

15. Cleaning absorber sight glass. The bull's-eyesight, evaporator tank sight and absorber reflex glassesshould be carefully removed and cleaned. Crackedglasses or those with collected foreign matter that cannotbe cleaned should be replaced. New gaskets should beused when the glasses are reinstalled.

16. Cleaning solution strainer. The procedure forremoving and cleaning the conical solution strainer is asfollows:

(1) Remove the nuts holding the solution supplyheader.

(2) Remove the nuts and bolts in the flangeconnection to the solution piping.

(3) Remove the solution supply header. Figure 38illustrates the solution supply header.

(4) Remove the bolts holding the blank flange onthe solution supply header.

(5) Carefully remove the strainer and clean it byflushing it with water.

(6) Replace the strainer and use a new gasket underthe blank flange. Be sure that the flange faces are cleanso that the flange will seal properly when bolted back inplace. Do not replace the supply header until the sprayheader has been removed and cleaned.

17. Cleaning solution spray header. If the supplyheader has not been removed, proceed with

Figure 38. Solution supply header.

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Figure 39. Solution sprayheader.

steps (1), (2), and (3) in the preceding paragraph. Whenthis has been done, remove the solution spray header,being extremely careful that the spray nozzles do notstrike the sides of the opening. Clean it by flushing.Any nozzles that are not clear should have the nozzle capremoved and cleaned individually. The old gasketmaterial should be thoroughly removed from the sprayheader and a new gasket used when it is ready forreassembly. A solution spray header is shown in figure39.

18. To install the spray header, slide it back throughthe opening until it is 2 inches from the far end.Remove the plug from the absorber at the end oppositeto the header opening. Insert a rod through this hole andlift the end of the spray header so as to guide it throughthe last couple of inches into its proper position. Installthe supply header, using a new gasket. Replace the plugin the far end of the absorber.

19. Cleaning chilled water spray header. The chilledwater spray header is removed and cleaned by the sameprocedure as just outlined. However, even more caremust be exercised in handling this header since it ispossible not only to damage the nozzles but, if the headeris allowed to tip, the eliminator plates may be bent.These are thin plates like the fins in an automobileradiator which when bent will lose their effectiveness.Clean off the old gasket material and install a new gasketbefore replacing the header on the machine. A plugmust be removed from the opposite end as before so thata guide rod can be used on the far end of the header.

20. Cleaning primary purge connections on absorber.Clean the primary purge connections on the absorber byremoving the plugs in the T connections at the primarypurge line and cleaning the line with a wire or nylonbrush. Only a small amount of water should be used towash out this area. Replace the plugs after the cleaningoperation is completed.

21. Inspection of vacuum type valves. All vacuum typevalves should have their bonnets removed and thediaphragms checked for cracks or signs of wear whichmight indicate a future failure. Following is a list of thedifferent vacuum type valves used in an absorptionsystem:

Purge valvesSolution valveManual dilution valveChilled water makeup valveVapor condensate return valveAbsorber manometer valveSolution charging valveChilled water valves22. Although proper service will cause some

diaphragms to last longer, it is considered goodmaintenance practice to replace all diaphragms every 2years. This helps to prevent a breakdown or aninterruption of service during the cooling seasons.

23. Checking generator sight glasses. The generatoroverflow sight glass and the generator bull's-eye sightglasses should be removed and cleaned. Glasses that aredamaged should be replaced. New gaskets should alwaysbe used when the glasses are reinstalled.

24. Cleaning water seal system. The entire water sealsystem should be inspected and cleaned according to thefollowing procedure:

(1) Open the drain connections on the bottom ofthe water seal tank and drain the water.

(2) Open the petcocks on the bottom of the pumpseal chambers and drain the water from the lines andchambers.

(3) Disconnect the water seal lines between thewater seal tank and the pump seal chambers and cleanthem by reverse flushing with water. Use compressed airto blow out the lines after flushing.

(4) Inspect and clean all the pipe connections.(5) Clean the purge tank and flush it to remove the

loosened dirt.(6) Reinstall the water seal lines.25. Cleaning absorber and condenser tubes. The

absorber and condenser tubes should be cleaned at leastonce a year. More frequent cleaning may be necessary asindicated by a steady rise in vapor condensatetemperature during the season. A steady decrease intemperature of the condensing water leaving the machinemay also indicate scaling. This condition may be furtherconfirmed by inspection of the thermometer well in thecondenser water line leaving the machine. The presenceof scale here is associated with scaling in the tubes.Cleaning should be done as follows:

(1) Remove both headers from the absorber andcondenser.

(2) Inspect the tubes to determine the type of scale.(3) Soft scale may be removed by cleaning with a

nylon bristle brush. Metal brushes of any kind whichmight scratch the surface must never be used. Hardscale which cannot be removed

39

with a brush will require treatment with suitablechemicals.

26. Cleaning condensing water system. Theprocedures for cleaning the condensing water system ofan absorption refrigeration system are similar to theprocedures used to clean the condensing water systemson compression refrigeration systems.

27. Cleaning salinity indicator. The salinity indicatorshould be removed and the electrodes cleaned ofaccumulated deposits.

28. Vacuum Testing Machine for Leaks. Aftercompleting the maintenance work, the machine shouldnext be tested for leaks according to the followingprocedures.

(1) Close all valves except the vapor condensatevalve which must be left open.

(2) Start the water jet on the purge unit and openthe absorber purge valve and the evacuation valve.Operate the purge unit until a vacuum of at least 25inches of mercury is read on the manometer. Recordthis reading.

(3) Shut down water jet and close the valves.(4) Check the manometer vacuum 24 hours later.

The maximum allowable loss is one-tenth of an inch ofmercury in 24 hours. If the loss is within limits, thencharge the machine with solution. A machine that doesnot meet the vacuum requirements must be tested forleaks with a halide leak detector.

29. Halide Leak Detector Test. The proceduresfor testing with the halide leak detector are as follows:

(1) Make sure that all valves are closed except thevapor condensate valve.

(2) Charge the machine with Refrigerant-12 to apressure of 5 p.s.i.g. Use the refrigerant type chargingvalve on the absorber. Read the charging pressure in themachine on the solution pump pressure gauge.

(3) After charging with Refrigerant-12, the machineshould be further charged to 18 p.s.i.g. with nitrogen,using the procedure previously given under Extendedshutdown.

(4) Test the machine for leaks with a halide leakdetector. Stop all the leaks that are found.

(5) Perform another vacuum test to determine thatthe machine is now satisfactory.

30. Charging the Machine. After maintenance iscompleted and the machine passes a satisfactory vacuumtest, the machine should be charged with solution. Themachine must be kept charged with solution at all timesexcept while maintenance is being done. Storage drumsused to hold the solution should be moved as little aspossible so as not to disturb dirt which

Figure 40. Solution charging.

has settled to the bottom. Figure 40 illustrates themethod of solution charging.

(1) Start the water jet on the purge unit and openthe purge valve on the absorber.

(2) Continue purging until a vacuum reading of 25inches of mercury is obtained on the manometer. Closethe valves and shut off the jet when the vacuum issatisfactory.

(3) Connect the hose to the solution charging valveand place the other end of the hose into the drum ofsolution. Do not let the hose touch the bottom of thedrum since this would draw up dirt that had settled there.

(4) Open the solution charging valve and allow thesolution to enter the machine.

(5) After all of the solution has been transferredinto the machine, close the solution valve in the linefrom the generator and open the solution valve in theline to the generator.

(6) Start the solution pump which will pump all thesolution up to the generator. When the pump shuts off,close the valve in the line to the generator. This last stepis necessary because all of the solution should be storedin the generator.

(7) If the machine is to remain out of service, thenit should be charged with nitrogen as previously outlined.

31. Troubleshooting. Troubleshooting andcorrection are two of your most important duties. Wehave discussed the operation and service that youperform on absorption systems. This information,coupled with that in tables 1-18, should give you theknowledge you need to carry out your assigned tasks.

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TABLE 11

TABLE 12

TABLE 13

41

TABLE 14

TABLE 15

TABLE 16

TABLE 17

TABLE 18

42

Review Exercises

The following exercises are study aids. Write youranswers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the text. Do not submit your answers for grading.

1. While you are performing your hourly check ofthe absorption system, you notice that thecondenser waterflow has dropped off and thatthe system is operating at a reduced capacity.What component should you troubleshoot andwhere is the component located? (Sec. 5, Par.2)

2. The refrigerant used in this system is_____________________ and theabsorbent is ______________. (Sec. 5, Par.3)

3. What will occur within the system when heat isnot supplied to the generator? (Sec. 5, Par. 5)

4. (Agree)(Disagree) The heat exchanger heats thestrong solution. (Sec. 5, Par. 5)

5. During a routine inspection you find that thesupply air pressure to the chill water thermostatis 3 p.s.i.g. What component is affected? Howdoes this component affect the operation of thesystem? (Sec. 5, Pars. 6 and 7)

6. A 2° chilled water temperature change will causethe branch line pressure to change_____________ p.s.i.g. (Sec. 5, Par. 7)

7. What will occur if the feeler bulb of theconcentration limit thermostat is broken? (Sec.5, Par. 8)

8. The plant operator submits the followingcomplaint:(1) The chill water temperature is 57° F. (The

design temperature is 45° F.)(2) The off-run-start switch is in the RUN

position.(3) The solution pump is off and the last

discharge pressure reading was 36 p.s.i.g.

What has occurred within the system to cause ashutdown? How do you restart the unit? (Sec.5, Pars. 9 and 10)

9. Why are the solution and chilled water pumpsequipped with mechanical seals? (Sec. 5, Par.14)

10. (Agree)(Disagree) The float control in thesolution pump water seal tank controls makeupwater to the tank automatically. (Sec. 5, Par. 15)

11. The primary difference between daily startupand startup after standby shutdown is that__________________. (Sec. 6, Par. 3)

12. The evaporator pump is surging. What causedthis surging? (Sec. 7, Par. 3)

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13. A solution level in the absorber of two-thirds(Sec. 7, Par. 4)

14. When is the solution boiling level in thegenerator set? (Sec. 7, Par. 5)

15. What will occur when air is being handled bythe purge unit? (Sec. 7, Par. 7)

16. Excessive steam pressure will cause_____________________. (Sec. 7, Par. 9)

17. Where would you connect the nitrogen tank ifthe system did not have a nitrogen chargingvalve? (Sec. 7, Par. 14)

18. To dilute the solution for extended shutdown,you must put the system through______________ dilution cycles. (Sec. 7,Par. 15)

19. How can you determine whether air has leakedin the machine during shutdown? (Sec. 8, Par.2)

20. Air will cause the insides of the machine to(Sec. 8, Par. 2)

21. How do you check a mechanical pump seal forleaks? (Sec. 8, Par. 3)

22. Why should you flush the seal chamber afterstartup? (Sec. 8, Par. 4)

23. An increased water level in the evaporator aftershutdown indicates that__________________. (Sec. 8, Par. 5)

24. Why is octyl alcohol added to the solution?(Sec. 8, Par. 7)

25. How would you correct the followingmalfunction? The octyl alcohol charging valveis open but the alcohol is not being drawn intothe machine. What would you do if thissituation occurred frequently? (Sec. 8, Par. 8)

26. The following complaint has been received atyour shop. The steam jet purge unit on anabsorption system is operating but is not purgingair that is present in the absorber. What is themost probable cause and how would you correctit? (Sec. 8, Par. 9)

27. Bottle number 2 in the solution test set contains_______________. (Sec. 8, Par. 10)

28. How many drops of indicator solution do youadd to the solution sample? (Sec. 8, Par. 10)

29. The standard sample (bottle No. 3) is a________________ percent solution. (Sec.8, Par 11)

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30. During an evaporator water solution test, moresilver nitrate was needed to turn the sample redthan the standard solution. What does thisindicate? How is this situation remedied? (Sec.8, Pars. 10 and 11)

31. What determines the length of time needed toreclaim the evaporator water? (Sec. 8, Par. 12)

32. How long does it take for the dirt in thesolution to settle out when the solution is placedin drums? (Sec. 8, Par. 14)

33. How is the conical strainer cleaned? (Sec. 8,Par. 16)

34. How is the purge connection on the absorbercleaned? (Sec. 8, Par. 20)

35. (Agree)(Disagree) The diaphragm is a vacuumtype valve should be replaced yearly. (Sec. 8,Par. 22)

36. The operating log shows a steady increase invapor condensate temperature. Whatmaintenance is required? (Sec. 8, Par. 25)

37. How is soft scale removed from condensertubes? (Sec. 8, Par. 25)

38. What is the maximum allowable vacuum lossduring a vacuum leak test? (Sec. 8, Par. 28)

39. Which refrigerant is added to the system toperform a halide leak test? (Sec. 8, Par. 29)

40. List at least three possible causes of lithiumbromide solidification at startup. (Sec. 8, table11)

41. How can you make sure that a seal is leaking?(Sec. 8, table 12)

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CHAPTER 3

Centrifugal Systems

FEW PEOPLE realize the importance of the refrigerationspecialist in this age of aerospace weapons systems. Forthem, refrigeration has nothing to do with launching amissile and reaching the moon. However, we know thatwithout control of the environment of a launch complexthe military goals of defense and space conquest wouldnever be achieved.

2. The centrifugal refrigeration system is oftenused in such weapons systems as Titan, Bomarc, andSAGE. In this chapter we will discuss the operation ofthis system, the complete refrigeration cycle, eachcomponent of the unit, and the general maintenancerequirements.

9. Refrigeration Cycle1. The centrifugal system uses the same general

type of compression refrigeration cycle used on othermechanical systems. Its features are:

• A centrifugal compressor of two or more stages.• A low-pressure refrigerant known as Refrigerant-

11. Approximately 1200 pounds of refrigerant arerequired for fully charging a centrifugal machine.

2. An economizer in the liquid return from thecondenser to the evaporator acts as the expansion device.You can compare the economizer to the high side float(metering device) used on older model refrigerators. Theuse of this piece of equipment reduces the horsepowerrequired per ton of refrigeration cycle. This increase inefficiency is made possible by using a multistageturbocompressor and piping the flash gas to the secondstage.

3. A schematic of the centrifugal cycle is shown infigure 41. We will begin the cycle at the evaporator.The chilled water flowing through the tubes is warmerthan the refrigerant in the shell surrounding the tubes,and heat flows from the chilled water to the refrigerant.This heat evaporates the refrigerant at a temperaturecorresponding to the pressure in the evaporator.

4. The refrigerant vapors are drawn from theevaporator shell into the suction inlet of the compressor.

The suction vapors are partially compressed by the first-stage impeller and join the flash gas vapor coming fromthe economizer at the second-stage impeller inlet. Therefrigerant gas discharged by the compressor condenseson the outside of the condenser tubes by giving up heatthrough the condenser tubes to the cooler condenserwater. The condensing temperature corresponds to theoperating pressure in the condenser.

5. The liquefied refrigerant drains from thecondenser shell down through an inside conduit into thecondenser float chamber. The rising refrigerant level inthis chamber opens the float valve and allows the liquidto pass into the economizer chamber. The pressure inthe economizer chamber is approximately halfwaybetween the condensing and evaporating pressures:consequently, enough of the warm liquid refrigerantevaporates to cool the remainder to the lowertemperature corresponding to the lower pressure in theeconomizer chamber. This evaporation takes place byrapid "flashing" into gas as the liquid refrigerant passesthrough the float valve and the conduit leading into theeconomizer chamber. The flashed vapors pass througheliminator baffles and a conduit to the suction side of thesecond stage of the compressor.

6. The cooled liquid then flows into theeconomizer float chamber located below the condenserfloat chamber. The rising level in the economizer floatchamber opens the float valve and allows the liquidrefrigerant to pass into the bottom of the cooler. Sincethe evaporator pressure is lower than the economizerpressure, some of the liquid is evaporated (flashed) tocool the remainder to the operating temperature of theevaporator. These vapors pass up through the liquidrefrigerant to the compressor suction. The remainingliquid serves as a reserve for the refrigerant continuallybeing evaporated by the chilled water. The cycle is thuscomplete.

7. Now that you understand the completerefrigeration

46

Figure 41. Centrifugal cycle.

Figure 42. Compressor cutaway.

cycle, let us study the compressor in more detail.

10. Centrifugal Compressor1. A cutaway view of the compressor is shown in

figure 42. The easiest way to understand centrifugalcompressor operation is to think of a centrifugal fan.Like the fan, the compressor takes in gas at the end (inline with the shaft) and whirls it at a high speed. Thehigh-velocity gas leaving the impellers is converted to apressure greater than the inlet. At normal speed, with R-11, the suction temperature is 65° F. below thetemperature of condensation. At maximum speed, thecompressor will produce a suction temperature ofapproximately 85° F. below the condensing temperatureof R-11. Changing the speed of the compressor variesthe suction temperature.

2. The compressor casing and the variousstationary passages inside the compressor shaft are madeof hard steel with keyways provided for each impeller.The impellers are of the built-up type. The hub disc andcover are machined steel forgings. The blading is sheetsteel formed to curve backward with respect to thedirection of rotation and is riveted to the hubs andcovers. After assembly, the wheels are given a hot-dipped lead coating to reduce corrosion damage. Therotor

47

Figure 43. Bearing assembly.

assembly, consisting of the shaft and impellers, runs intwo sleeve type bearings.

3. In figure 43 a thermometer is inserted in top ofeach bearing cover (1) for indicating temperature. Eachbearing also has two large oil rings (2) to insurelubrication. The upper and lower bearing liners (3) areheld in place by the upper and lower bearing retainers (4).

4. Brass labyrinths (5) between stages and at theends of the casing restrict the flow of gas between stagesand between the compressor casing and bearingchambers.

5. In operation, the pressure differential across eachimpeller produces an axial thrust toward the suction endof the compressor. This thrust is supported by a"kingsbury" thrust bearing at the suction end of the shaft.

6. Compressor Lubricating System. The entireoiling system is housed within the compressor casing andthe oil is circulated through cored opening, drilled pages,and fixed copper fines. This eliminates all of the usualexternal lines and their danger of possible rupture,damage, or leakage. All of the oil for the lubricatingsystem is circulated by a helical gear pump, shown infigure 44, which is submerged in the oil reservoir. Thesimple, positive drive insures ample oil for pressurelubricating and cooling all journal bearings, thrustbearings, and seal surfaces. The reservoir which housesthe oil pump is an integral part of the compressor casingand is accessible through a cover plate on the end of thecompressor. Circulating water cooling coils are fitted tothe cover plate to maintain proper oil temperature.

7. In general, the lubricating system (shownschematically in fig. 45) consists of the gear type oil

pump, driven from the main compressor shaft andsupplying oil through various connections and passagesfor the thrust bearing, the two shaft bearings, the oilpump worm gear drive, and for the shaft seal-with thenecessary gauges and control valves to permit the systemto operate automatically.

8. The oil pressure or feed circuits are as follows,according to figure 45:

• When the compressor starts, the pump (1) startsto circulate oil, which is supplied first entirely to thethrust bearing (3).

• After passing through the thrust bearing, theoiling system divides into two paths known as "A" circuitand "B" circuit.

9. In the first path, the oil flows through thestrainer (29) and the proper orifices to the pump gear (2)and to the rear shaft journal bearing (4). Since thethrust, rear journal bearing, and worm drive for the oilpump are all located above the oil pump chamber, thereturn oil merely drops back into the pump chamberfrom these parts.

10. In the second path, oil flows through the checkvalve (5) and filter (7) to actuate the shaft seal (8) andsupply the front shaft journal bearing (9). Since part ofthe oil passes out through the front of the seal toatmospheric pressure, various valves are required in thesupply lines as well as in the lines returning oil to thepump chamber. The check valve (5) does not openduring compressor startup until the pump pressurereaches 8 p.s.i.g. After the valve (5) opens, the flow ofoil is as described previously. If the seal oil reservoir (6)is not full, a small part of the oil passes through theorifice (28) to fill the reservoir. Oil under pressure to theseal

Figure 44. Compressor oil pump.

48

Figure 45. Compressor oil system schematic.

expands the seal bellows to move the stationary seal backagainst its stop, allowing the oil to pass through the sealin two directions: (1) inside the compressor and (2) tothe atmospheric side of the shaft seal.

11. The oil passing to the compressor (vacuum) sideof the seal flows to the front journal bearing (9), throughtwo small holes in the inner floating seal ring (12) -whichis located in the seal housing--to prevent unnecessaryflow of oil from the vacuum side of the seal. Thebearing overflow drops to the bottom of the bearingchamber (10), draining back to the oil pump chamberthrough the proper passage in the manifold (18).

12. The oil passing to the atmosphere is restricted byfloating rings between the stationary seal and rotating sealhubs and between the housing cover and the rotating sealhub. Most of it passes directly to the atmospheric floatchamber (13). The water-jacketed seal housing cover(11) cools this oil and minimizes the refrigerant loss fromit. A small amount of oil passes the seal rings and isreturned to the atmospheric float chamber (13) through aconnection (30). From the float chamber, the oil goes

through the automatic oil stop valve (16), up to thebearing chamber (10), and returns through the manifoldto the oil pump chamber along with the oil overflowfrom the front bearing. Oil returns from the atmosphericfloat chamber since the pressure in the bearing chamberis always below atmospheric. This pressure, beingequalized with the compressor suction through the rearshaft labyrinth, is always a vacuum during operation.From the bearing chamber, the oil flows by gravitythrough the manifold (18), to the oil pump chamber.The automatic stop valve (16) is provided to prevent flowof refrigerant vapor from the machine in case thepressure inside the machine during shutdown rises aboveatmospheric. The valve is set to open at approximately 8pounds and is actuated by an oil pressure line taken fromthe oil pump discharge and, therefore, opens immediatelyafter the compressor is started. Valve 16 also preventsoutside air from entering the machine when the machinepressure is below atmospheric. This valve is necessarybecause the atmospheric float valve (14) is designed forlevel control only and is not a stop valve. Valve 17 is

49

Figure 46. Compressor oil heater.

the oil pressure regulator. It is actuated by pressure "backof seal" through line 15 and controls oil pressure byreturning excess oil back to the oil pump chamber.

13. Oil pressure gauges 22 and 23 on the controlpanel indicate the seal oil reservoir pressure and thepressure back of seal respectively. When the seal oilreservoir is full, gauge 22 indicates the pressure on theseal bellows. Gauge 23 indicates the pressure in the spacebetween the seal and the inner floating ring or back ofseal pressure which controls valve 17.

14. The air vent and vacuum breaker (27) admitsatmospheric pressure during shutdown to the seal oilreservoir to maintain a head of oil on the seal. Itoperates as a gravity check valve.

Figure 47. Shaft seal assembly.

The oil heater (31) heats the oil during shutdown toprevent excessive absorption of refrigerant by the oil. Aflow switch located in the water supply to the oil coolermanifold automatically turns the heater on when thewater supply is shut off by hand, and cuts the heater offwhen the water is turned on. A schematic diagram ofthe oil heater is shown in figure 46. The oil cooler (19)cools the oil as it is returned to the pump chamber duringoperation. Bearing thermometers 24 and 25 indicate thetemperature of the shaft bearings. Oil rings 20 and 21--also shown in figure 45-bring additional oil from thebearing wells to the shaft. Relief valve 26 in the oilpump discharge line relieves any unusually high pressurethat may occur accidentally, and thus protects the systemagainst any damage.

15. Compressor Shaft Seal. A shaft seal isprovided where the shaft extends through the compressorcasing. The seal assembly is shown in figure 47.

16. The seal is formed between a ring, called therotating scaling seat which is fitted against a shoulder onthe shaft, and stationary sealing seat which is attached tothe seal housing through a flexible member or bellowsassembly. The contact faces on these seal seats arecarefully machined and ground to make a vacuum-tightjoint when in contact. A spring called the seal springmoves the stationary seal seat into contact with therotating seal seat to make the proper seal when thecompressor is shut down. A floating ring is locatedbetween the hub of the stationary sealing seat and thehub of the rotating sealing seat. A seal oil reservoir andfilter chamber is attached to the compressor housingabove the seal to provide oil to maintain a head of oil tothe seal surfaces

50

Figure 48. Diagram of compressor seal end.

during shutdown periods. The shaft seal consists of twohighly polished metal surfaces which are held tightlytogether by a spring during shutdown, but are separatedby a film of oil under pressure during operation. Thepositive supply of oil from the oil pump during operationand from the seal reservoir during shutdown prevents anyinward leakage of air or outward leakage of refrigerant.In addition, the low oil pressure safety control willautomatically stop the compressor if the oil pressure tothe seal falls below a safe minimum. Figure 48 shows acutaway diagram of the seal installed on the seal end ofthe compressor.

17. Lubricant. A high-grade turbine oil, such asDTE heavy medium or approved equal, is the type of oilrecommended for centrifugal compressor usage. To besure of specifications on grade and type of oil to use, it is

advisable to refer to the manufacturer's maintenancemanual.

18. If a machine is to be started for the first time orif all the oil has been drained from the unit, thefollowing lubrication procedures are recommended:

• The machine pressure must be atmospheric.• Remove the cover on the front bearing at the

coupling end of the compressor and pour 1 gallon of oilinto the front bearing level.

• Fill the seal oil pressure chamber by removingthe cover.

• Remove the cover from the rear bearing andpour oil into the chamber until the indicated height isreached as recommended on the pump chamber plate.

• Fill the atmospheric float chamber through

51

the connection on the side of the chamber until oilshows in the sight glass.

• Pour a small amount of oil into the thrustbearing housing by removing the strainer cap and pouringoil into the strainer.

Under normal operating conditions, the followinglubrication procedures are recommended:

• Replace the oil filter regularly, depending on thelength of operation and the condition of the filter.

• If at any time some oil is withdrawn from themachine, replace with new oil.

• Clean and inspect the strainer in the thrustbearing at least once a year. Replace the complete oilcharge at least once a year.

• After shutdown periods of more than a month,remove the bearing covers and add 1 quart of oil to eachbearing well before starting.

19. To drain the oil system, allow the machine towarm up until the temperature is approximately 75° F.The machine must be at atmospheric pressure. Drain thepump chamber by removing the drain plug. Replace theplug, then drain the atmospheric float chamber in thesame manner. By draining these two chambers,practically all of the oil is removed. The oil left in thebearing wells and seal reservoir is useful for keeping thebearing in satisfactory condition and as a sealing oil.

20. CAUTIONS: To keep the machine in the bestoperating condition, the following cautions must beobserved:

• The electric heater in the oil pump chambermust be turned on during shutdown periods and must beturned off when the cooling water is turned on.

• Do not overcharge the system with oil. The oillevel will fall as the oil is circulated through the system;but under normal operation, the oil level will increaseapproximately 7 percent in volume as the refrigerantbecomes absorbed in it. The oil level in the machine willbe approximately one-half glass.

• Oil can be added to the filling connection on theside of the atmospheric float chamber only while themachine is in operation and the atmospheric return valveis open.

21. Now that you have a proper knowledge ofcompressor operation, let's discuss the type of drive forthe compressor.

11. Compressor Gear Drive1. The gear drive is a separate component mounted

between the compressor and electric motor. The gearsare speed increasers required to obtain the propercompressor speed through the use of standard speed

motors. The gears are of the double helical type, properlybalanced for smooth operation, and pressure lubricated.The gear wheel and pinion are inclosed in an oiltightcase, split at the horizontal centerline. Lubrication isfrom the gear type oil pump. The unit has an oil levelsight glass, a pressure gauge, and an externally mountedoil strainer and oil cooler. A diagram illustrating the gearparts is shown in figure 49.

2. Lubrication. A good gear oil must be used forthe lubrication of high-speed gears. The oil must be keptclean by filtering, and filters changed as often as possible.The temperature of the oil should be kept within therange of 130° F. to 180° F. Water cooling should be usedwhenever necessary to keep the temperature within theselimits.

3. Type of Oil. The best grade of oil to use on agear depends on journal speeds, tooth speeds, andclearances. In general, it is better to use an oil too heavythan one too light. The gears will be somewhat warmer,but the heavier oil will take care of higher temperature ifit is not more than a few degrees. The heavier oil israted at 400 to 580 seconds Saybolt viscosity at 100° F.

4. Water Cooling of Gears. The gears are watercooled by circulating water through water jackets cast inthe ends of the gear casing or by means of either aninternal or an external oil cooler. This system isconnected to a supply of cool, clean water, at a minimumpressure of 5 pounds. A regulating device must beinstalled in the water supply line. The discharge lineshould have free outlet without valves to avoid possibilityof excessive pressures on the system. Piping must bearranged so that all the water can be drained or blownout of the water jackets or cooler if the unit is to besubjected to freezing temperatures.

5. Inspection. Inspect to see that both the drivingand driven machines are in line. If you are not sure thatalignment is correct, check this point with gauges. Tryout the water cooling system to see if it is functioningproperly. When starting, see that you have sufficient oilin the gear casing and that the oil pump gives requiredpressure (4 to 8 pounds). When the temperature of theoil in the casing reaches 100° F. to 110° F., turn on thewater cooling system. Add sufficient oil from time totime in order to maintain the proper oil level. Neverallow the gear wheel to dip into the oil.

6. Regular cleaning of the lubrication system andtests of the lubricant are essential. Clean the strainer atleast once a week and more often if necessary. Themanufacturer recommends that the gear case should bedrained and be completely cleaned out every 2 to 3months. Refill with new filtered oil. Between oilchanges, samples of oil

52

Figure 49. Gear drive components.

should be drawn off and the oil checked. If water ispresent, the water should be drawn off. If there is aconsiderable amount of water in the oil, remove all oiland separate the water from the oil before it is usedagain.

7. Repair. All working parts of the gear drive areeasily accessible for inspection and repair except the oilpump. If you should have to dismantle the gears, youmust take precautions to prevent any damage to gearteeth. The slightest bruise will result in noisy operation.When the gears are removed, place them on a clean clothplaced on a board and block them so that they cannotroll off. Cover the gears with a cloth to protect themfrom dust and dirt.

8. Bearing shells, oil slingers, etc., are marked andshould be returned to their proper places. Gaskets areused between the oil pump bracket and oil pump andunder handhole covers. All parts must be clean beforereassembly. Make sure that no metal burrs or cloth lintis present on any part of the unit. Coat faces of flangeswith shellac before bolting them together. A thin coat ofshellac on the bearing supports will prevent oil leaks atthese points. Before final replacement of the cover,make a careful inspection to see that all parts are properlyplaced and secured.

9. Worn bearings must be replaced immediatelybecause they will cause the gears to wear. Bearings areinterchangeable, and when new bearings

53

are installed the gears are restored to their original centerdistance and alignment. It is not recommended torebabbit bearings, for the heat required to rebabbit thebearings will cause some distortion of the bearing shell.Do not renew or scrape one bearing alone, but alwaysrenew or scrape in pairs; this will help eliminate toothmisalignment. Do not adjust bearing clearances byplaning the joint, thereby bringing the halves closertogether, since trouble will result.

10. The oil pump is a geared type. During assembly,care must be taken to see that the paper gasket betweenthe pump body and bracket is of the proper thickness. Agasket that is too thick will reduce the capacity and causefailure in oil pressure, while a too thin gasket will causean excessive load to be thrown on the gears, resulting inwear and destruction of the gears. Writing paper makes agood gasket when shellacked in place. Never use arubber gasket on any oil joint. "Cinch" fittings are usedon all pipes connected to the oil pump bracket; use thistype on all replacements. Threaded fittings may causethe bracket to be pulled out of line, causing noisyoperation and wear on gears. Couplings should not bedriven on or off the gear or pinion shafts, sincehammering is liable to injure both surfaces. Provisionshave been made for using a jacking device for putting onor removing couplings from shafts.

11. Gear tooth contact and wear should beuniformly distributed over the entire length of both gearand pinion helixes. If heavier wear is noted on anyportion of the helixes or any part of the tooth face, itmay indicate improper setting of the gear casing,misalignment of connecting shafts, vibration, excessive orirregular wear on the bearings, or poor lubricant. Shouldgear teeth become damaged during inspection oroperation, remove burrs by use of a fine file or oil stone.Never use these tools to correct the tooth contour.Misalignment, poor lubrication, and vibration can causepitting of tooth surfaces or flaking of metal in certainareas of the gear. If this happens, check alignment andremove all steel particles. Check the manufacturer'smaintenance manual for specific maintenance proceduresand instructions.

12. You now understand the drive system for thecompressor, but we must learn how the drive is coupledto the motor and the compressor.

12. Couplings1. The couplings used to connect the motor to the

speed-increasing gears and from the gears to thecompressors are self-alining coupling. They are of theflexible geared type, consisting of two externally gearedhubs that are pressed on and

Figure 50. Mounting coupling on shaft.

geared to the shaft. These hubs are inclosed by a two-piece externally geared floating cover which functions asa single unit when the halves are bolted together. Thecover is supported on the hub teeth during operation. Aspacer or spool piece is used with the cover for thecompressor coupling. The hub teeth and cover teeth areengaged around the complete circumference, and thecover and shafts revolve as one unit. The cover and eachshaft is free to move independently of each other withinthe limits of the coupling, thus providing for reasonableangular and parallel misalignment as well as end float.The amount of misalignment that the coupling willhandle without excessive stressing varies with the size ofthe coupling. In all cases, the coupling should be treatedas a joint that will take care of only small misalignments.

2. Installation and Alignment Procedures orCoupling. Figure 50 illustrates the method used tomount each half coupling on the shaft. In reference tofigure 50, place the sleeve over the shaft end andlubricate the surface of the shaft. Expand the hub withheat, using hot oil, steam, or open flame. When using aflame, do not apply the flame to the hub teeth. Use twolong bolts in the puller holes to handle the war coupling.Locate the hub on the shaft with the face of the hubflush with the shaft end. Install the key with a tight fiton the sides and a slight clearance between the top of thekey and the hub.

3. Check the angular alignment, as shown infigures 51 and 52. For normal hub separation, as shownin figure 51, use a feeler gauge at five points 90° apart.Recheck the angular alignment as discussed above.Figure 53 shows how to check the offset alignment bythe sight method. Figure 54 illustrates the method forchecking alignment by the instrument method. Thismethod

54

Figure 51. Checking angular alignment(normal separation).

is recommended by the manufacturer. Fasten or clampthe indicator bracket on one hub with the dial indicatorbutton contacting the alignment surface of the oppositehub. Rotate the shaft on which the indicator is attachedto the hub, and take readings at four point, 90° apart.Move either machine until readings are identical.Reverse the indicator to the opposite hub and check.Recheck the angular alignment as discussed before.

4. Figure 55 illustrates the method for checkingoffset alignment with wide hub separation. Use the dialindicator as discussed in checking offset alignment by theinstrument method, then check the angular alignment asdiscussed before.

5. In checking for angular and offset alignment

Figure 52. Checking angular alignment(wide separation).

Figure 53. Checking offset alignment (sight method).

on the floating shaft arrangement, it is possible to correctboth angular and offset misalignment in one operation.In reference to figure 56, position units to be coupledwith the correct shaft separation. Install and assemblethe coupling. Clamp the indicator bar to the flange ofone coupling with the indicator button resting on thefloating shaft approximately 12 inches from the teethcenterline of this coupling. Rotate the units, takingreadings at four points, 90° apart. Move either machineuntil the readings are identical.

6. After checking and setting the offset and angularalignment, insert the gasket as shown in figure 57.Inspect to insure the gasket is not torn or damaged.Clean the coupling flanges and insert the gasket betweenthe flanges, making sure to position the O-ring in thegroove. Figure 58

Figure 54. Checking offset alignment(instrument method).

55

Figure 55. Checking offset alignment(wide hub separation).

illustrates the method of positioning gaskets between eachset of flanges for spacer and floating shaft type coupling.Assemble the coupling as shown in figure 59. Keep thebolt holes in both flanges and gasket in line. Insert thebody fitting bolts and nuts and tighten the bolts and nutswith wrenches no larger than the one furnished with thecoupling until the flanges are drawn together. Using anoversize wrench on the heads of nuts and bolts mayround their heads or strip the threads.

7. Lubricate the coupling as illustrated in figure 60.Remove both lubricating plugs and apply the quantity andtype of lubricant as specified by the manufacturer'sinstruction data sheet. If grease is used, positioning ofthe lubrication holes is not necessary. When a fluidlubricant is used, it is recommended that the lubricatingholes be positioned approximately 45° from the verticalto prevent loss of lubricant. A good oil lubricant nolighter than 150 seconds Saybolt Universal (SSU)

Figure 56. Checking angular and offset alignment.

Figure 57. Gasket insert.

or heavier than 1000 SSU at 210° F. can be used. Beforereplacing the lubrication plugs, check the copper ringgaskets to make sure they are in position and areundamaged. Tighten plugs with the wrench furnishedwith coupling as shown in figure 61.

8. The coupling must be well lubricated at alltimes. The couplings that use oil collector rings in theend of the cover can be lubricated while stopped orrunning. The compressor should not be started until thecoupling has been checked for proper amount of oil. Oilwill overflow the oiling ring with the coupling at restwhen enough oil has been added. Other types ofcouplings may have sleeves attached by a gasket to thehubs with no oiling ring. The manufacturer will givespecifications as to the amount of oil required to fill thisunit. Unless a large amount of oil is lost from thegasketed type, it is only necessary to check the amount ofoil in the coupling twice a

Figure 58. Insertion of both gaskets.

56

Figure 59. Assembling the coupling.

year by draining and refilling with the correct amount.9. Check of Coupling Alignment on Operating

Machine. In checking the alignment of an operatingcentrifugal unit, proceed as follows: Make sure themachine has operated long enough to bring thecompressor gear and motor up to operating temperatures.Then stop the machine and disconnect both couplings,and with straightedge and feelers check the hubs. Checkthe compressor coupling for parallelism, vertically andhorizontally, noticing how much it will be necessary tomove the gear, vertically or horizontally, to bring thecoupling within 0.002 inch tolerance for alignment. Thencheck the coupling for angularity by use of feelers toinsure that the faces of the hubs are spaced equally apartat the top and bottom. To secure this alignment forangularity, it is necessary to shift the gear at one endeither

Figure 60. Coupling lubrication.

Figure 61. Tightening the coupling plug.

vertically or horizontally. Caution must be used so thatthe parallel alignment is not disturbed. Recheck theparallel alignment to make sure that it is within itstolerance. After the coupling has been aligned, assemblethe coupling. Now that we have reassembled thecoupling, we shall study the drive motor and controls.

13. Drive Motor and Controls1. The motor furnished with a centrifugal machine

is an a.c. electric motor, three-phase, 60 cycle. Themotor will be a general-purpose type with a normalstarting torque, adjustable speed wound rotor and sleevebearings. For wound rotor motors, the controller consistsof three component parts:

• Primary circuit breaker panel• Secondary drum control panel• Secondary resistor grids2. The primary circuit breaker is the main starting

device used to connect the motor to the power supply.Air breakers are supplied for the lower voltages and oilbreakers for 1000 volts. This breaker is a part of thecontrol for the motor and should be preceded by anisolating switch. The breaker provides line protection(short circuit and ground fault) according to the rating ofthe size of breaker and is equipped with thermal over-load relays for motor running protection set at 115percent of motor rating. Undervoltage protection andline ammeter also form a part of the primary panel.

3. The secondary drum control is used to adjustthe amount of resistance in the slipring circuit of themotor and is used to accelerate and regulate the speed ofthe motor. A resistor, which is an energy dissipatingunit, is used with the drum to provide speed regulation.The maximum amount

57

Figure 62. Cross section of the condenser.

of energy turned into heat in the resistor amounts to 15percent of the motor rating. In mounting the resistor,allow for free air circulation by clearance on all sides andat the top.

4. Manual starting of the machine at the motorlocation assures you complete supervision of the unit.Interlocking wiring connections between drum controllerand circuit breaker makes it necessary to return the drumto full low-speed position (all resistance in) before thebreaker can be closed. The oil pressure switch isbypassed when holding the start button closed. Releasingthe start button before the oil pressure switch closes willcause the breaker to trip out-hence a false start. Verylarge size air breakers are electrically operated butmanually controlled by start-stop pushbuttons on thepanel. The drum controller lever must always be movedto the OFF position before pressing the start button.

5. The motor, controlled by various automatic andmanual controls propels the compressor. The compressorin turn pumps the refrigerant through the system'scondenser, cooler, and economizer.

14. Condenser, Cooler, and Economizer1. The condenser is a shell and tube type similar in

construction to the cooler. The primary function of thecondenser is to receive the hot refrigerant gas from thecompressor and condense it to a liquid. A secondaryfunction of the condenser is to collect and concentratenoncondensable gases so that they may be removed bythe purge recovery system. The top portion of thecondenser is baffled, as shown in figure 62. This baffleincloses a portion of the first water pass. Thenoncondensables rise to the top portion of the condenserbecause they are lighter than

58

Figure 63. Condenser diagram.

refrigerant vapors and because it is the coolest portion ofthe condenser.2. A perforated baffle or distribution plate, asshown in figure 62, is installed along the tube bundle toprevent direct impact of the compressor discharge on thetubes. The baffle also serves to distribute the gasthroughout the length of the condenser. The condensedrefrigerant leaves the condenser through a bottomconnection at one end and flows it the condenser floattrap chamber into the economizer chamber. The waterboxes of all condensers are designed for a maximumworking pressure of 200 p.s.i.g. The water box, item 1 infigure 63, is provided with the necessary division plates togive the required flow. Water box covers, items 2 and 3in figure 63, may be removed without disturbing anyrefrigerant joint since the tube sheets are welded into thecondenser and flange. Vent and drain openings areprovided in the water circuit. The condenser isconnected to the compressor and the cooler shell withexpansion joints to allow for differences in expansionbetween them. Figure 63 is a side view of the condenser.3. Condenser. The following procedures should befollowed in cleaning condenser tubes:

(1) Shut off the main line inlet and outlet valves.(2) Drain water from condenser through the water

box drain valve. Open the vent cock in the gauge line orremove the gauge to help draining.

(3) Remove all nuts from the water box covers,leaving two on loosely for safety.

(4) Using special threaded jacking bolts, force thecover away from the flanges. As soon as the covers areloose from the gaskets, secure a rope to the rigging boltin the cover and suspend from overhead. Remove thelast two nuts and place on the floor.

(5) Scrape both the cover and the matching flangefree of any gasket material, items 4, 5, and 6 in figure 63.

(6) Remove the water box division plate by sliding itout from its grooves. Caution should be used inremoving this plate; it is made of cast iron. Penetratingoil may be used to help remove the plate.

(7) Use a nylon brush or equal type on the end of along rod. Clean each tube with a scrubbing motion andflush each tube after the brushing has been completed.CAUTION: Do not permit tubes to be exposed to airlong enough to dry before cleaning since dry sludge ismore difficult to remove.

(8) Replace the division plate after first shellackingthe required round rubber gasket in the two grooves.

(9) Replace the water box covers after first puttinggraphite on both sides of each gasket, since this preventssticking of the gaskets to the flanges. CAUTION: Caremust be taken with the water box cover on the water boxend to see that the division plate matches up the rib tothe flanges.

(10) Tighten all nuts evenly.(11) Close the drain and gauge cock.(12) Open the main line water valve and fill the

tubes with water. Operate the pump, if possible, to checkfor leaktight joints.4. Cooler. The cooler is of horizontal shell and tubeconstruction with fixed tube sheets. The shell is lowcarbon steel plate rolled to shape and electrically welded.The cooler and condenser both have corrosion-resistantcast iron water boxes. They are designed to permitcomplete inspection without breaking the main pipejoints. Full-size separate cover plates give access to alltubes for easy cleaning. The cooler water boxes aredesigned for maximum 200 pounds working pressure.They are provided with cast iron division plates

59

Figure 64. Cross section of cooler.

to give the required water pass flow. Both the cooler andcondenser have tube sheets of cupro-nickel, welded to theshell flange. Cupronickel is highly resistant to corrosion.

5. The tubes in the cooler are copper tubes with anextended surface. The belled ends are rolled intoconcentric grooves in the holes of the tube sheets. Tubeends are rolled into the tube sheets and expanded intointernal support sheets. The normal refrigerant charge inthe cooler covers only about 50 percent of the tubebundle. However, during operation, the violent boiling ofthe refrigerant usually covers the tube bundle. Thecooler is equipped with multibend, nonferrous eliminatorplates above the tube bundle which remove the liquiddroplets from the vapor stream and prevent carryover ofliquid refrigerant particles into the compressor suction.Inspection covers are provided in the ends of the coolerto permit access to the eliminators. Figure 64 is a cross-section diagram of the cooler.

6. A rupture valve with a 15-pound bunting disc isprovided on the cooler, and a 15-p.s.i.g. pop safety valveis screwed into a flange above the rupture disc. Theseitems are strictly for safety, because it is highlyimprobable that a pressure greater than 5 to 8 p.s.i.g. willever be attained without purposely blocking off thecompressor suction opening.

7. An expansion thermometer indicates thetemperature of the refrigerant within the cooler duringoperation. A sight glass is provided to observe thecharging and operating refrigerant level. A charging valvewith connections is located on the side of the cooler foradding or removing refrigerant. The connection is pipedto the bottom of the cooler so that complete drainage ofrefrigerant is possible. A refrigerant drain to theatmosphere is also located near the charging connectionand expansion thermometer.

8. A small chamber is welded to the cooler shell ata point opposite the economizer and above

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the tube bundle. A continuous supply of liquid from thecondenser float chamber is brought to the expansionchamber while the machine is running. The bulb of therefrigerant thermometer and the refrigerant safetythermostat bulb are inserted in this expansion chamberfor measuring refrigerant temperature.

9. Cleaning. Depending on local operatingconditions, the tubes of the evaporator should be cleanedat least once a year. Cleaning schedules should beoutlined in the standard operating procedures. You willbe required to make frequent checks of the chilled watertemperatures in the evaporator. If these temperaturereadings at full load operation begin to vary from thedesigned temperatures, fouling of the tube surfaces isbeginning. Cleaning is required if leaving chilled watertemperature cannot be maintained.

10. Repair. Retubing is about the only major repairthat is done on the evaporator (cooler). This workshould be done by a manufacturer's representative.

11. Cooler and Condenser Checkpoints. You mustcheck the cooler and condenser for proper refrigerantlevel and make sure that the tubes in the cooler andcondenser are in efficient operating condition. Thecorrect refrigerant charging level is indicated by a crosswire on the sight glass. The machine must be shut downto get an accurate reading on the sight glass. Forefficient operation, the refrigerant level must not belower than one-half of an inch below the cross wire; arefrigerant level above this reference line indicates anover-charge. Overcharging is caused by the addition oftoo much refrigerant. When this condition exists, theovercharged refrigerant must be removed.

12. If the machine has been in operation for longperiods of time, the refrigerant level will drop due torefrigerant loss. When this condition exists, additionalrefrigerant must be added to the system to bring therefrigerant level up to its proper height as indicated onthe cross wire. Observe all cautions and do notovercharge the cooler.

13. A method of determining if the tube bundle ofeither the cooler or condenser is operating efficiently is toobserve the relation between the change in temperatureof the condenser water or brine and the refrigeranttemperature. In most cases, the brine or condenserwaterflow is held constant. Under such conditions, thetemperature change of chilled and condenser water is adirect indication of the load. As the load increases, thetemperature difference between the leaving chilled wateror condenser cooling water and the refrigerant increases.A close check should be made of the temperaturedifferences at full load when the machine is firstoperated, and a comparison made from time to time

during operation. During constant operation over longperiods of time, the cooler and condenser tubes maybecome dirty or scaled and the temperature differencebetween leaving water or brine will increase. If theincrease in temperature is approximately 2° or 3° at fullload, the tubes should be cleaned.

14. Read the condenser pressure gauge when takingreadings of the temperature difference between leavingcondenser water and condensing temperature. Beforetaking readings, make sure the condenser is completelyfree of air. The purge unit should be operated for atleast 24 hours before readings are taken.

15. Economizer. A complete explanation of thefunction of the economizer was given under therefrigeration cycle. The economizer is located in thecooler shell at the opposite end from the compressorsuction connection and above the tube bundle.

16. The economizer is a chamber with the necessarypassages and float valves, connected by an internalconduit passing longitudinally through the cooler gasspace to the compressor second-stage inlet. Thisconnection maintains a pressure in the economizerchamber that is intermediate (about 0 p.s.i.g.) betweenthe cooler and condenser pressures and carries away thevapors generated in the chamber. Before entering theconduit, the economizer vapors pass through eliminatorbaffles to extract any free liquid refrigerant and drain itback into the chamber. (Item 9 of fig. 64 is a front viewof the economizer chamber.)

17. There are two floats in separate chambers on thefront end of the economizer. The top or condenser floatvalve keeps the condenser drained of refrigerant andadmits the refrigerant from the condenser into theeconomizer chamber. The bottom, or economizer, floatvalve returns the liquid to the cooler.

18. This system is also equipped with another finefeature to assure smoother operation. Let's discuss thehot gas bypass system.

15. Hot Gas Bypass1. The automatic hot gas bypass is used to prevent

the compressor from surging at low loads. In case of lowload conditions, hot gas is bypassed directly from thecondenser through the cooler to the suction side of thecompressor. The hot gas supplements the small volumeof gas that is being evaporated in the evaporator due tolow load conditions. Surging generally occurs at lightload, and the actual surge point will vary with differentcompressors. In most instances, it usually develops atsome point well below 50 percent capacity. If the leavingchilled water is held at a constant

61

Figure 65. Hot gas bypass.

temperature, the returning chilled water temperaturebecomes an indication of the load. This temperature isused to control the hot gas bypass. A thermostat, set inthe returning chilled water, operates to bleed air off thebranch line serving the hot gas bypass valve. Thethermostat is set to start opening the bypass valve slightlybefore the compressor hits its surge point. Figure 65illustrates components and location of the hot gas bypassline.

2. A liquid line injection system is provided in thehot gas bypass system to desuperheat the gas byvaporization in the bypass line before it enters thecompressor suction. If the gas is not desuperheated, thecompressor will overheat. The automatic liquid injectionsystem components consist of a pair of flanges in the hotgas line, an orifice, a liquid line from the condenser toone of the flanges, and a liquid line strainer with twoshutoff valves.

3. The automatic valve shown in figure 65 isnormally closed. When this valve is closed, there is noflow of gas through the orifice. The pressure at point M,just below the orifice, is the same as the condenserpressure; therefore, no liquid will flow through the liquidline. When the occasion arises for the need of hot gas,the valve is opened automatically and a pressure drop willexist across the orifice. The amount of pressure drop is adirect function in determining the rate of gasflowthrough the orifice. The larger the flow of hot gasthrough the bypass and orifice, the lower the pressure atpoint M will become in relation to the condenserpressure, and the greater will be the pressure differentialto force desuperheating liquid through the liquid line. Asthe amount of hot bypass gas is increased or decreased by

the opening or closing of the valve, the amount ofdesuperheating liquid forced through the liquid line isautomatically increased or decreased.

4. The two shutoff valves in the liquid line arenormally left wide open and are closed only to service theliquid line components. The special flange (located nearthe orifice) is installed at a slightly higher level than thesurface of the liquid lying in the bottom of thecondenser. When no hot gas is flowing through thebypass, no unbalance will exist in the liquid line.Therefore, the liquid will not flow and collect in the gaspipe above the automatic valve. This prevents the dangerof getting a “slug” of liquid through the hot gas bypassline whenever the valve is opened. It also provides ameans of distributing the liquid into the hot gas stream asevenly and as finely as possible. The flange isconstructed with a deep concentric groove in one face foreven distribution of the liquid.

5. How are undesirables such as water and airexpelled from this system? The purge unit will do thisimportant task for us.

16. Purge Unit1. The presence of even a small amount of water

in a refrigeration system must be avoided at all times;otherwise excessive corrosion of various parts of thesystem may occur. Any appreciable amount of water iscaused by a leak from one of the water circuits. Sincethe pressure within a portion of the centrifugalrefrigeration system is less than atmospheric, thepossibility exists that air may enter the system. Since aircontains water vapor; a small amount of water will enterwhenever air enters.

2. The function of the purge system is to removewater vapor and air from the refrigeration system and torecover refrigerant vapors which are mixed with thesegases. The air is automatically purged to the atmosphere.The refrigerant is condensed and automatically returnedto the cooler as a liquid. Water, if present, is trapped in acompartment of the purge separator unit from which itcan be drained manually. Thus the purge and recoverysystem maintains the highest possible refrigeratingefficiency.

3. Components. The following discussion of thecomponent items of the purge system is referenced tofigure 66.

• Stop valve--on main condenser, item 1. Thisvalve is always open except during repairs.

• Pressure-reducing valve--in suction line, item 2,to regulate the compressor suction pressure.

• Stop valve--in suction line, item 3, located in theend of the purge unit casing. This valve is to be openwhen the purge unit is in operation and closed at allother times.

• Pressure gauge--this gauge, item 4, indicates

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Figure 66. Purge unit schematic.

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the pressure on the oil reservoir. NOTE: Before addingoil, at item 23, be sure the pressure is at zero.

• Compressor, item 5--to be operated continuouslywhen the centrifugal compressor is operating, and beforestarting the machine as required by the presence of air.

• High-pressure cutout switch, item 7--connectedto the compressor discharge. Adjusted to stop thecompressor if the purge condenser pressure increases toabout 110 p.s.i.g. because of some abnormal condition.The switch closes again automatically on the reduction ofpressure to about 75 p.s.i.g.

• Auxiliary oil reservoir, item 8--this reservoirserves as a chamber to relieve the refrigerant from thecompressor crankcase and also to contain extra oil for thecompressor. The refrigerant vapor, which flashes fromthe compressor crankcase, passes up through the reservoirand into the compressor suction line. The free spaceabove the oil level separates the oil from the refrigerantvapor before the vapor goes into the suction side of thepurge compressor. The oil storage capacity of thereservoir is slightly larger than the operating charge of oilrequired by the compressor.

• Sight glass, item 9--for oil level in thecompressor and auxiliary oil reservoir, located in front ofcasing.

• Compressor discharge line, item 10.• Condenser, item 11--cooled by air from a fan on

compressor motor. It liquefies most of the refrigerantand water vapor contained in the mixture delivered bythe compressor.

• Evacuator chamber, item 12--for separation ofair, refrigerant, and water. Chamber can be easily takenapart for inspection and repairs.

• Baffle, item 13--allows the condensate to settleand air to separate for purging. This is the delivery pointfor the mixture of air, water (if any), and liquidrefrigerant from condenser.

• Weir and trap, item 14--located in the center ofevacuation chamber. Since the water is lighter thanliquid refrigerant the water is trapped above the liquidrefrigerant in the upper compartment. Only refrigerantliquid can pass to the lower compartment.

• Float valve, item 15--a high-pressure float valve,opening when the liquid level rises, allows the gaspressure to force the liquid refrigerant into theeconomizer.

• Equalizer tube, item 16--to equalize the vaporpressure between the upper and lower compartments.

• Two sight glasses, items 17 and 17A--on lowerliquid compartment, visible at the end of the casing.These glasses show refrigerant level in the separator.

• Sight glass, item 18--on upper compartment toindicate the presence of water.

• Stop valve at the end of casing, item 19--permitswater to be drained from the upper compartment. Thevalve is marked "Water Drain" and is closed except whendraining water.

• Automatic relief valve, item 20--to purge air tothe atmosphere.

• Stop valve marked “Refrigerant Return" in thereturn liquid refrigerant line, item 21-located at the endof the casing. Open only when purge is operating.

• Stop valve, item 22--on economizer in the returnrefrigerant connection. Open at all times except whenmachine is shut down for a long period or being tested.

• Plug in oil filling connection of reservoir, item23--pressure in the system must be balanced with theatmospheric pressure to add oil through this fitting.

• Cap, item 24--or draining oil from thecompressor crankcase and oil reservoir. Oil may also beadded through this connection (not shown in fig. 66) if(1) a packless refrigerant valve is installed in place of capat the connection and (2) the purge compressor isoperated in a vacuum.

• Connections between auxiliary reservoir andcompressor crankcase, item 25.

• Motor and belt--not shown in figure 66.• Wiring diagram inside the casing.• Casing that completely incloses the purge

recovery unit and is removable to provide a means towork on components.

• Plugged tee after pressure-reducing valve on linefrom condenser, item 26.

• Capped tee on line leading to cooler, item 27.• Temporary connector pipe from water drain

from separator to liquid refrigerant line to cooler, item28.

4. Purge Recovery Operation. The purge recoveryoperation is automatic once the purge switch is turned onand the four valves listed below and referred to in figure66 are opened:

(1) Stop valve on main condenser(2) Stop valve in suction line(3) Stop valve in the return liquid refrigerant line(4) Stop valve on economizer in return refrigerant

connection5. If there should be an air leakage in the system,

operation of the purge unit will remove this air. It isrecommended that you stop the purge unit at intervalsand shut off valves (1) an (4) listed above to check forleaks in the system. A tight machine will not collect airno matter how long the purge unit is shut off. Presenceof air in the system is shown by an increase in head

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Figure 67. Suction and relief pressure.

pressure in the condenser. The pressure can developsuddenly or gradually during machine operation. Bychecking the difference between leaving condenser watertemperature and the temperature on the condenser gauge,you can determine the presence of air. A suddenincrease between these temperatures may be caused byair. In some instances, a sudden increase in coolerpressure over the pressure corresponding to coolertemperatures during operation may be caused by airleakage.

6. Small air leakages are very difficult to determine.It may take one or more days to detect an air leakage inthe machine. A leak that shows up immediately orwithin a few hours is large and must be found andrepaired immediately. Air pressure built up in thecondenser is released to the atmosphere by the purge airrelief valve. Excessive air leakage into the machine willcause the relief valve to pop off continuously, resulting ina large amount of refrigerant discharged to theatmosphere.

7. Refrigerant loss depends on operationalconditions; therefore, these conditions have adetermining effect on the amount of refrigerant lost.You should maintain a careful log on refrigerant chargedand the shutdown level in the cooler. In this manner,you can determine the time a leak develops and theamount of refrigerant lost, find the cause, and correct thetrouble.

8. Moisture removal by the purge recovery unit isjust as important as air removal. The moisture may enterthe machine by humidity in the air that can leak into themachine or by a brine or water leak in the cooler orcondenser. If there are no water leaks, the amount ofwater collected by the purge unit will be small (1 ounceper day) under normal operating conditions. If largeamounts of water are collected by the purge unit (one-half pint per day), the machine must be checked for leakytubes. Water can be removed more rapidly when themachine is stopped than when operating. If the machine

is collecting a large amount of moisture. It is advisableto run the purge unit a short time after the machine isstopped and before it is started. Running the purge unitbefore the machine is started will help to reduce purgingtime after the machine is started.

9. The pressure-reducing valve (2), shown in figure66, is adjusted to produce a suction pressure on the purgerecovery unit and will not allow condensation in thesuction line. If condensation does occur, the condensatewill collect in the crankcase of the purge unit compressor,causing a foaming and excessive oil loss. The table infigure 67 can be used as a guide for setting the pressure-reducing valve. If the pressure-reducing valve is wideopen, there will be a pressure drop of a few poundsacross the valve and the suction pressure cannot beadjusted higher than a few pounds below the machinecondensing pressure.

10. Purge Unit Maintenance. After repairs orbefore charging, it is necessary to remove large quantitiesof air from the machine. This can be done bydischarging the air from the water removal valve (item19, fig. 66). Caution must be observed in the removal ofair, since there is some danger of refrigerant beingdischarged with the air and being wasted to atmosphere.

11. If the normal delivery of refrigerant isinterrupted, it is usually caused by the stop valve (item 21,fig. 66) being closed or because the float valve is notoperating. This malfunction is indicated by a liquid risein the upper sight glass. Immediate action must be takento correct this trouble. If the liquid is not visible in thelower glass, the float valve is failing to close properly.

12. Water or moisture in the system will collect onthe top of the refrigerant in the evacuation chamber. Ifany water does collect, it can be seen through the uppersight glass and should be drained. In most normaloperating machines, the water collection is small; but if alarge amount of water collects quite regularly, a leak inthe condenser or cooler has most likely occurred andmust be located and corrected immediately.

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Figure 68. Control panel electrical diagram.

13. The purge unit compressor and centrifugalcompressor use the same type and grade of oil. Oil canbe added to purge the compressor by closing stop valves(items 3 and 21, fig. 66), removing plug (23) in the top ofthe oil sight glass, and adding oil. Oil can be drained byremoving the oil plug (24, fig. 66). The oil level can bechecked by a showing of oil at any point in the oil sightglass while the compressor is running or shut down. Thelevel of oil will fluctuate accordingly. The oil levelshould be checked daily.

14. Other components that must be closely checkedin the purge recovery unit are as follows:

• Belt tension.• Relief valve for rightness when closed to prevent

loss of refrigerant.• Condenser clean and free from air obstruction• High-pressure cutout which shuts down if

condenser pressure reaches 110 pounds.15. CAUTION: The high-pressure cutout remakes

contact automatically to startoff the purge recovery uniton 75 pounds. Single-phase motors have a built-inthermal overload to stop the motor on overload. Itautomatically resets itself to start the motor in a fewminutes.

16. The system is running and purged. Let us nowstudy our safety controls:

17. Safety Controls1. Safety controls are provided to stop the

centrifugal machine under any hazardous condition.Figure 68 illustrates the electrical wiring diagram. All thecontrols are mounted on a control panel. The safetycontrols are as follows:

• Low water temperature cutout• High condenser pressure cutout• Low refrigerant temperature cutout• Low oil pressure cutout2. All of the safety controls except the low oil

pressure cutout are manual reset instruments. Eachsafety instrument operates a relay switch which has onenormally open and one normally closed contactor. Whena safety instrument is in the safe position, thecorresponding relay is energized and the current is passedthrough the closed contactor to a pilot light which lightsto indicate a safe operating condition. Should an unsafecondition exist, a safety control will deenergize thecorresponding relay and the normally open contactor willopen to deenergize the pilot light; the normally closedcontactor will then close to energize the circuit breakertrip circuit.

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When the circuit breaker trip circuit is energized, thecircuit breaker trips open and stops the compressormotor. The pilot light will not go back on until a safeoperating condition exists and the safety cutout has beenmanually reset. The oil safety switch operates somewhatdifferently. Since the oil pressure is not up to designconditions until the compressor comes up to speed, therelay for the oil pressure switch must be bypassed whenthe machine is started. The relay for the oil safety switchis bypassed by a time-delay relay, which keeps the tripcircuit open until the compressor is up to speed. After apredetermined time interval, the time-delay relay closesthe trip circuit at the circuit breaker and the oil safetyswitch serves its function. If the oil pressure does notbuild up before the time-delay relay closes, the trip circuitwill be energized and the machine will stop.

3. The low oil pressure cuts out at 6 pounds and inat 12 pounds. The high condenser pressure cuts out at 15pounds and in at 8 pounds. The low refrigerant andtemperature cutout is set after operation in accordance tothe job requirement. Generally, these controls should beset to cut out at 32° F. and to cut in at approximately 35°F. The low water temperature cutout should be set tocut out at 38° F. and to cut in at 43° F.

4. There are other safety controls built into thecircuit breaker which are not part of the control panel,and reference should be made to the circuit breakeroperating instructions for details of these controls. Suchitems as overload protection and undervoltage protectionwill be covered therein.

5. In addition to the pilot lights mentioned, a pilotlight for the purge high-pressure cutout is on the safetycontrol panel. The high-pressure cutout, which serves toprotect the purge recovery compressor from high headpressure, is located in the purge recovery unit. When thehigh-pressure cutout functions on high head pressure, thepilot light on the control panel is lighted.

6. One or more machines at each installation areprovided with two sets of starting equipment. One set isan operating controller and the other a standby controller.In order that the machine safety controls can operate thecontrolling breaker, a rotary selector switch is provided onthe safety control panel. By means of the rotary selectorswitch, the machine safety controls can operate either ofthe controlling circuit breakers. Safety controls are usedfor safe operation of the system, but operating controlsaffect the capacity.

18. Operating Controls1. The three methods of controlling the capacity

output of a centrifugal machine are listed below:• Controlling the speed of the compressor• Throttling the suction of the compressor• Increasing the discharge pressure of the

compressor.2. The three methods given are listed in order of

their efficiency. At partial loads, the power requirementswill be least if the compressor speed is reduced, not quiteas low if the suction is throttled, and highest if thecondenser water is throttled to increase the dischargepressure.

3. Where the compressor is driven by a variable-speed motor, motor speed and compressor speed arecontrolled by varying the resistance in the rotor circuit ofthe motor by means of a secondary controller.

4. Damper Control. Throttling the suction of thecompressor is obtained by means of a throttling damperbuilt into the cooler suction flange. By throttling thecompressor suction, the pressure differential throughwhich the compressor must handle the refrigerant vaporis increased. Suction damper control requires somewhatmore power at partial loads than at variable-speed control.The increase in power consumption is overbalanced bythe increased effectiveness in maintaining a nonsurgingoperation at lower loads. For this reason, the machinesare equipped with dampers, even though the main controlis variable speed. Suction damper control modulation iseffected by means of a temperature controller that sendsair pressure signals to the suction damper motor inresponse to temperature changes of chilled water leavingthe cooler.

5. Condenser Water Control. By throttling thecondenser water, the condenser pressure is increased,thereby increasing the pressure differential on thecompressor and reducing its capacity. The occasion mayarise where the variable-speed control cannot be adjustedlow enough to meet operating conditions. In such a case,the condenser water may be throttled and the compressorspeed requirement brought up into the range of speedcontrol.

6. Speed control and suction damper control arecombined to control the temperature of the chilled waterleaving the cooler. The suction damper modulates tocontrol the leaving chilled water temperature on eachbalanced speed step. As the refrigeration load decreases,the suction damper will gradually close in response todecreasing air pressure in the branch line from thesuction damper controller. As the suction damperapproaches the closed position, a light on the

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control panel will indicate that the motor speed should bedecreased to the next balanced step. The converse is trueif the refrigeration load increases.

7. The lights for indicating a speed change areenergized by mercury type pressure controls that sensebranch air pressure from the suction chamber controller.The controller that energizes the "speed decrease" lightalso closes the light circuit on decreasing branch airpressure; the controller that energizes the "speedincrease" light also closes the light circuit on increasingbranch air pressure. The control system drawings giveactual settings for pressure controllers; the final settingsshould be determined under actual operating conditions.You must determine what pressure change corresponds toa speed change and then adjust the pressure controlleraccordingly. Refer to the manufacturer's manual ondetails of adjustments. This information on operatingcontrols will help you better understand the operation ofthe entire system.

19. System Operation1. It is very difficult to give definite instructions in

this text on the operating procedures for a giveninstallation. Various design factors change the location ofcontrols, types of controls used, and equipment location,and will have a definite effect on operational procedures.Listed below is a general description of startup andshutdown instruction. It is recommended that you followyour installation standard operating procedures fordefinite operating instructions.

2. Seasonal Starting. Listed below are therecommended steps that can be used in normal starting:

(1) Check oil levels for motor, gear, coupling,compressor, and bearing wells.

(2) Allow condenser water to circulate through thecondenser. Be sure to vent air and allow the water toflow through slowly. This precaution must be observedto avoid water hammer.

(3) Allow water or brine to circulate through thecooler. Be sure to vent air and allow the liquid to flowthrough slowly. As explained above, this will help inpreventing water hammer.

(4) Make sure that air pressure is present at all air-operated controls.

(5) Start the purge unit before starting the machine;this helps in removing air from the machine. Thenmove the switch on the front of the casing to the ONposition. The purge recovery unit should be operated atall times while the machine is operating.

(6) Make sure all safety controls have been resetand that the control lever is in position No. 1 (allresistance in).

(7) Close the circuit breaker for all safety controlsby pushing the starting switch or button in.

(8) Bring the machine up to 75 percent full loadwith all resistance in. Check oil gauges to make sureproper oil pressure is being developed. If proper oilpressure is not developed in approximately 10 seconds,the machine will cut out on low oil pressure.

(9) Open the valve to allow the cooling water tocirculate to the compressor oil cooler, gear or turbine oilcooler, and seal jacket. The water circulating to thecompressor oil cooler must be kept low enough intemperature to prevent the highest bearing temperaturefrom exceeding a temperature of 130° F. Then adjust togive a temperature from 140° F. to 180° F. The sealbearing temperature should run approximately 160° F.,while the thrust bearing temperature is running atapproximately 145° F. under normal operating conditions.These temperatures should be checked closely until theymaintain a satisfactory point.

(10) After starting, the machine may surge until theair in the condenser has been removed. During thissurging period, the machine should be run at a highspeed; this helps in the process of purging. Thecondenser pressure should not exceed 15 p.s.i.g., and theinput current to motor-driven machines should not runover 100 percent of the full load motor rating. Themachine will steady itself out as soon as all the air hasbeen purged. After leveling out the motor speed, thedamper maybe adjusted to give the desired coolanttemperature. The motor should be increased slowly,point to point. Do not proceed to the next speed pointuntil the motor has obtained a steady speed. Keep aclose observation on the ammeter to make sure that themotor does not become overloaded.

3. Normal and Emergency Shutdown. Normalshutdown procedures are performed in the same manneras emergency shutdown procedures. The following stepsare used in shutting down the centrifugal machine:

(1) Stop the motor by throwing the switch on thecontroller.

(2) After the machine has stopped, turn off thewater valve which supplies water to the compressor oil,gear oil cooler, and seal housing.

(3) Shut down all pumps as required.4. Shutdown periods may be broken down into two

classes. The two classes are standby and extendedshutdown. Standby shutdown may be machine must beavailable for immediate use;

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extended shutdown is defined as that period of timeduring which the machine is out of service.

5. Standby shutdown. The following checks mustbe made during standby shutdown and corrective actiontaken:

(1) Maintain proper oil level in the oil reservoir andin the suction damper stuffing box.

(2) Room temperature must be above freezing.(3) Machine must be kept free of leaks.(4) Purge unit must be operated as necessary to keep

the machine pressure below atmospheric pressure.(5) If the machine pressure builds up in the unit due

to room temperature rather than leakage of air into themachine, a small quantity of water circulated through thecondenser or cooler will hold the machine pressure belowatmospheric. Periodic operation of the purge unit willaccomplish the same result.

(6) The machine should be operated a few minuteseach week to circulate oil and lower the refrigeranttemperature.

6. Extended shutdown. If the system is free of leaksand the purge unit holds down the machine pressure, thefollowing instructions and corrective actions must betaken in long shutdown periods:

(1) Drain all water from the compressor, gear andturbine oil cooler, condenser, cooler, seal jacket, pumps,and piping if freezing temperatures are likely to developin the machine room.

(2) It is possible for the oil to become excessivelydiluted with refrigerant, causing the oil level in the pumpchamber to rise. This level should not be allowed to riseinto the rear bearing chamber; if this occurs, remove theentire charge of oil.

7. Logs and Records. A daily operating log ismaintained at each attended plant for a record ofobserved temperature readings, waterflow, maintenanceperformed, and any unusual conditions which affect aninstallation operation. You are held responsible forkeeping an accurate log while on duty. A good log willhelp you spot trouble fast. A typical log sheet has spacesfor all important entries, and a carefully kept log will helpto make troubleshooting easier.

8. A master chart of preventive maintenanceduties, each component identified, is usually prepared bythe supervisor and includes daily, weekly, and monthlymaintenance services. The preventive maintenance itemsincluded on the chart are applicable to a specificinstallation. The items on the chart must be checkedaccordingly. Proper sustained operation is the result ofgood maintenance.

20. Systems Maintenance1. It is very difficult to set up a definite

maintenance schedule since so many operational factorsmust be considered. You must familiarize yourself withthe operating procedures at your installation and followrecommendations. We shall discuss the properprocedures for replacing oil, charging the unit, removingrefrigerant, and troubleshooting.

2. Replacing Oil. The following procedure is usedin the renewal of the oil:

(1) Pressure in the machine should be approximately1 p.s.i.g.

(2) Drain oil from the bottom of the main oilreservoir cover.

(3) Remove the main oil reservoir cover and cleanthe chamber to remove all impurities.

(4) Replace the main oil reservoir cover and securetightly.

(5) Remove the bearing access cover plates.(6) Lift up the shaft bearing caps by reaching

through the bearing access hole and removing the twolarge capscrews.

(7) Fill the bearing approximately three-fourths ofthe full charge, allowing the excess oil to flow into themain oil reservoir.

(8) Replace the bearing cap and secure withcapscrews.

(9) Remove the brass plug from the thrust housing,and remove the strainer; clean and replace.

(10) Replace the plug and secure.(11) Drain oil through the plug in back of the seal oil

reservoir.(12) Remove the cover from the seal oil reservoir.(13) Remove the filter from the chamber; replace

with a new filter.(14) Refill the reservoir with oil.(15) Replace the cover and secure tightly.(16) Drain the oil through the plug at the bottom of

the atmospheric oil reservoir.(17) Remove the atmospheric oil filling plug and pour

in fresh oil until the level is halfway in the atmosphericreservoir sight glass.

(18) Replace the plug and secure tightly.(19) Operate the purge unit to remove as much air as

possible.(20) Add oil to the atmospheric float chamber, if

main oil reservoir indicates under-charge after shortoperation.

3. Charging the Unit. The manufacturer ships therefrigerant (R-11) in large metal drums which weighapproximately 200 pounds. At temperatures above 74°F., the drum will be under pressure. To prevent injury orloss of refrigerant, never open the drums to theatmosphere when they are above this temperature.

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It is possible to charge refrigerant from an open drum a60° temperatures, although it is recommended thatleaktight connections be made to the charging valve. Thecharging valve is located on the side of the cooler. Tohelp in the charging procedure, each refrigerant drum hasa special type plug installed on the side of the drum.This plug is specially engineered for charging purposes.The charging connection on the drum consists of a 2-inch plug in which is inserted a smaller 3/4-inch plug.The 3/4-inch opening inside the drum is covered with afriction cap. The cap prevents leakage into or out of thedrum when the 3/4-inch plug is unscrewed.

4. Refrigerant charging. To charge the machinewith refrigerant, proceed as follows:

(1) The machine must be under a vacuum.(2) Fit a 3/4-inch nipple into the standard globe

valve and close the valve.(3) Remove the 3/4-inch plug inserted in the 2-inch

plug from the drum.(4) Place the valve with the nipple into the opening,

making sure that it is far enough in to push off the capinside the drum.

(5) Place the drum in a horizontal position near thecooler charging valve with the use of a hoist. The drumshould be high enough to allow the refrigerant to flow asa liquid, by gravity, from the drum into the charging line.Rotate the drum so that the valve is at the bottom.

(6) Connect the two valves (drum and cooler) witha copper tube and fittings, making sure all the joints areleakproof.

(7) Open both valves and allow the refrigerant toflow into the cooler. Operate the machine to maintain avacuum after the initial reduction to zero.

(8) When the drum is empty, close the valve on thecooler and disconnect the drum. Remove the valve foruse with the next drum. Complete charging of themachine requires 1200 pounds of refrigerant.

5. Adding refrigerant to bring refrigerant to standardlevel. When adding refrigerant, use the same proceduresthat we have just discussed. Another method that can beused to add refrigerant is simply to allow the refrigerantto be drawn in as a gas. Let the drum rest on the floorand let the gas escape into the cooler while the machineis in operation or idle.

6. Removing refrigerant. In removing refrigerantfrom the cooler, the following procedure isrecommended:

(1) By use of the purge recovery unit, inject air intothe machine until the pressure is 5 pounds gauge.

(2) Connect tubing to the charging valve on thecooler and allow the refrigerant to discharge into therefrigerant drum.

(3) Less loss of refrigerant will take place if therefrigerant is cold. Always allow space in the drum forrefrigerant expansion.

7. Troubleshooting. The steps to be taken indetecting and correcting improper operation of thecentrifugal machine are outlined in table 19. Use theproper methods for making these service adjustments,repairs, and corrections as outlined in this chapter. Allsettings, clearances, and adjustments must be made tomanufacture’s specifications. The manufacturer’smaintenance catalog gives definite clearances,temperatures, pressure, and positions for adjustment ofcomponent parts. These tolerances must be set asrecommended for efficient operation; carelessness inthese settings can cause extensive damage to themachine.

TABLE 19

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TABLE 19-continued

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TABLE 19-Continued

Review Exercises

The following exercises are study aids. Write youranswer in pencil in the space provided after each exercise. Usethe blank pages to record other notes on the chapter content.Immediately check your answers with the key at the end of thetext.

1. The refrigerant charge is approximately___________ pounds. (Sec. 9, Par. 1)

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2. Which component reduces the horsepowerrequirement per ton of refrigeration? (Sec. 9,Par. 2)

3. (Agree)(Disagree) The refrigerant flows throughthe tubes in the cooler. (Sec. 9, Par. 3)

4. The liquid refrigerant, from the condenser,enters the _______________. (Sec. 9, Par.5)

5. How much pressure is there within theeconomizer chamber? (Sec. 9, Par. 5)

6. The suction gas is taken in by the compressor in_____________ the shaft. (Sec. 10, Par. 1)

7. How are the wheels (impellers) protected fromcorrosion? (Sec. 1, Par. 2)

8. Each bearing has ______________ large oilrings. (Sec. 10, Par. 3)

9. What prevents interstage leakage of gas? (Sec.10, Par. 4)

10. Which end of the compressor will axial thrustaffect? (Sec. 10, Par. 5)

11. The oil pump is driven from the_____________________. (Sec. 10, Par. 7)

12. Which component does the pump lubricate first?(Sec. 10, Par. 8)

13. How is oil returned from the oil pump drivegear? (Sec. 10, Par. 9)

14. How is the shaft seal actuated? (Sec. 1, Par. 10)

15. What purpose do the two holes in the innerfloating seal ring serve? (Sec. 10, Par. 11)

16. The automatic stop valve is set to open atapproximately ________________ pounds.(Sec. 10, Par. 12)

17. Which oil pressure gauges are mounted on thecontrol panel? (Sec. 10, Par. 13)

18. How is the oil heater energized duringshutdown? (Sec. 10; Par. 14)

19. (Agree)(Disagree) During operation the twopolished surfaces of the shaft seal are heldtogether with a spring. (Sec. 10, Par. 16)

20. What type oil is used in centrifugal compressors?(Sec. 10, Par. 17)

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21. The compressor gear drive (increases, decreases)the motor to compressor speed. (Sec. 11, Par. 1)

22. The grade of oil to use on a gear depends on__________, ___________, and______________.(Sec. 11, Par. 3)

23. When would you turn on the gear drive coolingwater? (Sec. 11, Par. 5)

24. Worn bearings in the gear drive will cause___________________. (Sec. 11, Par. 9)

25. Which coupling uses a spool piece? (Sec. 12,Par. 1)

26. How is the hub expanded when it is to beinstalled on the shaft? (Sec. 12, Par. 2)

27. The angular alignment of a coupling is checkedwith a _________________. (Sec. 12, Par. 3)

28. Which instrument is used to check the offsetalignment of a coupling? (Sec. 12, Par. 4)

29. Which type of coupling can be lubricated whilethe compressor is running? (Sec. 12, Par. 8)

30. The motor furnished with the centrifugalmachine is __________ phase,_________________ cycle, and has an________________ rotor. (Sec. 13, Par. 1)

31. The secondary drum control is used to adjustthe amount of resistance in the___________________ of the motor whichregulates motor ____________________(Sec. 13, Par. 3)

32. Which switch is bypassed when the start buttonis held closed? (Sec. 13, Par. 4)

33. What is the secondary function of thecondenser? (Sec. 14, Par. 1)

34. What prevents the discharge gas from directlyhitting the condenser tubes? (Sec. 14, Par. 2)

35. What precaution would you observe whileremoving the water box cover? (Sec. 14, Par. 3)

36. A burst rupture disc is caused by__________________ (Sec. 14, Par. 6)

37. How can you determine the refrigerant chargeof the system? (Sec. 14, Par. 11)

38. What is indicated when the temperaturedifferential of the refrigerant and chilled waterincreases? (Sec. 14, Par. 13)

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39. ________________ is prevented by the hotgas bypass. (Sec. 15, Par. 1)

40. Why is the liquid injector used in the hot gasbypass? (Sec. 15, Par. 2)

41. What controls the amount of liquid refrigerantflowing to the hot gas bypass? (Sec. 15, Par. 3)

42. (Agree) (Disagree) The high-pressure control onthe purge unit must be reset manually. (Sec. 16,Par. 3)

43. Where is the weir and trap located on the purgeunit? (Sec. 16, Par. 3)

44. High head pressure indicates that___________________. (Sec. 16, Par. 5)

45. How is the air pressure in the condenserreleased to the atmosphere? (Sec. 16, Par. 6)

46. What amount of water collected by the purgeunit is an indication of leaky tubes? (Sec. 16,Par. 8)

47. When will a pressure drop exist across thepressure-regulating valve? (Sec. 16, Par. 9)

48. When are large quantities of air normally purgedfrom the centrifugal refrigeration system? (Sec.16, Par. 10)

49. When is water drained from the separator unit?(Sec. 16, Par. 12)

50. The four safety controls that will stop thecentrifugal are _______________,________, ___________, and_______________. (Sec. 17, Par. 1)

51. Which safety control does not require manualresetting? (Sec. 17, Par. 2)

52. What is the differential for the high condenserpressure control? (Sec. 17, Par. 3)

53. How can you change (switch over) controllers?(Sec. 17, Par. 6)

54. The most efficient method of controlling thecapacity of the centrifugal is to____________________. (Sec. 18, Pars. 1and 2)

55. What will occur if you add more resistance tothe rotor circuit of the drive motor? (Sec. 18,Par. 3)

56. When is suction damper control more effectivethan speed control? (Sec. 18, Par. 4)

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57. What is the position of the drum controller leverduring startup? (Sec. 19, Par. 2)

58. What will cause the oil level to rise in the pumpchamber during an extended shutdown? (Sec.19, Par. 6)

59. The pressure within the machine during an oilreplacement operation should be approximately_______________ p.s.i.g. (Sec. 20, Par. 2)

60. (Agree)(Disagree) The 2-inch plug in therefrigerant drum prevents leakage when the 3/4-inch plug is removed. (Sec. 20, Par. 3)

61. How is refrigerant charged into the system as agas? (Sec. 20, Par. 5)

62. How do you pressurize the system to removerefrigerant? (Sec. 20, Par. 6)

63. What is one of the most probable causes of highcondenser pressure? (Sec. 20, table 19)

64. Surging is caused by _________________,________________, or________________. (Sec. 20, table 19)

65. What would occur if the economizer float valvestuck? (Sec. 20, table 19)

66. What will cause a low "back of seal" oil pressureand a high seal oil pressure? (Sec. 20, table 19)

67. Noisy couplings are caused by___________________,________________, or_________________. (Sec. 20, table 19)

68. (Agree)(Disagree) A high oil level in the speedgear will cause the gear to overheat. (Sec. 20,table 19)

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CHAPTER 4

Water Treatment

WATER USED IN air-conditioning systems may createproblems with equipment, such as scale, corrosion, andorganic growths. Scale formation is one of the greatestproblems in air-conditioning systems that have water-cooled condensers and cooling towers. Corrosion isalways a problem in an open water recirculating system inwhich water sprays come in contact with air. Theorganic growth we are greatly concerned with is algae orslime. Since algae thrive on heat and sunlight they willbe a problem in cooling towers. As a refrigerationspecialist or technician you will save the military greatsums of money if you test and treat your equipmentwater. For example, if you allowed scale to reach thethickness of a dime in a water-cooled condenser, it wouldcut the efficiency of the machine more than 50 percent.

21. Scale

1. When water is heated or evaporated, insolublesare deposited on metal surfaces. These deposits usuallyoccur on the metal in the cooling towers, evaporativecondensers, or inside the pipes and tubes of thecondenser water system which have a recirculating watersystem. What causes scale? We can explain it in asimple formula:

Ca (HCO3) + heat = CaCO3, + CO2 + H2O Calcium calcium carbon

bicarbonate + heat = carbonate + dioxide + water

In this formula the calcium carbonate is the villain.Calcium carbonate is the chief scale-forming deposit foundin air-conditioning systems, but magnesium carbonate andcalcium sulfate can also cause some degree of scaling.

2. Causes of Scale. A rising temperaturedecreases the solubility of calcium carbonate and calciumsulfate. This is known as reverse solubility. Sodiumcompounds such as table salt (sodium chloride), on theother hand, have a direct solubility. Suppose you take aglass of water 80° F. and dissolve table salt into thewater. Soon

you will saturate the water and no amount of stirringwould cause any more salt to go into solution. But if youheat the water to 100° F., more salt can be dissolved intothe solution. This dissolving action is known as directsolubility. But if you reaccomplish these steps usingcalcium saturates instead of table salt, you would seemore solids precipitate out of the solution as the heat isincreased. This action is suitably called reverse solubilityand occurs in a water-cooled condenser cooling tower.

3. You will find that scale will form on heattransfer surfaces when you use water containing even asmall amount of hardness. The pH value of the waterdetermines if the hard water will cause scale or corrosion.The pH scale is from 0 to 14. Neutral water has a pHvalue of 7.0. Any reading under 7.0 is acid, while areading above 7.0 is base or alkaline.

4. Let us compare pH to temperature. Athermometer measures the temperature of a solution,while pH measures the intensity of acid or base in asolution. As you know, pH means potential hydrogen.When a hydrogen atom has lost its electron (H+), itbecomes a positive hydrogen ion. When a great many ofthese hydrogen atoms make this change, the solution willbecome highly acid and attack metals. When thehydrogen atom gains electrons, the solution will be baseand have a pH value from 7.1 to 14. A base solutioncontains more hydroxyl ions (OH-). Scale will formwhen a base solution is exposed to a temperature rise,providing the hardness is 200 parts per million or higher.Notice the recommended pH for cooling towers in figure69.

5. You will find that it is very important to test forsolids in the water because solid content (hardness)determines the amount of scale formation. Hardness isthe amount of calcium and magnesium compounds insolution in the water. Water containing 200 p.p.m.hardness and a pH indication of 9 or above will enhancethe formation of scale. To avoid scale in cooling towers,you must control hardness. The maximum p.p.m.standards for cooling towers are

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Figure 69. pH scale.

100 p.p.m. for makeup water and 200 p.p.m. for bleedoffwater.

6. In cooling towers and evaporative condensersthe water becomes harder due to evaporation. The termused to compare hardness to the circulating water to themakeup water is cycles of concentration. For example, 2cycles of concentration indicate that the circulating wateris twice as hard as the makeup water. If the makeupwater contained 100 p.p.m., the circulating water wouldcontain 200 p.p.m. To avoid this damagingconcentration, you will find it is necessary to limit thecycles of concentration. Bleedoff is an effective methodused for this purpose. The amount of bleedoff can becalculated by using the following formula: Cycles of concentration

= bleedoff hardness (circulating water)makeup hardness

For example: if the bleedoff (circulating water) is 150p.p.m. and the makeup is 50 p.p.m., the cycles ofconcentration are 3.

7. There are many methods of treating water toprevent scale. A few of these are:

• Bleedoff-regulate the amount of bleedoff water tokeep the cycles of concentration within tolerance.

• pH adjustment-maintain the pH of the waterbetween 7 and 9, as near 8 as possible.

• Add polyphosphates-keeps scale formingcompounds in solution.

• Zeolite water softening-exchanges a nonscaleforming element for calcium and magnesiumcompounds.

Before we discuss water softening, we will introduce thesoap hardness test.

8. Soap Hardness Test. The soap hardness test isused to measure total hardness. The presence of calciumand magnesium salts, and to a lesser degree otherdissolved minerals, constitutes hardness in water.Hardness can be best determined by soap titration. Soap

titration directly measures the soap-consuming capacity ofa water. You will study this test in the followingparagraphs.

9. To begin the soap hardness test, measure 50milliliters of the sample water into the hardness testingbottle. Add the standard soap solution to the water, 0.5ml. at a time, from the soap burette, shown in figure 70.Shake bottle vigorously after each application and place iton its side. If no lather forms, continue adding 0.5-ml.portions of soap solution to a maximum of 6 ml andplace the bottle on its side. Now you must use theformula below if you have a permanent lather tocomplete the test. If a permanent lather does not appear,see para 10. Hardness (p.p.m.)

= 20 X(total number or ml. of standardsoap solution required forpermanent lather)

10. If a permanent lather does not appear afteradding 6 ml. of the standard soap solution,

Figure 70. Soap hardness test equipment.

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Figure 71. Accelator.

repeat the test with a new water sample. This time dilute25 ml. of the sample water with an equal quantity ofzero-hardness water (distilled water). Conduct the test asyou studied previously. When a permanent lather hasbeen obtained, calculate the hardness as follows:

= 40 X(total number of ml. of standardsoap solution required forpermanent lather)

11. Water Softening. Hard waters are potable butare objectionable because they form scale inside ofplumbing and on metal system components. Atemporary hardness can be caused by magnesiumbicarbonate. Hard water can be softened by twodifferent methods. The first is the lime-soda processwhich changes calcium and magnesium compounds fromsoluble to insoluble forms and then removes theseinsolubles by sedimentation and filtration. The secondand most common is zeolite or base-exchange process.This process replaces soluble calcium and magnesiumcompounds with soluble sodium compounds.

12. Lime-soda process. Lime-soda process plants areessentially the same as water filtration plants. Lime andsoda ash are added to raw water; the softening reactionoccurs during mixing and flocculation. The precipitatedcalcium and magnesium a removed by sedimentation andfiltration. An additional process, called recarbonation,which is the introduction of carbon dioxide gas, isfrequently applied immediately prior to filtration. If theraw water has high turbidity, the turbidity is partial removed by sedimentation prior to the adding ofthe lime and soda.

13. Zeolite process. The zeolite process is usuallyused for water which has low turbidity and does notrequire filtration. Treatment may be given to the entiresupply at one point. This system is commonly used tosoften water for special uses, such as for the control ofscale. In such cases, the treatment units are located atpoints near the equipment requiring treated water.

14. Turbidity is a muddy or unclear condition ofwater which is caused by suspended silt, clay, sand, ororganic materials such a decaying vegetation or animalwaste. Turbidity can be corrected by sedimentation,filtration, or traps. In most cases the water supply andsanitation personnel will supply you with usable, potablewater.

15. Softening devices. Softening devices includepatented equipment such as the Accelator and Spiractor.The Accelator is also used as a combined flocculation andsedimentation unit without softening. When this unit isoperated before filtration to treat water with lowsuspended solids and low alkalinity, it may be necessaryto add lime or clay to add weight and prevent rising floc.

16. The Accelator, shown in figure 71, is asuspended solid clarifier. Precipitates which are formedare kept in motion by a combination of mechanicalagitation and hydraulic flow. Velocity of waterflowthrough the system is controlled to keep precipitates insuspension at a level where water passes through them.The accumulated

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Figure 72. Spiractor

precipitate is called the sludge blanket. When theAccelator is operating properly, the water above thesludge blanket and flowing over the weirs is clear.Operation depends on balancing the lift of particles bythe velocity of upward flowing water against the pull ofgravity. When the velocity of the water is graduallydecreased, a point is reached at which the particles aretoo heavy to be supported by the velocity of the water.Continuous treatment builds up the sludge blanket whichis drawn off as required. Operation of the equipment iscovered in detail in the manufacturer’s instructionmanuals.

17. The Spiractor, shown in figure 72, consists of aninverted conical tank in which the lime-soda softeningreactions take place in the presence of a suspended bedof granular calcium carbonate. In operation, the tank isslightly more than half filled with 0.1 to 0.2 millimetergranules. Hardwater and chemicals enter the bottom ofthe unit close to each other. They mix immediately asthe treated stream of water rises through the granular bed

with a swirling motion. The upward velocity keeps thegranular material in suspension. As the water rises,velocity decreases to a point where material is no longerin suspension. The contact time, 8 to 10 minutes, isenough to complete softening actions. Softened water isdrawn off from the top of the cone. The size of calciumcarbonate granules increases during the process,increasing the bulk of granules in the unit. The waterlevel of the cone is kept down to the desired point bywithdrawing the largest particles from the bottom. Newmaterial must be added, which can be produced byregrinding and screening the discharged material.Softened water is usually filtered through a sand filter tomove turbidity. Advantages of the equipment are itssmall size, low installation cost, rapid treatment lack ofmoving parts and pumping equipment, and elimination ofsludge disposal problems. The unit is most effectivewhen hardness is predominantly calcium, there is lessthan 17 p.p.m. magnesium hardness (expressed ascalcium carbonate), water temperature is about 50° F.,and turbidity is less than 5 p.p.m.

18. Zeolite (ion exchange). Ion exchange is achemical operation by which certain minerals that areionized or dissociated in solution are exchanged (and thusremoved) for other ions that are contained in a solidexchange medium, such as a zeolite sandbed. Anexample is the exchange of calcium and magnesium, insolution as hardness in water, for sodium contained in asodium zeolite bed. The zeolites used in the process ofion exchange are insoluble, granular materials. A zeolitemay be classified as follows: glauconite (or green sand),precipitated synthetic, organic (carbonaceus), syntheticresin, and clay. Various zeolites are used, depending onthe type of water treatment required. Most zeolitespossess the property cation, or base exchange, but anionexchangers are also available and may be used whendemineralization of water is required. In the course oftreating water, the capacity of the zeolite bed to exchangeions is depleted. This depletion requires the bed to beregenerated by the use of some chemical that containsthe specific ion needed for the exchange. For instance,when a sodium zeolite is used to soften water byexchanging the sodium ion for the calcium andmagnesium ions of hard water, the zeolite graduallybecomes depleted of the sodium ion. Thus, it will nottake up the calcium and magnesium ions from the waterpassing through the bed. The sodium ion is restored tothe zeolite by uniformly distributing a salt or brinesolution on top of the bed and permitting it to passevenly down through the bed. The salt removes thecalcium and magnesium taken up by the bed as solublechlorides and restores the zeolite to its original condition.Beds may also be regenerated with acid, sodiumcarbonate,

80

sodium hydroxide, or potassium permanganate, dependingon the type of zeolite being used.

19. In addition to the problem of scale, therefrigeration man knows that corrosion is a constantproblem. Let us now study corrosion, its causes, itseffects, and its control.

22. Corrosion1. In the refrigeration/air-conditioning field,

corrosion has long been a problem. Even in the modernmissile complexes, corrosion is prevalent. Corrosion isvery difficult to prevent, but it can be controlled. Beforewe can control corrosion, we first must understand whatcauses it.

2. The effects of corrosion differ as to the type ofcorrosion, such as uniform, pitting, galvanic, erosion-corrosion, and electrochemical. We must understandvarious ways of treating the system to control these typesof corrosion. Corrosion is generally more rapid in liquidswith a low pH factor than in alkaline solutions.

3. Types of Corrosion. An air-conditioning systemmay have several types of corrosion in the water system.Many of these types are undoubtedly familiar to you.

4. Uniform corrosion. One of the most commontypes of corrosion encountered in acid environments isknown as uniform corrosion. This is caused by acids,such as carbonic, which cause a uniform loss of metalthroughout the condensating water system.

5. Pitting corrosion. Pitting corrosion is anonuniform type, the result of a local cell actionproduced when a particle, flake, or bubble of gasdeposited on a metal surface. The pitting is a localaccelerated attack, which causes a cavity in the metal butdoes not affect the surrounding metal. Oxygendeficiency under such a deposit sets up an anodic action.This area keeps producing such action until thepenetration finally weakens the structure and it falls,developing a pinhole leak.

6. Galvanic corrosion. When dissimilar metalswhich are capable of carrying electric current are presentin a solution, galvanic corrosion occurs. This action issimilar to the electroplating process used in industry tobond or plate dissimilar metals. When two metals similarto each other are joined together, there is little reaction.But the coupling of two metals from different groupscauses accelerated corrosion in one of the two metals.When using large amounts of copper in a system and afew unions of steel, the steel will corrode at a rapid rate.In such cases you should install nonferrous metal insteadof steel. Corrosion inhibitors reduce the corrosion ratebut will not eliminate galvanic corrosion.

7. Erosion-corrosion. Erosion-corrosion is caused bysuspended matter or air bubbles in a rapidly movingwater. The matter can be fine to coarse sand, dependingon the velocity of the water. Usually the greatest amountof erosion-corrosion will take place at elbows and U-bends. Another place where erosion-corrosion takes placeis on the impellers of centrifugal pumps.

8. Good filtration installations will remove grainsof sand and other matter that are large enough to causeerosion-corrosion. To get rid of air tapped in a system, itis recommended that hand- or spring-operated bleedvalves be installed in the highest point of the watersystem. Purging the water system gets rid of the airbubbles that enter the system in the makeup water.

9. Electrochemical corrosion. Electrochemicalcorrosion occurs when a difference in electrical potentialexists between two parts of a metal in contact with anelectrolyte (water). The difference in potential will causeelectric current to flow. The difference in potential maybe set up by two dissimilar metals, by a difference intemperature or amount of oxygen, or by theconcentration of the electrolyte at the two points ofcontact with the metal. The anode is the point at whichthe current flow is from the metal to the electrolyte; it ishere that corrosion occurs. The cathode, which is usuallynot attached, is the point of current flow from theelectrolyte to the metal. This action is shown in figure73.

10. Corrosion Inhibitor. The most commonchemicals used as inhibitors are chromates andpolyphosphates. These inhibitors alone serve only todecease the rate of corrosion, but if other watertreatments are used in conjunction with them, corrosionmay be nearly stopped.

11. Chromates. Chromates are seldom present nuntreated water; however, they may occur as a result ofindustrial waste contamination. The chromates are usedextensively to inhibit corrosion and are effective in thewater air-conditioning systems in concentrations of 200-500 p.p.m. at a pH of 7.0 to 8.5. Chromates are themost commonly used corrosion inhibitors in chilled watersystems. For corrosion prevention the most favorablerange is with the pH from 7.5 to 9.5, but scaling becomesa problem at the higher pH range. Consequently, the pHshould be held near the lower range where corrosionprotection is excellent. Because it is more economical,sodium bichromate (Na2Cr2O72H2O) is the mostcommonly used chromate compound. Sodium chromate(Na2CrO4) is also used widely.

12. Chromate concentration is stated in p.p.m.

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Figure 73. Causes and effects of corrosion.

Chromates are anodic inhibitors but can intensify pittingif they are used in insufficient amounts. Field tests mustbe performed to be sure the required amount ofchromate is in the water, and to check the pH.Corrosion is greatest when the pH is between 0 to 4.5.

13. Chromate concentration is tested by colorcomparison. The color of the treated water is matchedagainst a known chromate disc. For example, if thesample of treated water matches a tube known to contain200 p.p.m. of chromate, the sample would also contain200 p.p.m. of chromate.

14. Polyphosphates. Phosphates, particularly thepolyphosphates, are used in cooling water treatment. Theability to prevent metal loss with polyphosphate treatmentis inferior to the chromate treatment previously discussed.In addition, pitting is more extensive withpolyphosphates. Unlike chromate, high polyphosphateconcentrations are not practical because of theprecipitation of calcium phosphate.

15. One advantage of using polyphosphates is thatthere is no yellow residue such as produced by chromates.This highly undesirable residue is often deposited onbuildings, automobiles, and surrounding vegetation by thewind through cooling towers or evaporative condensers,when the system is treated by chromates. Also,polyphosphate treatment reduces corrosion products(sludge and rust) known as tuberculation.

16. A factor limiting the use of polyphosphates in

cooling water systems is the reversion of polyphosphatesto orthophosphates. Orthophosphates provide lessprotection than polyphosphates, and orthophosphatesreact with the calcium content of the water andprecipitate calcium phosphate. This precipitation formsdeposits on heat exchanger surfaces. The reversion ofpolyphosphates is increased by long-time retention andhigh water temperatures. Bleedoff must be adjusted onthe condenser water system to avid exceeding thesolubility of calcium phosphate.

17. The test used to determine the amount ofpolyphosphates in the system is similar the chromatecolor comparison test.

18. Corrosion inhibitor feeders. Many times a simplebag will be used to feed the chemicals into the water.The chemicals, in pellet or crystal form, are placed innylon net bags and hung in the cooling tower sump.However, chilled water and brine systems require the useof a pot type feeder similar to the feeder shown in figure74.

19. The chemical charge is prepared by dissolvingthe chemicals in a bucket and then filling the pressuretank (F) with the solution. Valves B and C are closed,and valve A is opened to drain the water out of the tank.After the water is drained, close valve A and open valvesD and E. Then fill tank (F) with the dissolved chemicalsolution. Opening valves B and C after you have closedvalves D and E will place the feeder in operation. Thefeedwater from the discharge

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Figure 74. Pot type feeder.

side of the pump with force the solution into tie suctionside of the pump. Within a few minutes, the solutionwill be washed out of the tank. This feeder isnonadjustable.

20. Another type of feeder you may use is the pottype proportional feeder. This type, similar to the oneshown in figure 74, has an opening to permit chargingwith chemicals in briquette or lump form. A portion ofthe water to be treated is passed through the tank,gradually dissolving the chemicals.

21. The degree of proportionality is questionable attimes, because there is little control over the solution rateof the briquettes or the chemical incorporated in them.Although this system is classified as proportional, itcannot be used where accuracy of feed is required. It isused successfully in our application because we have alarge range in p.p.m. to control-for example, 250-300p.p.m. chromate.

22. Now that we have studied corrosion andcorrosion control, let’s discuss algae.

23. Algae

1. Algae are slimy living growth of one-celledanimals and plants. They may be brought by birds orhigh

winds. Algae thrive in cooling towers and evaporativecondensers, where there is abundance of sunlight andhigh temperatures to carry on their life’s processes. Algaeformations will plug nozzles and prevent properdistribution of water, thus causing high condensingpressures and reduced system efficiency. In relation tothe larger subject of algae, we will study residual chlorinetests, chlorine demand tests, pH determination, pHadjustment, chlorine disinfectants, hypochlorination, andchlorination control.

2. Residual Chlorine Test. The growth of algae iscontrolled by chlorination. The residual chlorine test isthe test that we make to determine the quantity ofavailable chlorine remaining in the water after satisfactionof the chlorine demand has occurred. Orthotolidine isthe solution used in making the residual chlorine test.This solution reacts with the residual chlorine, taking ona color which is matched against a standard color in thecomparator disc. Readings up to 5 p.p.m. may be readfrom the comparator disc. One p.p.m. will control algaeand 1.5 p.p.m. will kill algae.

3. The time required for full development of color byorthotolidine depends on the temperature and kind ofresidual chlorine present. You will find that the colorwill develop several times faster when water is at 70° F.than when it is near the freezing point. For this reason,you must warm up cold samples quickly after mixing thesample with orthotolidine. Simply holding the sampletube in your hand is sufficient.

4. For samples containing only free chlorine,maximum color appears almost instantly and begins tofade in a minute. You must take the reading atmaximum color intensity. However, a longer period isrequired for full color development of chloramines whichmay be present. Since samples containing combinedchlorine develop their color at a rate primarily dependentupon temperature and to a lesser extent on the quantityof nitrogenous material present, observe the samplesfrequently and use their maximum value.

5. At 70° F. the maximum color develops in about3 minutes, while at 32° F. it requires 6 minutes. Themaximum color starts to fade after about 1½ minutes.Therefore, in the orthotolidine-arsenite (OTA) test, thewater temperature should be about 70° F and the sampleread at maximum color and in less than 5 minutes.Preferably, permit the color to develop in the dark. Readthe sample frequently to insure observation of maximumcolor.

6. Use enough chlorine so that the residual

83

in the finished water after 30 minutes of contact timewill be as follows:

These residuals are effective for water temperaturesranging from 32° to 77° F. Bactericidal efficiency ofchlorine increases with an increase in water temperature.

7. Two types of residual chlorine have beenmentioned. The first is the free available chlorine whichcan be measured by the OTA test. It is valuable becauseit kills algae quickly. The second is the combinedavailable chlorine, produced by the chloramines, a sloweracting type and therefore one which requires a higherconcentration to achieve an equivalent bactericidal effectin the same contact time.

8. The orthotolidine-arsenite (OTA) test is thepreferable one in determining chlorine residuals since itpermits the measurement of the relative amounts of freeavailable chlorine, combined available chlorine, and colorcaused by interfering substances. The test is bestperformed in a laboratory because the accuracy of theresults is dependent upon the quantity of availablechlorine preset, the adherence to time intervals betweenthe addition of reagents and the temperature of thesample. With water temperatures above 68° F, theaccuracy decreases, whereas below this temperature, itincreases.

9. The free available chlorine residual subtractedfrom the total residual chlorine would equal thecombined available residual. You recall that thecombined available residual is actually that slower actingresidual created by the chloramines which have formedin the water. Since the OT test measures only the totalavailable chlorine residual, it impossible to determine thecombined available chlorine residual with this test. Withthe orthotolidine test, both the free and combinedavailable chlorine are measured. If it is desired todetermine whether the residual is present in either thefree or combined form, it is necessary to employ theorthotolidine-arsenite test.

10. Chlorine Demand Test. The chorine demand ofwater is the difference between the quantity of chlorineapplied in water treatment and the total available residualchlorine present at the end of a specified contact period.The chlorine demand is dependent upon the amount ofchlorine applied (amount applied is dependent upon thefree available and combined available chlorine), thenature and the quantity of chlorine-consuming agents

present, the pH value, and the temperature of the water.Remember that the high pH and low temperature retarddisinfection by chlorination. For comparative purposes, itis imperative that all test conditions be stated, such aswater sample temperature or room temperature.

11. The smallest amount of residual chlorineconsidered to be significant is 0.1 mg/1 Cl. Some of thechlorine-consuming agents in the water arenonpathogenic, but they contribute to the total chlorinedemand of the water just as other agents do.

12. Chlorine demand in most water is satisfied 10minutes after the chlorine is added. After the first 10minutes of chlorination, disinfection continues but at adiminishing rate. A standard period of 30 minutes ofcontact time is used to insure that highly resistantorganisms have been destroyed, provided that a highenough dosage has been applied.

13. The chlorine demand test is used as a guide indetermining how much chlorine is needed to treat agiven water. Briefly, the test consists of preparing ameasured test dosage of chlorine, adding it to a sample ofthe water to be treated, and adding the resultant residualafter 30 minutes of contact time. The required dosage isthen computed; it is the chlorine needed to equal thesum of the demand plus the minimum contact residual.

14. To determine the chlorine demand, calciumhypochlorite, containing 70 percent available chlorine, isused for the test. Mix 7.14 grams of calciumhypochlorite (Ca(OCL)2) with 1000 cc. of the best wateravailable to produce 5000 p.p.m. chlorine solution. Onemilliliter of this standard solution (reagent), when addedto 1000 cc. of the water to be tested, equals 5 p.p.m.chlorine test dosage. Thus, with 1 milliliter of thereagent equaling 5 p.p.m., any proportionate test dosagemay be arrived at by using one-fifth, 0.2 ml., of thereagent in 1000 cc. of the water for each p.p.m. ofchlorine dosage desired. After adding a test dosage of aknown strength of a 1000-cc. sample of the water to betested (5 p.p.m., or 1 ml. of the reagent is normally used),wait 30 minutes and run a chlorine residual test. Yousubtract the chlorine residual from the test dosage toobtain the chlorine demand.

15. If you do not obtain a residual after a 30-minuteperiod, the test is invalid and must be repeated. Youincrease the reagent by 5 p.p.m. each time until a residualis obtained. If, for example, the test were repeated twotimes, the results would be recorded as follows:

16 pH Determination. The pH determination

84and residual chlorine tests are both made with the colorcomparator. Knowing the pH value of water is importantfor several reasons. First, the pH value influences theamounts of chemicals used for coagulation. Second, thedisinfecting action of chlorine (to control algae) isretarded by a high pH. If pH is above 8.4, the rate ofdisinfection decreases sharply. Third, the corrosion rateis lowest at a pH of 14, increases to a pH of 10, andremains essentially uniform until a pH of 4.3 is reached,when it increases rapidly.

17. But, how do you determine the pH value ofwater with the comparator? Three indicator solutions aresupplied for making pH determinations with thecomparator. Bromcresol purple green is used for the pHrange from 4.4 to 6.0. Bromthymol blue is used for pHvalues from 6.0 to 7.6. Cresol red-thymol blue is usedfor pH values from 7.6 t 9.2. Standard color discscovering each range are supplied with the comparator.Generally, the bromthymol blue indicator is used firstsince most pH values fall within its range. The readingsfor pH are made immediately after adding the indicator.You should keep in mind that clorimetric indicatorsprovide sharp changes in readings over a short span ofthe pH range, but once the end of the range has beenreached, little change in color is noted even though aconsiderable change in pH takes place. For this reasonreadings of 5.8 to 6.0, obtained when using thebromcresol purple green indicator, should be checked bytaking a reading with bromthymol blue. Similarly, pHreadings of 7.6 to 7.8 on the cresol red-thymol blue discshould be checked on the bromthymol blue disc.

18. To determine the pH value, fill the tubes to themark with the water sample. Add the indicator solutionto one tube in the amount specified by the manufacturer,usually 0.5 ml. (10 drops) for a 10-ml. sample tube andproportionally more for larger tubes. Mix the water andindicator and place the tube in the comparator.

19. After you place the tube in the comparator, youmatch for color and read pH directly. If the color is ateither the upper or lower range of the indicator selected,repeat the test with the next higher or lower indicator.

20. If a color comparator is not available, methylorange and phenolphthalein indicators may be used tomake an approximate pH determination. Theseindicators are used primarily for alkalinity determinations,but they can be used for a rough check of pH values.

21. To determine a low pH that is around 4.3, fill atest bottle to the 50-ml. mark with a sample of the waterto be tested and add 2 drops of methyl orange indicator.Observe the test bottle against a white background andinterpret the color thus: pinkish red, pH below 4.3;yellow, pH above 4.3.

22. To determine a high pH that is around 8.3, fill atest bottle to the 50-ml. mark and add 2 drops ofphenolphthalein indicator. Observe the test bottle againsta white background and interpret thus: pink, pH above8.3; colorless, pH below 8.3.

23. pH Adjustment. Caustic soda, soda ash, andsodium hydroxide can be added to water to increase thepH. The caustic soda or sodium hydroxide treatmentuses a solution feeder to add the chemical. This is thetype of feeder used to chlorinate water for algae control.Soda ash is added by means of a proportioning pot typefeeder. The amount you would add depends upon thepH of the water. Test the water frequently while addingthese chemicals and stop the treatment when the desiredpH level is reached.

24. Acids are added to lower the pH. The typesused are sulphuric, phosphoric, and sodium sulfate. Theyare added through solution feeders. Add only enoughacid to reduce the pH (alkalinity) to the proper zone.The zone is usually 7-9 pH, preferably a pH of 8.

25. Chlorine Disinfectants. Chlorine disinfectantsare available in a number of different forms. The twoforms that we will use are calcium and sodiumhypochlorite.

26. Calcium hypochlorite. Calcium hypochlorite, Ca(OCl)2, is a relatively stable, dry granule or powder inwhich the chlorine is readily soluble. It is prepared undera number of trade names, including HTH, Perchloron,and Hoodchlor. It is furnished in 3- to 100-poundcontainers and has 65 to 70 percent of available chlorineby weight. Because of its concentrated form and ease ofhandling, calcium hypochlorite is preferred over otherhypochlorites.

27. Sodium hypochlorite. Sodium hypochlorite,NaOCl, is generally furnished as a solution that is highlyalkaline and therefore reasonably stable. Federalspecifications call for solutions having 5 and 10 percentavailable chlorine by weight. Shipping costs limit its useto areas where it is available locally. It is so furnished aspowder under various names, such as Lobax and HTH-I5.The powder generally consists of calcium hypochloriteand soda ash, which react in water to form sodiumhypochlorite.

28. Hypochlorinators. Hypochlorinators, orsolution feeders, introduce chlorine into the water supplyin the form of hypochlorite solution. They are usuallymodified positive-displacement piston or diaphragmmechanical pumps. However, hydraulic displacementhypochlorinators are also used. Selection of a feederdepends on local

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conditions, space requirements, water pressure conditions,and supervision available. Fully automatic types areactuated by pressure differentials produced by orifices,venturis, valves, meters, or similar devices. They can alsobe used to feed chemicals for scale and corrosion control.Common types of hypochlorinators are described below.

29. Proportioneers Chlor-O-Feeder. TheProportioneers Chlor-O-Feeder is a positive-displacementdiaphragm type pump with electric drive (fig. 75) orhydraulic operating head (fig. 76). Maximum capacity ofthe most popular type, the heavy-duty midget Chlor-O-Feeder, is 95 gallons of solution in 24 hours.

30. a. Semiautomatic control. The motor-driventype may be cross connected with a pump motor forsemiautomatic control. The hydraulic type can besynchronized with pump operation by means of asolenoid valve.

31. b. Fully automatic control. Motor-driven typesare made fully automatic by use of a secondary electricalcontrol circuit actuated by a switch inserted in a disc orcompound-meter gearbox. This switch closesmomentarily each time a definite volume of water passesthrough the meter, thus starting the feeder. A timingelement in the secondary circuit shuts off the feeder aftera predetermined number of feeder strokes; the numberof strokes is adjustable. In the hydraulic type, shown infigure 77, the meter actuates gears in a Treet-O-Controlgearbox which in turn controls operation of a pilot valvein the water or air supply operating the feeder. Thedosage rate is controlled by waterflow through the meter,thus automatically proportioning the treatment chemical.Opening and closing frequency of the valve thusdetermines frequency of operation of the Chlor-O-Feeder.

32. Wilson type DES hypochlorinator. The Wilsontype DES hypochlorinator is a constant-rate, manuallyadjusted, electric-motor-driven, positive-displacementreciprocating pump for corrosive liquids, and is shown infigure 78. Maximum capacity is 120 gallons of solutionper day. This unit is a piston pump with a diaphragmand oil chamber separating the pumped solution from thepiston to prevent corrosion of working parts.

33. Model S hypochlorinator (manufactured by PrecisionChemical Pump Corporation). The Model Shypochlorinator, shown in figure 79, is a positive-displacement diaphragm pump with a manually adjustablefeeding capacity of 3 to 60 gallons per day. A motor-driven eccentric cam reciprocates the diaphragm, injectingthe solution into the main supply. Use of chemicallyresistant plastic and synthetic rubber in critical partscontributes to long operating life.

34. Chlorination Control. To estimate dosagewhen no prior record of chlorination exists or wherechlorine demand changes frequently:

(1) Determine chlorine demand, or start chlorinefeed at a low rate and raise feed by small steps; at thesame time make repeated residual tests until a trace isfound. Observe rate of flow treated and rate of chlorinefeed at this point. Chlorine demand then equals dosageand is determined from the following equation:

(2) Add the minimum p.p.m. required residual tothe p.p.m. demand in order to estimate the p.p.m. dosagerequired to obtain a satisfactory residual. Then setchlorinator rate of feed in accordance with the aboveestimated p.p.m dosage. Further upward adjustment aftermaking residual tests is usually required because thedemand increases as the residual is increased.

35. Rate of feed of hypochlorinators is found fromthe loss in volume of gallons of solution by determiningchange in depth of solution in its container. Knowingthe solution strength, the pounds of chlorine used can becalculated:

36. Available chlorine content of the chlorinecompound used must be known in order to calculate therate of hypochlorite-solution feed. Available chlorine isusually marked on the container as a percentage ofweight. Values generally are as follows: Calcium hypochlorite .........................70 percent Sodium hypochlorite (liquid) ..............10 percent (varies)

(1) To find the actual weight of chlorine compoundto be added, use the equation:

(2) To find the amount of 1-percent dosing solutionneeded to treat a given quantity of water with desireddosage, use the equation:

(3) To prepare various quantities of 1-percent dosingsolution, use the amounts given table 20.

(4) To find the rate of feed of chlorine in gallonsper day, use the equation:

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TABLE 20

(5) To feed the pounds of chlorine compoundneeded to prepare dosing solution of a desired strength,use the equation:

(6) To find the gallons of hypochlorite stocksolution needed to prepare dosing solution of a requiredstrength, use the equation:

37. CAUTION: Make dosing solutions strongenough so that the hypochlorinator can be adjusted tofeed one-half its capacity per day or less. Avoid using acalcium hypochlorite dosing solution stronger than 2percent, even if it is necessary to set the machine to feedits full day capacity. If calcium hypochlorite solutionstronger than 2 percent is required when the feed is set amaximum, small amounts of sodium hexametaphsphatein the solution will permit maximum concentrations upto 5 percent. Solutions of sodium hypochlorite may befed in greater concentrations.

38. Another problem area besides algae is turbidwater, so let’s now study turbidity.

24. Turbidity

1. Turbidity in water is caused by suspended matterin a finely divided state. Clay, silt, organic matter,microscopic organisms, and similar materials arecontributing causes of turbidity.

2. While the terms “turbidity” and “suspendedmatter” are related, they are not synonymous. Suspendedmatter is the amount of material in a water that can beremoved by filtration. Turbidity is a measurement of theoptical obstruction of light that is passed through a watersample.

3. Turbid makeup water to cooling systems may

cause plugging and overheating where solids settle out onheat exchanger surfaces. Corrosive action is increasedbecause the deposits hinder the penetration of corrosioninhibitors. We will cover the Jackson turbidity test andturbidity treatment.

4. Turbidity Test. The Jackson candleturbidimeter is the standard instrument used for makingturbidity measurements. It consists of a graduated glasstube, a standard candle, and a support for the candle andtube. The glass tube and the candle must be placed in avertical position on the support so that the centerline ofthe glass tube passes through the centerline of the candle.The top of the support for the candle should be 7.6centimeters (3 inches) below the bottom of the tube.The glass tube must be graduated, preferably to readdirect in turbidities (p.p.m.), and the bottom must be flatand polished. Most of the tube should be enclosed in ametal or other suitable case when observations are beingmade. The candle support will have a spring or otherdevice to keep the top of the candle pressed against thetop the support. The candle will be made of beeswaxand spermaceti, gauged to burn within the limits of 114to 126 grains per hour.

5. Turbidity measurements are based on the depthof suspension required for the image of the candle flameto disappear when observed through the suspension. Toinsure uniform results, the flame should be kept aconstant size and the same distance below the glass tube.This requires frequent trimming of the charred portion ofthe candle wick and frequent observations to see that thecandle is pushed to the top of its support. Each timebefore lighting the candle, remove the charred part of thewick. Do not keep the candle lit for more than a fewminutes at a time, for the flame has a tendency toincrease in size.

6. The observation is made by pouring thesuspension into the glass tube until the image of thecandle flame just disappears from view. Pour slowlywhen the candle becomes only faintly visible. After theimage disappears, remove 1 percent of the suspensionfrom the tube; this should make the image visible again.Care should be taken to keep the glass tube clean on both

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Figure 75. Proportioneers heavy-duty midget Chlor-O-Feeder.

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Figure 76. Hydraulically driven hypochlorinator.

Figure 77. Motor-driven hypochlorinator.

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Figure 78. Wilson type DES hypochlorinator.

the inside and the outside. The accumulation of soot ormoisture on the bottom of the tube may interfere withthe accuracy of the results. The depth of the liquid isread in centimeters on the glass tube, and thecorresponding turbidity measurement is recorded in partsper million.

7. Turbidity Treatment. Filtration is the mostcommon method for removing suspended matter thatyou will encounter. Coagulants, flocculators, andsedimentation basins are also used but are more commonto large water treatment facilities.

8. Sand and anthracite coal are the materialscommonly used as filter media. The depth of the filterbed can range up to 30 inches, depending upon the typeof filter you will be using. You will find that quartzsand, silica sand, and anthracite coal are used in mostgravity and pressure type filters.

9. Gravity filters. As the name implies, the flow ofwater through the filter is obtained through

Figure 79. Model S hypochlorinator.

gravity. These filters are not common to our career fieldbecause coagulants and flocculation are required beforeeffective filtration can occur.

10. Pressure filers. Pressure filers are more widelyused because they may be placed in the line underpressure and thus eliminate double piping.

11. Pressure filters may be of the vertical orhorizontal type. The filter shells are steel, cylindrical inshape; with dished heads. Vertical filters range indiameter from 1 to 10 feet, with capacities from 2.4g.p.m. to 235 g.p.m. at a filtering rate of 3 gals/sq.ft/min.Horizontal filters, 8 feet in diameter, may be 10 to 25feet long, with capacities from 210 g.p.m. to 570 g.p.m.

12. Filter operation. When you initially operate, oroperate the filter after backwashing it, you should allowthe filtered water to waste for a few minutes. Thisprocedure rids the system of possible suspended solidsremaining in the underdrain system after backwashingand also permits a small amount of suspended matter toaccumulate on the filter bed. As soon as the filterproduces clear water, the unit is placed in normal service.

13. During operation, the suspended matter removedby the filter accumulates on the surface of the filter. Aloss-of-head gauge indicates when backwashing isnecessary. Backwashing is necessary when the gaugereads 5 p.s.i.g.

14. Backwashing rates are much higher thanfiltration rates because the bed must be expanded and thesuspended matter washed away. This backwashing iscontinued for 5 to 10 minutes; then the filter is returnedto service.

15. We have discussed the testing and treatment ofwater to be used in our systems. To make

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valid tests and prescribe proper treatment, you mustunderstand the proper methods of water sampling.

25. Sampling

1. Frequent chemical and bacteriological analyses ortests of raw and treated water are required to plan andcontrol treatment and to insure a safe and potable water.Facilities needed for water analysis depend on the type ofsupply and treatment. They vary from a simple chlorineresidual and pH comparator to a fully equippedlaboratory. Our discussions here are not concerned withanalysis as such, since the term “analysis” implies that wecompletely disassemble water into its elementarycomposition. In complete water analysis your requiredtask is to obtain valid samples to be forwarded to theproper laboratories. The sampling and testing with whichyou personally are concerned are simple and consist onlyof routine type tests that can be made in the field or in abase laboratory with simple chemicals and comparatorequipment.

2. Sampling Methods. Sampling is an extremelyimportant operation in maintaining quality of watersupply. Unless the water sample is representative, testresults cannot be accurate. You must be very careful toobtain a sample that is not contaminated by any outsidesource, such as dirty hands, dirty faucets, dirty orunsterilized containers. Do not sabotage the entireoperation before it gets a good start. Follow approved,correct sampling methods like those outlined here anduse only chemically clean sample containers.

3. Chemical analysis. The following precautionsand actions are necessary when samples for chemicalanalysis are taken:

a. Wells. Pump the well until normal draw-downis reached. Rinse the chemically clean sample containerwith the water to be tested and then fill it.

b. Surface supplies. Fill chemically clean raw watersample containers with water from the pump dischargeonly after the pump has operated long enough to flushthe discharge line. Take the water sample from thepond, lake, or stream with a submerged sampler at theintake depth and location.

c. Plant. Take samples inside a treatment plantfrom channels, pipe taps, or other points where goodmixing is obtained.

d. Tap or distribution system. Let tap water runlong enough to draw the water from the main beforetaking samples.

e. Sample for dissolved gas test. Take care toprevent change in dissolved gas content during sampling.Flush the line; then attach a rubber hose to the tap andlet

the water flow until all air is removed from the hose.Drop the end of the hose to the bottom of a chemicallyclean sample bottle and fill gently, withdrawing the hoseas the water rises. Test for dissolved gas immediately.

4. Bacteriological analysis. In obtaining samples forbacteriological analysis, contamination of the bottle,stopper, or sample often causes a potable water supply tobe reported as nonpotable. Full compliance with allprecautions listed in the paragraphs below is necessary toassure a correct analysis.

a. Bottles. Use only sterilized bottles with glassstoppers. Cover the stopper and the neck of the bottlewith a square of wrapping paper or other guard to protectagainst dust and handling. Before sterilizing the samplebottle to be used to test chlorinated water, place 0.02 to0.05 gram of sodium thiosulfate, powdered or in solution,in each bottle to neutralize chlorine residual in sample.Keep the sterilization temperature under 392° F. toprevent decomposition of the thiosulfate.

b. Sampling from a tap. After testing for chlorineresidual, close the tap and heat the outlet with an alcoholor gasoline torch to destroy any contaminating materialthat may be on the lip of the faucet. Occasionally, extrasamples may be collected without flaming the faucet todetermine whether certain faucet outlets arecontaminated. Flush the tap long enough to draw waterfrom the main. Never use a rubber hose or othertemporary attachment when drawing a sample from thetap. Without removing the protective cover, remove thebottle stopper and hold both cover and stopper in onehand. Do not touch the mouth of the bottle or sides ofthe stopper. Fill the bottle three-quarters full. Do notrinse the bottle, since thiosulfate will be lost. Replace thestopper and fasten the protective cover with the samecare.

c. Sampling from tanks, ponds, lakes, and streams.When collecting samples from standing water, removethe stopper as previously described and plunge the bottle,with the mouth down and hold at about a 45° angle, atleast 3 inches beneath the surface. Tilt the bottle toallow the air to escape and to fill the bottle. When fillingthe bottle, move it in a direction away from the handholding it so water that has contacted the hand does notenter the bottle. After filling, discard a quarter of thewater and replace the stopper.

d. Transporting and storing samples. Biologicalchanges occur rapidly. Therefore, if the test is to bemade at the installation, perform the test within an hourif possible or refrigerate it and test within 48 hours. Ifthe sample is to be tested at a laboratory away from theinstallation,

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use the fastest means of transportation to get to thelaboratory.

e. Sample data. You must identify each sample.Note the sampling point, including building number andstreet location for sample of distribution system; sourceof water, such as installation water supply; and the dateof collection.

5. Laboratory Methods and Procedures forTesting. As you were told earlier in this section, analysisis an involved process beyond the scope of yourresponsibility. However, nonstandard testing, either in alaboratory or in the field, may comprise a part of yourdaily work. Since you are probably going to be workingin a base laboratory part of the time, laboratory techniqueare required knowledge. Some of the basic rules areoutlined in the following paragraphs.

6 Cleanliness. Chemical and bacteriological testscan easily be invalidated by impurities introduced into thetest by dirty hands, clothing, or equipment. Set up aregular daily schedule for cleaning laboratory equipment,furniture, and floors.

7. Personal safety. Keep hands away from yourmouth or eyes, especially when working with poisonouschemicals or bacteriological cultures. Keep a dilutedsolution of lysol or mercuric chloride and a bicarbonateof soda solution at or near the laboratory sink at alltimes. Rinse hands with this solution immediately afterwashing any bacteriological-culture glassware or acidcontainers. Then wash thoroughly with soap and water.Never smoke or eat in the laboratory. Drinking fromlaboratory glassware may result in serious illness if acontaminated beaker is used. Do not use laboratory toprepare food or use incubators or refrigerators to storefood.

Review Exercises

The following exercises are study aids. Write your answersin pencil in the space provided after each exercise. Use theblank pages to record other notes on the chapter content.Immediately check your answers with the key at the end of thetext. Do not submit your answers for grading.

1. What is the main scale-forming compoundfound in condensing water systems? (Sec 21,Par. 1)

2. Scale will form when the pH value is_________ ________to_________________ and the p.p.m. is__________________ or higher. (Sec. 21,Par. 4)

3. What are the cycles of concentration if themakeup water is 100 p.p.m. and the circulatingwater is 200 p.p.m.? (Sec. 21, Par. 6)

4. Give four methods of preventing scale. (Sec. 21,Par. 7)

5. During the soap hardness test you use 10 ml. ofstandard soap solution to obtain a permanentlather. What is the hardness of your sample?(Sec. 21, Par. 9)

6. Which softening process changes calcium andmagnesium from a soluble to an insoluble state?(Sec. 21, Par. 11)

7. How does the zeolite process soften water?(Sec. 21, Par. 11)

8. Why is it necessary to add lime or clay to theAccelator? (Sec. 21, Par. 15)

9. What factors would limit the use of theSpiractor? (Sec. 21, Par. 17)

10 What is used to restore the sodium ions in azeolite softener? (Sec. 21, Par. 18)

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11. In what type of liquid is corrosion more rapid?(Sec. 22, Par. 2)

12. What is the most common type of corrosion inan acid liquid? (Sec. 22, Par. 4)

13. Which type of corrosion is characterized bycavities and gradually develops into pinholeleaks? (Sec. 22, Par. 5)

14. If a system contains an abundance of copper anda few unions of steel, and the steel unions arecorroding at a very high rate, what type ofcorrosion is taking place? (Sec. 22, Par. 6)

15. What causes erosion-corrosion and what is usedto control this type of corrosion? (Sec. 22, Pars.7 and 8)

16. What are the two most common chemicalcorrosion inhibitors? (Sec. 22, Par. 10)

17. Chromates are most effective in air-conditioningwater systems when the concentration is_____________ to ___________ and thepH is ____________________. (Sec. 22,Par. 11)

18. What is the most common chromate used andwhy? (Sec. 22, Par. 11)

19. How is the chromate concentration of treatedwater measured? (Sec. 22, Par. 13)

20. Why shouldn’t high concentrations ofpolyphosphates be used? (Sec. 22, Par. 14)

21. Give two advantages using polyphosphates overchromates. (Sec. 22, Par. 15)

22. Why must bleedoff be adjusted on condenserwater systems when polyphosphates are used?(Sec. 22, Par. 16)

23. In what two forms may chemical corrosioninhibitors be that are placed in a nylon net bag,which in turn is placed in a cooling tower? (Sec.22, Par. 18)

24. What type of corrosion inhibitor feeders arerequired on chilled water and brine systems?(Sec. 22, Par. 18)

25. What are the effects of algae on the operationof an air-conditioning system? (Sec. 23, Par. 1)

26. How many p.p.m. of chlorine are needed toeliminate algae growth in a cooling tower? (Sec.23, Par. 2)

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27. (Agree)(Disagree) During the performance ofthe residual chlorine test, you must heat the

sample to 70° F. before adding the orthotolidine.(Sec. 23, Par. 3)

28. Why is chlorination an effective method of algaecontrol in cooling towers and evaporativecondensers? (Sec. 23, Par. 6)

29. Why is the orthotolidine-arsenite test preferredto the orthotolidine test? (Sec. 23, Par. 8)

30. What is the combined available chlorine residualwhen the free available chlorine residual is 2.5p.p.m. and the total residual chlorine is 3.25p.p.m.? (Sec. 23, Par. 9)

31. Describe the procedure used to perform thechlorine demand test. (Sec. 23, Pars. 13, 14, and15)

32. As the result of a pH determination with a colorcomparator, you have found the pH to be 7.7.How would you have reached this solution?(Sec. 23, Pars. 17, 18, and 19)

33. After you have added two drops ofphenolphthalein indicator to the sample, thesample turned pink. The sample is (acid,alkaline). (Sec. 23, Par. 22)

34. Which acids are used to lower the pH and howare they added to the water? (Sec. 23, Par. 24)

35. Why is calcium hypochlorite used more oftenthan sodium hypochlorite? (Sec. 23, Pars. 26and 27)

36. Which hypochlorinator would you select if thewater to be treated required 100 gallons ofchlorine solution per day? Why? (Sec. 23, Par32)

37. The dosage of chlorine added to the 0.5 milliongallons of water, when 20 pounds of chlorine isadded per day, is approximately______________ p.p.m. (solve to thenearest p.p.m.). (Sec. 23, Par. 34)

38. How many pounds of HTH would you have toadd to treat water which requires 30 pounds ofchlorine? (Solve to the nearest pound). (Sec.23, Pars. 35 and 36)

39. How many gallons of chlorine is added per dayto treat 2 million gallons of water when thedosage is 1.5 p.p.m. and the strength of thedosing solution is 10 percent? (Sec. 23, Par. 36)

40. What precautions must be followed while youare performing the Jackson turbidimeter test?(Sec. 24, Pars. 4, 5, and 6)

41. How many gallons of water can be filteredthrough a vertical type pressure filter in 1 hour?The diameter of the filter is 4 feet. (Sec. 24,Par. 11)

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42. What precautions for taking water samples iscommon to both chemical and bacteriologicalanalysis? (Sec. 25, Pars. 3 and 4)

43. How is a bottle sterilized when it is to be usedfor chlorine testing? (Sec. 25, Par. 4, a)

44. How far below the surface of the water in atank should you hold the bottle when taking asample? (Sec. 25, Par. 4,c)

45. What type of solution should you wash yourhands with after making water tests? (Sec. 25,Par. 7)

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CHAPTER 5

Centrifugal Water Pumps

IF YOU SWING a bucket of water around your head, thewater does not spill out because centrifugal force pressesit toward the bottom of the bucket. If a number ofbottomless buckets were whirled around inside a pipe,and there were only one hole where water could leavethe pipe, each pail would throw out some of its water asit passed this hole. It would also suck up more water atthe center. This is exactly how the centrifugal pumpworks. Instead of buckets, however, a centrifugal pumphas vertical ribs, or vanes, mounted on a revolving disc.The water takes up the space between the vanes, or ribs.The disc, as it revolves, forces water through the pumpoutlet to the various components the water serves.

2. In this chapter we will study installation,operation, and maintenance of centrifugal water pumps.

26. Installation

1. The installation of a centrifugal water pumpincludes laying a concrete foundation and aligning eachcomponent. The foundation should be sufficientlysubstantial to absorb any vibration and to form apermanent rigid support for the baseplate. Figure 80shows a foundation and baseplate. This type of concretefoundation is important in maintaining the alignment of adirectly driven unit. A mixture of 1 part cement, 3 partssand, and 6 parts gravel or crushed rock is recommended.In building the foundation, you should leave the topapproximately 1 inch low to allow for grouting. Youshould roughen and clean the top of the foundationbefore placing the unit on it. Foundation bolts of theproper size should be embedded in the concrete before itsets. Use a template or drawing to locate the bolts. Apipe sleeve about 2 diameters larger than the bolt is usedto allow movement for the final positioning of the bolts.Place a washer between the bolthead and the innersurface of the pipe to hold the bolt in position.

2. Be sure the foundation bolts are long enough toproject through the nuts one-fourth of a inch afterallowance has been made for grouting, for the thicknessof the bedplate, and for the thickness of the foundationbolt nut. We are now ready to install the pump unit.

3. Place wedges at four points, two below theapproximate center of the pump and two below theapproximate center of the motor. Some installations mayrequire two additional wedges at the middle of thebedplate. By adjustment of the wedges you can bring theunit to an approximate level and provide for the properdistance above the foundation for grouting. By furtheradjustment of the wedges you can bring the couplinghalves in reasonable alignment by tightening down thepump and motor holddown bolts.

4. Check the gap and angular misalignment on thecoupling. The coupling shown in figure 81 is the “spiderinsert” type. The normal gap is one-sixteenth of an inch.The gap is the difference in the space between thecoupling halves and the thickness of the spider insert.Angular misalignment may be checked by using calipersat four points on the circumference of the outer ends ofthe coupling hubs, at 90° intervals, as shown in figure 81.

5. The unit will be in angular alignment when themeasurements show the ends of the coupling hubs to bethe same distance apart at all four points. Gap andangular alignment is obtained by loosening the motorholddown bolts and shifting or shimming the motor asrequired. Tighten down the holddown bolts afteradjustments have been made.

6. After the wedges have been adjusted, tighten thefoundation bolts evenly but only finger-tight. Be sure youmaintain the level of the bedplate. Final tightening ofthe foundation bolts is done after the grout has set 48hours.

7. To grout the unit on the foundation, build awooden dam around the foundation, as shown in figure80, and wet the top surface of the concrete thoroughly.Now force the grout under the bedplate. The groutshould be thin enough to level out under the bedplate,but not so wet that the cement will separate from thesand and float

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Figure 80. Pump foundation.

to the surface. The recommended mixture for grout is 1part of Portland cement to 3 parts of sharp sand. Thegrout should completely fill the space under the bedplate.Allow 48 hours for the grout to harden.

8. Alignment. Alignment of the pump and motorthrough the flexible coupling is of extreme importancefor double-free mechanical operation. The followingsteps must be followed to establish the initial alignmentof the pumping unit:

(1) Tighten the foundation bolts.(2) Tighten the pump and motor holddown bolts.(3) Check the gap and angular adjustment as

discussed previously.

Figure 81. Checking angular alignment.

(4) Check parallel alignment by laying a straightedgeacross both coupling rims at the top, bottom, and bothsides, as shown figure 82. The unit will be in horizontalparallel alignment when the straightedge rests evenly onboth halves of the coupling at each side. In some specialservices a wide differential will prevail between theoperating temperatures the pump and motor. Adjustmentof alignment to satisfy such operating conditions must begoverned by the specific application. The verticaldifference of the shafts should be measured with astraightedge and feelers. To establish parallel alignment,thin shim stock is placed under the motor base.Occasionally, shims may be required under the pumpbase.

(5) Remember, alignment in one direction may alterthe alignment in another. Check through each alignmentprocedure after making an alignment alteration.

9. The unit should be checked periodically foralignment. If the unit does not stay in line

Figure 82. Checking parallel alignment.

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after being properly installed, the following are possiblecauses:

• Settling, seasoning, or springing of thefoundation

• Pipe strains distorting or shifting the pump• Shifting of the building structure• Spring of the baseplate

10. Piping. Connect the suction to the suctionopening in the pump casing. Be sure that all suctionconnections are airtight. Use a good pipe jointcompound on all threaded joints and airtight, packedunions. Suction piping smaller than the casing tappingmay be used if necessary. Larger size suction piping thanthe casing tapping is not recommended. A strainershould be installed in suction line to protect the pumpfrom foreign matter that may be present in the water.

11. The discharge piping is connected to thedischarge threaded opening. This opening is larger thanthe suction opening. Smaller size discharge ping may beused, but the will be a loss of head and capacity.

12. Both pipes must be properly supported so thatthere will not be a strain set up. The strain could causebreakage of the pump casing or misalignment.

13. Now that you have installed the pump you areready to check its operation. To check the operation, youmust know the operating characteristics of the pump.

27. Operation

1. This centrifugal pump may be used as a coolingor chilled water pump. Whichever application it serves,the method of operation remains the same. The pumpmust be filled through the priming opening before it isstarted. Prime the pump by removing the priming plugon top of the pump casing and filling the pump with theliquid to be pumped. Be sure that all the plugs in thepump casing are screwed in tightly. Rotate the pumpshaft by hand in the direction of the arrow on the casingto be sure that it moves freely. The pump is now readyto be started. Remember, after the pump is started, youmust check to insure that the direction of rotation agreeswith the arrow on the casing.

2. After the pump is up to speed, the priming timewill depend on the size and length of the suction line. Iffor any reason the pump is stopped during the primingperiod, be sure to check the liquid level in the pumpbefore restarting it.

3. If a newly installed pump fails to prime, youmust be sure that the following conditions exist:

(1) All the plugs on the pump casing are airtight.(2) The liquid level of the pump is at least to the

priming level.

(3) All suction line joints are airtight.(4) The motor direction matches the arrow on the

pump casing.(5) The motor reaches its rated nameplate speed.(6) Suction strainer is clean.

4. Insufficient pump discharge can be caused byimproper priming, air leaks in the suction line or pumpstuffing box, low motor speed, plugged impeller orsuction opening, wrong direction of rotation, wornstuffing box packing, and mechanical pump defects.These faults can also be related to low pump pressure andexcessive power consumption. Proper operation of thepump is the result of good maintenance policies.

28. Maintenance

1. If the internal components of the pump becomeworn, you should replace the entire pump with another ofthe same size to insure the same pumping capacity.After the new pump is installed, it must be aligned aspreviously discussed.

2. Stuffing Boxes. In repacking be sure thatsufficient packing is placed back of the lantern ring,shown in figure 83, so that the liquid for sealing isbrought in at the lantern ring and not at the packing.

3. The piping supplying the sealing liquid should betightly fitted so that no air enters. On suction lifts, asmall quantity of air entering the pump at this point mayresult in loss of suction. If the liquid being pumped isdirty, gritty, or acidic, the sealing liquid should be pipedto the stuffing box from a clean source of water. Thisprocedure will help prevent damage to the packing andshaft sleeve.

4. Packing should not be pressed too tight, sincethis may result in burning the packing and scoring theshaft sleeve. A stuffing box is not properly packed iffriction in the box is so great that the shaft cannot beturned by hand.

5. Always remove and replace all of the oldpacking. Do not reuse any of the old packing rings. Inplacing the new packing each packing ring should be cutto the proper length so that the ends come together butdo not overlap. The succeeding rings should be placed inthe stuffing box so that the joints of the rings arestaggered 180° apart for two-ring packing, 120° for three-ring, and so on.

6. If the pump is packed with metallic packing andstored for a great length of time, it may be necessary toapply leverage to free the rotor. When first starting thepump, the packing should be slightly loose, withoutcausing an air leak. If the gland leaks, put some heavy oilin the stuffing

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Figure 83. Cutaway of bearing and stuffing box.

box until the pump works properly. Then graduallytighten the gland.

7. When stuffing boxes are water sealed, you mustbe sure the water seal valves are opened sufficiently toallow a slight leakage of water. The leakage is piped awayto a sump or sewer. Many pump failures occur becausepersonnel observe liquid dripping from a gland andendeavor to stop it by tightening the gland bolts.Excessive tightening will cause the packing to burn andalso may score the shaft.

8. All general-service pumps are shipped with thehighest grade of soft, square asbestos packing,impregnated with oil and graphite.

9. Mechanical Seals. A mechanical seal is used inplace of a stuffing box. This seal requires no

adjustments, but it may be necessary to replace certainitems should they become scored or broken. Let usdiscuss dismantling and assembling the mechanical shaftseal assembly.

10. Dismantling. Back off the gland bolts to free thegland plates. Then remove the rotating element from thepump and take off the bearings and shaft nuts. Let usfollow the remaining steps as illustrated in figure 84.

11. Remove the floating seat and sealing washer.Do not disturb the bellows unless it needs replacement.The bellows becomes adhered to the sleeve if the seal hasbeen in use for any length of time and will be damaged ifmoved. If it requires replacement, it must be forced offthe sleeve. After the bellows is removed, the remainingparts-spring, spring holder, retainer shell, and drivingband-may be taken off. If the seal uses a set collar, youmust measure its location on the shaft before removing itso as to correctly relocate it during assembly.

12. Assembly. In assembling a mechanical seal,clean up all the parts and lightly oil the surface of thefloating seat and the shaft sleeve. Use light oil-notgrease.

13. Make sure that the synthetic rubber seat is tightagainst the shoulder of the floating seat with the roundedouter edge to the rear to facilitate insertion. Push thisassembly firmly into the cavity in the gland plate and seatit squarely. Do not push on the lapped face of thefloating seat.

14. The next step is to put the spring holder or setcollar in place. If a set collar is used you must locate thecollar in a position on the shaft determined by themeasurement taken during dismantling.

15. Place the remainder of the seal parts on theshaft as an assembly. When the extended length of theseal assembly is longer than the undercut portion of thesleeve or than the distance from the collar to the end ofthe sleeve, the spring must be compressed beforehandand tied

Figure 84. Cutaway of a mechanical seal.

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Figure 85. Flexible coupling.

together with string. The string should be removed afterinstallation and after partial tightening of the gland bolts.Be sure there are no burrs on the sleeve that would harmthe bellows. The new bellow is pushed straight on thesleeve.

16. The casing joint gasket should be cut at leastone-eighth of an inch oversized and trimmed after theupper half-casing is bolted down.

17. Bearings. The four types of bearings found incentrifugal pumps are grease-lubricated (1) ball and (2)roller bearings, (3) oil-lubricated sleeve bearing, and (4)oil-lubricated ball bearings. The importance of properlubrication cannot be overemphasized. The frequency oflubrication depends upon the conditions of operation.Overlubrication is the primary cause of overheatedbearings. For average operating conditions it isrecommended that grease be added at intervals of 3 to 6months.

18. The housing should be kept clean, for foreignmatter will cause the bearing to wear prematurely. Whenyou clean the bearing, use clean solvent and wipe it witha clean cloth. Do not use waste to wipe the bearingbecause it will leave lint.

19. A regular ball bearing grease must be used. Anumber 1 or 2 grease is satisfactory for most chill orcooling water pump applications. Mineral greases with asoda soap base are recommended. Greases made fromanimal or vegetable oil should not be used because of thedanger of deterioration and the formation of acid. Mostof the leading oil companies have special bearing greasesthat are satisfactory. For specific information of lubricantrecommendations you should consult the manufacturer’sservice bulletins.

20. The maximum operating temperature for ball

bearings is 180° F. If the temperature rises above 180°F., the pump should be shut down and the causedetermined.

21. The oil-lubricated ball bearing is filled with agood grade of filtered mineral oil (SAE 10) ofapproximately 150 Saybolt viscosity a 100° F. The oilshould be changed when it becomes dirty, and thebearing should be cleaned at the same time. The bearingshould be checked for wear frequently. Make sure thatthe oil rings are turning freely when the pump is firststarted. They are observed through the oil holes in thebearing caps.

22. The maximum operating temperature forbabbitted sleeve bearings is 150° F. If the bearingtemperature exceeds 150° F, shut down the pump untilthe cause is determined and corrected. Before the pumpis started, the bearing should be flushed thoroughly witha light grade of oil to remove any dirt or foreign matterthat may have accumulated during storage or installation.The bearing housing should then be filled to theindicated level with a good grade filtered mineral oil(SAE 10) of approximately 150 Saybolt viscosity at 100°F.

23. Couplings. We have already discussed the“spider insert” coupling. Another coupling you will comein contact with is the “Magic-Grip.”

24. The “Magic Grip” coupling, shown in figure 85,consists primarily of two cast iron discs and twobushings. The bushing is split, which allows it to slideeasily on the shaft. The outer diameter of the bushingand the inside diameter of the coupling are tapered.There a four drilled recesses in the bushing whichaccommodate the OFF and ON positions of the setscrewholes of the coupling. The recesses in the bushings areoffset so that when the setscrews are tightened thebushing will either draw in on the taper and

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tighten on the shaft or push out of the taper and loosenon the shaft.

25. The coupling is not intended to be a universaljoint. It is capable of taking care of minor angularmisalignment, but you must be sure to carefully align thecoupling during installation.

26. To install the coupling, slide the bushing on thepump or motor shaft with the recess holes away from thepump. Next place the coupling over the bushing. Insertboth setscrews in the ON position and tighten themalternately until the coupling is tight on the shaft.

27. To remove the coupling, remove both setscrewsfrom the ON position and insert them in the OFFposition. Turn the setscrews until the coupling is free onthe busing; then loosen the setscrews and remove thecoupling from the bushing. The bushing will now slideoff the shaft.

Review Exercises

The following exercises are study aids. Write youranswers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the test. Do not submit your answers for grading.

1. How many pounds of cement would you haveto mix with 12 pounds of sand and 24 poundsof crushed rock to form the concrete foundationfor a pump? (Sec. 26, Par. 1)

2. Why is a 1-inch space left between the concretefoundation and the baseplate? (Sec. 26, Par. 1)

3. How large a pipe sleeve would you use with abaseplate bolt measuring three-fourths of an inchin diameter? (Sec. 26, Par. 1)

4. Where do you place the wedges to level thebaseplate? (Sec. 26, Par. 3)

5. How do you check the angular alignment of a“spider” coupling? (Sec. 26, Par. 4)

6. How is angular alignment accomplished? (Sec.26, Par. 5)

7. Explain the procedure used to grout the pumpunit on the foundation. (Sec. 26, Par. 7)

8. How many parts of Portland cement to sharpsand are used to make grout? (Sec. 26, Par. 7)

9. How long should you allow the grout to harden?(Sec. 26, Par. 7)

10. Explain the steps you must follow to establishthe initial alignment of the pumping unit. (Sec.26, Par. 8)

11. Why would alignment be necessary after theunit has been operating for a period of time?(Sec. 26, Par. 9)

12. A _________________ is installed in thesuction line to protect the pump from foreignmatter. (Sec. 26, Par. 10)

13. What will occur if you install a smaller dischargepipe than the threaded discharge opening in thepump? (Sec. 26. Par. 11)

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14. How is the pump primed? (Sec. 27, Par. 1)

15. Explain what you should do after the pump isprimed and before it is stared. (Sec. 27, Par. 1)

16. List at least four causes for failure of a newlyinstalled pump to prime. (Sec. 27, Par. 3)

17. A pump that uses a stuffing box takes liquid infor sealing at ___________________. (Sec.28, Par. 2)

18. When is it necessary to pipe water from a cleanwater source to the stuffing box? (Sec. 28, Par.3)

19. Why is exact packing tightening important?(Sec. 28, Par. 4)

20. How would you stagger the packing joints in thestuffing box that uses five rings? (Sec. 28, Par.5)

21. The first step to perform when dismantling amechanical seal is to _________________.(Sec. 28, Par. 10)

22. Which item shouldn’t you disturb whendismantling a mechanical pump unless it is to bereplaced? (Sec. 28, Par. 11)

23. Name the four types of bearings commonlyfound in centrifugal pumps. (Sec. 28, Par. 17)

24. What occurs when a bearing is lubricated toooften? (Sec. 28, Par. 17)

25. What type of grease is recommended for grease-lubricated bearings? (Sec. 28, Par. 19)

26. Why aren’t vegetable and animal greases used tolubricate pump bearing? (Sec. 2, Par. 19)

27. The maximum operating temperature for grease-lubricated bearings is __________________.(Sec. 28, Par. 20)

28. The maximum operating temperature for an oil-lubricated babbitted sleeve bearing is___________________. (Sec. 28, Par. 22)

29. What are the four drilled recesses in the bushingof a “Magic-Grip” coupling used for? (Sec. 28,Par. 24)

30. (Agree)(Disagree) During installation of a“Magic-Grip” coupling, the recessed holes shouldbe facing the pump. (Sec. 28, Par. 26)

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CHAPTER 6

Fundamentals of Electronic Controls

A MISSILE STREAKS across the sky. The missile’sflight is controlled electronically from a command post.The success of the launch and flight of the “bird”depends largely upon how well the electronic techniciansperformed their tasks.

2. Let us compare the missile launch to anelectronic control system. The missile can be comparedto the controlled variable-humidity, temperature, airflow,etc. The movable rocket motor is the controlled device.The controlled device is the component within thesystem that receives a signal from the control tocompensate for a change in the variable. Last, but notleast, we have the guidance system. Our controllersthermostats, humidistats, etc. -perform in much the sameway as a guidance system. A change in the controlledvariable will cause the controller to respond with acorrective signal.

3. In this chapter we will discuss vacuum tubes,amplification, semiconductors, transistor circuits, bridgecircuits, and discriminator circuits. We will relateamplifier, bridge, and discriminator circuits to electroniccontrols. Electronic controls are becoming popular in theequipment cooling area of your career field because oftheir sensitivity and reaction time.

29. Vacuum Tubes

1. Electricity is based entirely upon the electrontheory--that an electron is a minute, negatively chargedparticle. Atoms consist of a positively charged nucleusaround which are grouped a number of electrons. Thephysical properties of any atom depend upon the numberof electrons and the size of the nucleus; however, almostall matter has free electrons. The movement of thesefree electrons is known as a current of electricity. If themovement of electrons is in “one” direction only, this isdirect current. If, however, the source of voltage isalternated between positive and negative, the movementof electrons will also alternate; this is alternating current.

2. The vacuum tube differs from other electricaldevices in that the electric current does not flow througha conductor. Instead, it passed through a vacuum insidethe tube. This flow of electrons is only possible if freeelectrons are somehow introduced into the vacuum.Electrons in the evacuated space will be attracted to apositively charged object within the same space becausethe electrons are negatively charged. Likewise, they willbe repelled by another negatively charged object withinthe same space. Any movement of electrons under theinfluence of attraction or repulsion of charged objects isthe current in a vacuum. The operation of all vacuumtubes depends upon an available supply of electrons.Electron emission can be accomplished by severalmethods--field, thermionic, photoelectric andbombardment-but the most important is thermionicemission.

3. Thermionic Emission. To get an idea of whatoccurs during thermionic emission you should visualizethe Christmas sparkler. When you light the sparkler itburns and sparks in all directions. The filament in avacuum tube reacts the same way when heated to a hightemperature. Millions of electrons leave the filament inall directions and fly off into the surrounding space. Thehigher the temperature, within limits, the greater thenumber of electrons emitted. The filament in a directlyheated vacuum tube is commonly referred to as acathode. Refer to figure 86 for the symbol of a filamentin a vacuum tube with heating sources.

4. The cathode must be heated to a hightemperature before electrons will be given off. Howeverthis does not mean that the heating current must flowthrough the actual material that does the emitting. Youcan see in figure 87 that the part that does the heatingcan be electrically separate from the emitting element. Acathode that is separate from the filament is an indirectlyheated cathode, whereas an emitting filament is a directlyheated cathode.

5. Much greater electron emission can be

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Figure 86. Thermionic emission.

obtained, at lower temperatures, by coating the cathodewith special compounds. One of these is thoriatedtungsten, or tungsten in which thorium is dissolved.However, much greater efficiency is achieved in theoxide-coated cathode, a cathode in which rare-earthoxides form a coating over a metal base. Usually thisrare-earth oxide coating consists of barium or strontiumoxide. Oxide-coated emitters have a long life and greatemission efficiency.

6. The electrons emitted by the cathode stay in itsimmediate vicinity. These form a negatively chargedcloud about the cathode. This cloud, which is called aspace charge, will repel those electrons nearest thecathode and force them back in on it. In order to use

these electrons, we must put a second element within thevacuum tube. This second element is called an anode (orplate), and it gives us our simplest type of vacuum tube,the diode.

7. Diode Vacuum Tube. Each vacuum tube musthave at least two elements or electrodes: a cathode andan anode (commonly called a plate). The cathode is anemitter of electrons and the plate is a collector ofelectrons. Both elements are inclosed inside an envelopeof glass or metal. This discussion centers around thevacuum tube diode from which the air as much possiblehas been removed. However, it should be understoodthat gaseous diodes do exist. The

Figure 87. Indirectly and directly heated cathodes.

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Figure 88. Electron flow in a diode.

term “diode” refers to the number of elements within thetube envelope (di meaning two) rather than to anyspecific application, as shown in figure 88.

8. The operation of the diode depends upon thefact that if a positive voltage is applied to the plate withrespect to the heated cathode, current will flow throughthe tube. When the plate is negative with respect to thecathode, current will not flow through the tube. Sincecurrent will pass through a vacuum tube in only onedirection, a diode can be used to change a.c. to d.c.

9. Diode as a half-wave rectifier. Experiments withdiode vacuum tubes reveal that the amount of currentwhich flows from cathode to plate depends upon twofactors: the temperature of the cathode, and the potential(voltage) between the cathode and the plate. Refer to

figure 89, a diagram of a simple diode rectifier circuit.10. When an a.c. source is connected to the plate

and cathode such a circuit, one-half of each a.c. cycle willbe positive and the other half will be negative.Therefore, alternating voltage from the secondary of thetransformer is applied to the diode tube in series with aload resistor, R. The voltage varies, as is usual with a.c.,but current passes through the tube and R only when theplate is positive with respect to the cathode. In otherwords, current flows only during the half-cycle when theplate end of the transformer winding is positive. Whenthe plate is negative, no current will pass.

11. Since the current through the diode flows in onedirection only, it is direct current. This type of dioderectifier circuit is called a half-

Figure 89. Simple half-wave rectifier circuit.

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Figure 90. Output of a half-wave rectifier.

wave rectifier, because it rectifies only during one-half ofthe a.c. cycle. As a result, the rectified output will bepulses of d.c., as shown in figure 90. You can see fromfigure 90 that these pulses of direct current are quitedifferent from pure direct current. It rises from zero to amaximum and returns to zero during the positive half-cycle of the alternating current, but does not flow at allduring the negative half-cycle. This type of current isreferred to as pulsating direct current to distinguish itfrom pure direct current.

12. In order to change this rectified alternatingcurrent into almost pure direct current, these fluctuationsmust be removed. In other words, it is necessary to cutoff the humps at the tops of the half-cycles of currentand

fill in the gaps caused by the negative half-cycle of nocurrent. This process is called “filtering” ‘

13. Look at the complete electrical circuit of figure91. Filtering is accomplished by connecting capacitors,choke coils (inductors), and resistors in the propermanner. If a filter circuit is added to the half-waverectifier, a satisfactory degree of filtering can be obtained.Capacitors C1 and C2 have a small reactance at the a.c.frequency, and they are connected across the loadresistor, R. These capacitors will become charged duringthe positive half-cycles as voltage is applied across theload resistor. The capacitors will discharge through Rand L during the negative half-cycles, when the tube isnot conducting, thus tending to smooth out, or filter out,the

Figure 91. Filter network added to a half-wave rectifier.

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Figure 92. Full-wave rectifier.

pulsating direct current. Such a capacitor is known as afilter capacitor.

14. Inductor L is a filter choke having highreactance at the a.c. frequency and a low value of d.c.resistance. It will oppose any current variations, but willallow direct current to flow almost unhindered throughthe circuit. In order use both alternations of a.c., thiscircuit must be converted to a full-wave rectifier.

15. Diode used or full-wave rectification. Onedisadvantage of the half-wave rectifier is that no currentis available from the transformer during the negativehalf-cycle. Therefore, some of the voltage producedduring the positive half cycle must be used to filter outthe voltage variations. This filtering action reduces theaverage voltage output of the circuit. Since the circuit isconducting only half the time, it is not very efficient.Consequently, the full-wave rectifier, which rectifies bothhalf-cycles, was developed for use in the power supplycircuits of modern electronic equipment.

16. In a full-wave rectifier circuit, two diodes maybe used. However, in many applications, the two diodesare included in one envelope and the tube is referred toas a duo-diode. A typical example of a full-wave rectifiercircuit is shown in figure 92. In this circuit a duo-diodeis used, and the transformer’s secondary winding has acenter tap. Notice that the center tap current is turned toground and then through R and inductor L to thecathode (filament) of V1. The voltage appearing acrossX and Y is 700 volts a.c. The center tap is at zeropotential with 350 volts on each side.

17. Point X of the high-voltage winding isconnected to plate P2, and Y is connected to P1. Theplates conduct

alternately, since at any given instant, one plate is positiveand the other is negative. During one half-cycle, P1 willbe positive with respect to the center tap of thetransformer secondary winding while P2 will be negative.This means that P1 will be conducting while P2 isnonconducting.

18. During the other half-cycle, P1, will be negativeand nonconducting while P2 will be positive andconducting. Therefore, since the two plates take turns intheir operation, one plate is always conducting. Currentflows through the load resistor in the same directionduring both halves of the cycle, which is called full-waverectification. The circuit shown in figure 92 is the basisfor all a.c. operated power supplies that furnish d.c.voltages for electronic equipment. Notice that the heatervoltage for the duo-diode is taken from a specialsecondary winding on the transformer.

19. The next tube you will study is the triode. Thetriode is used to amplify a signal.

30. Amplification

1. With the invention of the triode vacuum tube,the amplification of electrical power was introduced.Technically speaking, amplification means slaving a larged.c. voltage to a small varying signal voltage to make thelarge d.c. voltage have the same wave shape as the signalvoltage. As a result, the wave-shaped d.c. voltage will dothe same kind of work as the signal voltage will do, butin a larger quantity. After the triode came the tetrode,pentode, etc., to do a much better job of amplificationthan the triode. Amplification by use of the triode andother multi-element

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vacuum tubes will be discussed in this section.2. Triode Vacuum Tube. In the diode tubes

previously described, current in the plate circuit wasdetermined by cathode temperature and by the voltageapplied to the plate. A much more sensitive control ofthe plate current can be achieved by the use of a thirdelectrode in the tube. The third electrode (or element),called a control grid, is usually made in the form of aspiral or screen of fine wire. It is physically locatedbetween the cathode and plate, and is in a separateelectrical circuit. The term “grid” comes from its earlyphysical form.

3. The control grid is placed much closer to thecathode than to the plate, in order to have a greatereffect on the electrons that pass from the cathode to theplate. Because of its strategic location the grid cancontrol plate current by variations in its voltage. Theoperation of a triode vacuum tube is explained in thefollowing paragraphs.

4. If a small negative voltage (with respect to thecathode) is applied to the grid, there is a change inelectron flow within the tube. Since the electrons arenegative charges of electricity, the negative voltage on thegrid will tend to repel the electrons emitted by thecathode, which tends to prevent them from passingthrough the grid on their way to the plate. However, theplate is highly positive with respect to the cathode andattracts many of the electrons through the grid. Thus,many electrons pass through the negative grid and reachthe plate in spite of the opposition offered them by thenegative grid voltage.

5. A small negative voltage on the grid of thevacuum tube will reduce the electron flow from thecathode to the plate. As the grid is made more and morenegative, it repels the electrons from the cathode, andthis in turn decreases plate current. When the grid biasreaches a certain negative value, the positive voltage onthe plate is unable to attract any more electrons and theplate current decreases to zero. The point at which thisnegative voltage stops all plate current is referred to ascutoff bias for that particular tube.

6. Also, as the grid becomes less and less negative,the positive plate attracts more electrons and currentincreases. However, a point is reached where platecurrent does not increase even though the grid bias ismade more positive. This point, which varies withdifferent types of tubes, is called the saturation level ofvacuum tubes. So you can see that the control grid actsas a valve controlling plate current. One other thingmust be made clear at this point. If the positive platevoltage is

increased, the negative grid voltage must be increased ifyou need to limit current through the tube.

7. Control Grid Bias. Grid bias has been definedas the d.c. voltage (potential) on the grid with respect tothe cathode. It is usually a negative voltage, but in somecases the grid is operated at a positive potential.Generally when the term “bias” is used, it is assumed tobe negative. There are three general methods ofproviding this bias voltage.

8. The first is fixed bias. Figure 93 shows how thenegative terminal of a battery could be connected to thecontrol grid of a tube, and the cathode connected toground to provide bias. If you say that the bias is 5 volts,you mean that the grid is 5 volts “negative” with respectto the cathode. Two methods of obtaining a bias of 5volts are shown in figure 93. In diagram X the battery isconnected with its negative terminal to the grid, while itspositive terminal and the cathode are grounded. DiagramY shows the positive terminal of the battery connected tothe cathode, while its negative terminal and the grid aregrounded. In either case, the grid is 5 volts negative withrespect to the cathode. If the grid and the cathode are atthe same potential, there is no difference in voltage andthe tube is operating at zero bias (diagram Z).

9. The second method of obtaining grid bias iscalled cathode bias. The cathode bias method uses aresistor (Rk) connected in series with the cathode, asshown in figure 94. As the tube conducts, current is insuch a direction that the end of the resistor nearest thecathode is positive. The voltage drop across Rk makesthe grid negative with respect to the cathode. Thisnegative grid bias is obtained from the steady d.c. acrossRk. The amount of grid bias on the triode tube isdetermined by the voltage drop (IR) across Rk.

10. Any signal that is fed into the grid will changethe amount of current through the tube, which in turnwill change the grid bias, due to the fact that current alsochanges through the cathode resistor. To stabilize thisbias voltage, the cathode resistor is bypassed by acondenser, C1, that has low resistance compared with theresistance of Rk. Here’s how this works.

11. As the triode conducts, condenser C1, willcharge. If the tube, due to an input signal, tends toconduct less, C1, will discharge slightly across RR, andkeep the voltage drop constant. The voltage drop acrossthe cathode resistor is held almost constant, even thoughthe signal is continually varying.

12. Our third method of getting grid bias is calledcontact potential, or grid-leak bias. This type of biasdepends upon the input signal. Two circuits usingcontact potential or grid-leak bias,

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Figure 93. Using a battery to get fixed or zero bias.

are shown figure 95. The action in each case is similar-that is, when an a.c. signal is applied to the grid, it drawscurrent on the positive half-cycle. This current flows inthe external circuit between the cathode and the grid.This current flow will charge condenser C1, as shown bythe dark, heavy lines. One thing to keep in mind at thistime is the ohmic value of the grid resistor. It is veryhigh, in the order of several hundred thousand ohms.

13. As the signal voltage goes through the negativehalf-cycle, the condenser C1, starts discharging. The

control grid cannot discharge through the tube since it isnot an emitter of electrons. The only place to can startdischarging is through the grid resistor, Rg,. Thisdischarge path is flown by the dotted arrows. A negativevoltage is developed across Rg, which biases the tube.Since the resistor, Rg, has a very high value (500,000ohms to several megohms), the condenser only has timeto discharge a small amount before a new cycle begins.This means that only a very small current flows, or leaksthrough. However, because of the large value of Rg, C1

Figure 94. Cathode biasing with a cathode resistor.

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Figure 95. Connect potential bias.

will remain continuously charged to some value as longas a signal is applied.

14. One of the main disadvantages of this type ofbias is the fact that bias is developed only when a signalis applied to the grid. If the signal is removed for anyreason, the tube conducts very heavily and may bedamaged. This condition can be prevented by using“combination bias,” which uses both grid-leak bias andcathode bias. This combination provides the advantagesneeded with an added safety precaution in case the signalis removed.

15. Triode Tube Operation. Since a small voltagechange on the grid causes a large change in plate current,the triode tube can be used as an amplifier. If a smalla.c. voltage is applied between the cathode and the grid,it will cause a change in grid bias and thus vary platecurrent. This small a.c. voltage between cathode and gridis called a signal.

16. The large variations in plate current through theplate load resistor (RL) develops an a.c. voltagecomponent across the resistor which is many times largerthan the signal voltage. This process is calledamplification and is illustrated in figure 96.

17. The one tube and its associated circuits (theinput and output circuits) is called one stage ofamplification or a one-stage amplifier. A single-stageamplifier might not produce enough amplification or gainto do a particular job. To increase the overall gain, theoutput of one stage

may be coupled to the control grid of another stage andthe output amplified again. Look at figure 97 for a two-stage amplifier. There are various types of couplings.But generally the idea is to block the d.c. plate voltage ofthe preceding stage to keep it off the grid of thefollowing stage because it would upset the bias of thefollowing stage. A capacitor is used to couple one stageto another because a capacitor blocks d.c. or will not let itpass.

18. Tetrode Amplifiers. While a triode is a goodamplifier at low frequencies, it has a fault when used incircuits having a high frequency. This fault results fromthe capacitance effect between the electrodes of the tubeand is known as interelectrode capacitance. Thecapacitance which causes the most trouble is between theplate and the control grid. This capacitance couples theoutput circuit to the input circuit of the amplifier stage,which causes instability and unsatisfactory operation.

19. To correct this fault, another tube was built thathas a grid similar to the control grid placed between theplate and the control grid as seen in figure 98. This newgrid is connected to a positive potential somewhat lowerthan the plate potential. It is also connected to thecathode through a capacitor. The second grid serves as ascreen between the plate and the control grid and iscalled a screen grid. The tube is called a tetrode.

20. Beam Power Tubes. Electron tubes whichhandle large amounts of current are known as beampower amplifiers. Let us compare a voltage

110

Figure 96. Triode tube operation.

amplifier with a power amplifier. A voltage amplifiermay draw 10 milliamperes of plate current while a poweramplifier can draw 250 milliamperes of plate current.The beam power amplifier is more rugged, with largerelements, and must dissipate heat faster due to thegreater current.

21. In figure 99 a specially constructed tetrodewhich has a filament or cathode, control grid, screen grid,and plate is called a beam power tetrode. To eliminate

secondary emission effect, the screen grid wires lie in theshadow of the control grid thus forming the spacecurrent into narrow beams. The resulting beams providethe effect of suppressor grid action, and thus permits thecharacteristic curves to be similar to those of a pentode.

22. Because of the amount of electrons in thenegatively charged beam, any secondary electrons emittedby the plate are returned to the plate. By internallyconnecting the beam-forming plates to the cathode, theconcentration of the electrons are

Figure 9. Two-stage amplifier.

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Figure 98. Tetrode amplifier circuit.

even higher, causing the beam to act as a suppressor gridin the pentode.

23. Pentode Amplifiers. The tetrode tube is abetter amplifier than the triode tube, but it also has afault. A cold plate does not normally emit electrons.However, high-velocity electrons, produced by thepositive potential on the screen grid, cause other electronsto be knocked from the plate. The liberation of theseelectrons is called secondary emission. The secondaryelectrons will be attracted to the positive screen grid andwill reduce the plate current. To overcome this, avacuum tube was designed that contains still another grid.This grid, shown in figure 100, is called a suppressor gridand is placed between the plate and the screen grid. Anegative potential is applied to the suppressor grid, andthe negative potential forces the secondary electrons backto the plate and prevents secondary electrons fromreaching the screen grid. These five-element tubes, orpentodes, are the highest development of amplifier tubes.

24. Classes of Amplifiers. Amplifiers are dividedinto the following classes, based on tube operation or biasvoltage:

Figure 99. Construction of a beam-power tube.

• A class A amplifier has plate current or conductsfor 360° of the input signal.

• A class B amplifier conducts for 180° of theinput signal.

• A class AB amplifier is a combination of bothclass A and B.

• A class C amplifier has plate current flowing forapproximately 120° of the input signal.

25. Vacuum tubes have several disadvantages -size,warming up period, etc. Transistors are rapidly replacingvacuum tubes in electronic controls. To understandtransistors, you must have a good knowledge ofsemiconductors.

31. Semiconductors

1. The transistor was discovered in 1948 by theBell Laboratories. The name comes from two words,“transfer” and “resistance.” The transistor is graduallyreplacing the vacuum tube and is playing a big part in thedesign of all types of electronic equipment. The mainadvantages

Figure 100. Pentrode amplifier tube.

112

Figure 101. Elements associated with transistors.

of the transistor over the vacuum tube are that it smaller,lighter, and more rugged, and operates at lower voltagesthan the vacuum tube.

2. Atomic Structure. Essential to theunderstanding of semiconductor operation is the study ofatomic characteristics and the basic structure of the atom.The atom contains a nucleus composed of protons andneutrons. Protons are positively charged particles, whileneutrons are neutral particles.

3. The other component of the atom is theelectron, which is a negatively charged particle. Theelectrons are arranged in orbits around the nucleus. Theorbits, or rings, are numbered starting with the ringnearest the nucleus (which is No. 1) and progressingoutward.

4. The maximum number of electrons permitted ineach ring is as follows: Ring No. 1, 2 electrons; ring No.2, 8 electrons; ring No. 3, 18 electrons; ring No. 4, 32electrons. The atomic structure of germanium andsilicon have 14 and 32 electrons respectively. The 3d ringin silicon and the 4th ring in germanium are incomplete,having only 4 electrons. These incomplete outer rings areimportant to the operation of semiconductor devices. Agood conductor has less than 4 electrons in its outer ring.A good insulator has more than 4 electrons in its outerring. A good semiconductor has 4 electrons in its outer

Figure 102. Structure of atoms.

Figure 103. Atoms of semiconductors.

ring. Another name for the outer ring or orbit is thevalence ring. The helium atom and the hydrogen atomare both good conductors of electricity--the hydrogenatom being the better.

5. Atomic Number. Atoms of different elementsare found to have a different number of protons andneutrons in their nucleus. The atomic numbers of someof the elements are listed in figure 101. Figure 102shows the structure of a hydrogen atom and a heliumatom, two examples of good conductors. Figure 103shows the structure of a germanium atom and a siliconatom, which are examples of a semiconductor.

6. An atom that has only four electrons in its outerorbit or ring will combine with other atoms whose outerorbits are incomplete. If a number of germanium atomsare joined together into crystalline form, the process iscalled covalent bonding of germanium atoms. Figure 104shows germanium atoms in covalent bonding. Figure 105illustrates an atom of germanium and an atom ofantimony. For simplification, only the nucleus and theouter rings are shown for each atom. The outer orvalence ring for the germanium atom contains fourelectrons, while

Figure 104. Crystalline germanium.

113

Figure 105. Typical atoms.

the valence ring for the antimony atom contains fiveatoms.

7. If a small amount of antimony is added tocrystalline germanium, the antimony atoms will distributethemselves throughout the structure of the germaniumcrystal.

8. Figure 106 shows that an antimony atom hasgone into covalent bonding with germanium. Theantimony atom in the material donates a free electronand these free electrons will support current flow throughthe material. The antimony is called a donor in that itdonates free electrons. The germanium crystal nowbecomes an N-type (negative type) germanium.

9. P-type (positive type) germanium can beprepared by combining germanium and indium atoms.Figure 107 shows germanium and indium in covalentbonding. For every indium atom in the material, therewill be a shortage of one electron that is needed tocomplete covalent bonding between the two elements.This shortage of an electron can be defined as a hole.This type of material will readily accept an electron tocomplete

Figure 106. N-type germanium.

Figure 107. P-type germanium.

its covalent bonding and is therefore called acceptor typematerial.

10. The hole can be looked upon as a positive typeof current carrier, as compared to the electron which is anegative type current carrier. The hole can be movedfrom atom to atom the same as the electron can bemoved from atom to atom. The hole moves in onedirection and the electron moves in the oppositedirection.

11. P-N Junctions. When N-type and P-typegermanium are combined in a single crystal, an unusualbut very important phenomenon occurs at the surfacewhere contact is made between the two types ofgermanium. The contact surface is referred to as a P-Njunction, shown in figure 108.

12. There will be a tendency for the electrons togather at the junction in the N-type material and likewisean attraction for the holes gather at the junction of theP-type material. These current carriers will notcompletely neutralize themselves because movement ofelectrons and holes cause negative and positive ions to beproduced, which means an electric field is set up in eachtype material that will tend to obstruct the movement ofcurrent carriers through the junction. This obstructionbuilds up a barrier that is referred to as a high resistanceor potential hill. This electric field may be referred to asa potential hill battery since the two materials haveacquired a polarity which opposes the normal movementof the current carries.

13. Reverse Bias. Figure 109 shows an externalvoltage applied to an N-P junction. The positiveelectrode of the battery is connected to the N-typematerial and the negative electrode is connected to the P-type material. Since the N-type material has an excess ofelectrons, the positive voltage being applied to thismaterial will

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Figure 108. P-N junction.

attract these electrons toward that end of the germaniumcrystal. The negative voltage being applied to the P-typematerial, which has an excess of positive current-carryingholes, will attract these holes toward the other end of thecrystal and away from the junction. The ammeter infigure 109 indicates no current flow. There is nopossibility of recombination at the junction because thepotential hill has been built up to a higher value by theapplication of an external voltage. This is called reversedbias condition or a high-resistance circuit.

14. Forward Bias. The battery can be connectedwith the opposite polarity and cause a different condition.In figure 110 the battery has been reversed, and now thenegative electrode of the battery is connected to the N-type material. This negative voltage will repel theelectrons in the N-type material toward the junction.The positive electrode is connected to the P-type materialwhich will repel the positive holes toward the junction.With this connection, recombination takes place at the

Figure 109. N-P junction with reverse bias.

junction, resulting in current toward the N-P junction.This method of connecting the battery is known asforward bias since it encourages current flow.

15. Diode Action. Combining P- and N-typegermanium into a single crystal is the basis of both diodeand transistor action. The P-N junction can be used as arectifier because of its ability pass current in one directionand practically no current in the other. Applying an a.c.voltage to this junction results in a d.c. output similar tothat produced by a vacuum tube diode. Figure 111 showsa semiconductor diode rectifying an alternating voltage.When this P-N junction is biased in the forwarddirection, current will flow across the load resistor, RL.When the junction is biased in the reverse direction, nocurrent will flow across the load resistor, RL. Forwardand reverse biasing is caused by the a.c. input.

16. Point-Contact Diode. Another type diode isthe point-contact diode, shown in figure 112.

Figure 110. P-N junction with forward bias.

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Figure 111. Half-wave rectification.

This diode operates similarly to the P-N junction type. Itconsists of a semiconductor (N-type germanium), a metalbase, and a metallic point contact (cat whisker). A fineberyllium-copper or phosphor-bronze wire is pressedagainst the N-type germanium crystal. During theconstruction of the diode a relatively high current ispassed through the metallic point contact into the N-typecrystal. This high current causes a small P-type area tobe formed around the point contact. Thus, a P-type andan N-type germanium are formed in the same crystal.The operation of this diode is similar to the P-N junctiondiode.

17. Transistor Triodes. A review of the operationof P-N germanium junctions reveals that a P-N junctionbiased in the forward direction is equivalent to the low-resistance element (high current for a given voltage).The P-N junction biased in the reverse direction isequivalent to a high-resistance element (low current for agiven voltage). For a given current, the power developedin a high-resistance element is greater than thatdeveloped in a low-resistance element. (Power is equal tothe current squared multiplied by the resistance value, orsimply: P = I2R.) If a crystal containing two P-Njunctions were prepared, a signal could be introduced intoone P-N junction biased the forward direction (lowresistance) and extracted from the other P-N junctionbiased in the reverse direction (high resistance). Thisbiasing produces a power gain of the signal whendeveloped in the external circuit. Such a device wouldtransfer the signal current from a low-resistance circuit toa high-resistance circuit.

18. P-N-P and N-P-N Junction Transistors. TheP-N-P transistor is constructed by placing a narrow stripof N-type germanium between two relatively long stripsof P-type germanium. And, as the letters indicate, the N-P-N transistor consists of a narrow strip of P-typegermanium between two relatively long strips of N-typegermanium.

19. To form two P-N junctions, three sections ofgermanium are required. Figure 113 shows the threesections separated. When the three sections arecombined a P-N-P transistor is formed, and each section,like each element in a vacuum tube, has a specific name:emitter, base, and collector. The base is located betweenthe emitter and collector, as the grid in a triode vacuumtube is located between the plate and cathode.

20. Note that when the three sections are combined,two space charge regions (barriers) occur at the junctioneven though there is no application of external voltages,or fields. This phenomenon is the same as that whichoccurs when two sections are combined so as to form aP-N junction diode.

21. Transistor action requires that one junction bebiased in the forward direction and the second junction bebiased in the reverse direction. Figure 114 shows the firstjunction biased in the forward direction. The secondjunction is not biased. Note that the space charge region(barrier) at the first junction is considerably reduced whilethe space charge region at the second junction isunchanged. The condition is identical to that of a P-Njunction diode with forward bias.

22. Figure 114 shows the second junction biased inthe reverse direction. The first junction is not biased.Note that the space charge region (barrier) at the secondjunction increases. Except for minority carriers (notshown), no current flows across the junction. Thisphenomenon is the same as that which occurs when twosections are combined to form a P-N junction diode withreverse bias.

23. Figure 115 shows what happens when junctionsare biased simultaneously. Because of the simultaneousbiasing, a large number of holes from the emitter do notcombine with the electrons entering the base from theemitter-base battery. Many of the holes diffuse throughthe base and penetrate the base-collector space charge

Figure 112. Physical construction of a point-contact diode.

116

Figure 113. Two sections of P-type germanium and one section of N-type germanium.

region. In the collector region the holes combine withelectrons that enter the collector from the negativeterminal of the base-collector battery. If holes that enterthe base from the emitter-base junction avoidcombination with electrons entering the base from thebattery, the holes are attracted to the collector by theacceptor atoms (negative) in the collector and thenegative potential of the base collector battery.

24. To obtain maximum power gain in a transistor,most of the holes from the emitter must diffuse throughthe base region into the collector region. This conditionobtained in practice by making the base region verynarrow compared the emitter and the collector regions.In practical transistors, approximately 95 percent of thecurrent from the emitter reaches the collector.

25. By using forward bias on the emitter-to-basejunction there is a relatively low resistance, whereas byusing reverse bias on the collector-to-base junction thereis a relatively high resistance. A typical value for theemitter-to-base resistance is around 500 ohms, andaround

500,000 ohms for the collector-to-base resistance. ByOhms law, voltage is equal to current times resistance;thus, numerically stated:

26. Although the current gain (95 percent) in thisparticular transistor circuit is actually a loss, the ratio ofresistance from emitter to collector more than makes upfor this loss. Also, this same resistance ratio provides apower gain which makes the transistor adaptable to manyelectron circuits.

27. N-P-N Junction Transistors. The theory ofoperation of the N-P-N is similar to that of the P-N-Ptransistor. However, inspection and comparison offigures 115 and 116 will reveal two important differences:

• The emitter-to-collector carrier in the P-N-Ptransistor is the hole. The emitter-to-collector carrier inthe N-P-N transistor is the electron.

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Figure 114. Forward bias between emitter and base (A) and reverse bias between base and collector (B)

• The bias voltage polarities are reversed. Thiscondition is necessitated by the different positionalrelationships of the two types of germanium as used inthe two types of transistors.

28. Transistors and Electron Tubes. Some of thedifferences and similarities between electron tubes andtransistors are discussed in the following paragraphs.

29. The main current flow in an electron tube isfrom cathode to plate (shown in fig. 117). In a junctiontransistor, the main current flow is from emitter tocollector. The electron current in the electron tubepasses through a grid. In the transistor, the electroncurrent

passes through the base. The cathode, grid, and plate ofthe electron tube are comparable to the emitter, base, andcollector, respectively, of the transistor. Plate current isdetermined mainly by grid to cathode voltage, andcollector current is determined mainly by emitter-basevoltage. The electron tube requires heater current to boilelectrons from the cathode. The transistor has no heater.

30. For electron current flow in an electron tube,the plate is always positive with respect to the cathode.For current flow in a transistor, the collector may bepositive or negative with respect to the emitter dependingon whether the electrons or holes, respectively, are theemit-ter-to-collector carriers. For most electron tube

118

Figure 115. Simultaneous application of forward bias between emitter and base and reversebias between base and collector of P-N-P transistor.

applications, grid cathode current does not flow. Formost transistor applications, current flows betweenemitter and base. Thus, in these cases, the inputimpedance of an electron tube is much higher than itsoutput impedance and similarly the input impedance of atransistor is much lower than its output impedance.

31. Transistor Triode Symbols. Figure 118 showsthe symbols used for transistor triodes. In the P-N-Ptransistor, the emitter-to-collector current carrier in thecrystal is the hole. For holes to flow internally fromemitter to collector, the collector must be negative withrespect to the emitter. In the external circuit, electronsflow from emitter (opposite to direction of the emitterarrow) to collector.

32. In the N-P-N transistor, the emitter-to-collector

current carrier in the crystal is the electron. For electronsto flow internally from emitter to collector, the collectormust be positive with respect the emitter. In the externalcircuit, the electrons flow from the collector to theemitter (opposite to the direction of the emitter arrow).

33. Point-Contact Transistor. The point-contacttransistor is similar to the point-contact diode except fora second metallic conductor (cat whisker). These catwhiskers are mounted relatively close together on thesurface of a germanium crystal (either P- or N-type). Asmall area of P- or N-type is formed around these contactpoints. These two contacts are the emitter and collector.The base will be the N- or P-type of which the crystalwas formed. The operation of the point-contacttransistor is similar to the operation of the junction type.Now that you

Figure 116. Simultaneous application of forward bias between emitter and base andreverse bias between base and collector of N-P-N transistor.

119

Figure 117. Structure of a triode vacuum tube and a junction transistor.

have studied transistors you must know how they areconnected into the circuit.

32. Transistor Circuits

1. The circuit types in which transistors may beused are almost unlimited. However, regardless of thecircuit variations, the transistor will be connected by oneof three basic methods. These are: common base,common emitter, and common collector. Theseconnections correspond to the grounded grid, groundedcathode, and grounded plate respectively.

2. Common Base Circuit. Figure 119 shows acommon base circuit using a triode transistor. A thinlayer of P-type material is sandwiched between twopellets of N-type material. The layer of P-type material isthe base when the two pellets of N-type material are thecollector and the emitter. The emitter is connected tothe base through a small battery (B1). This battery isconnected with its negative electrode to the N-typeemitter and its positive electrode to the P-type base.Thus, the emitter-base junction has forward bias on it.Recombination of the electrons and holes causes base

current (Ib) to flow.3. Battery B2 is connected to produce reverse bias

on the collector-base junction. However, current willflow in the collector-base circuit. Let’s see why thiscurrent will flow. In this emitter, electrons move towardthe emitter-base junction due to the forward bias on thatjunction. Many of the electrons pass through theemitter-base junction into the base material. At thispoint the electrons are under the influence of the strongfield produced by B2. Since the base material is very thin,the electrons are accelerated into the collector. Thisresults in collector current (Ic), as shown in figure 119.About 95 percent of the electrons passing through theemitter-base junction enter the collector circuit. Thus,the base current (Ib), which is a result of recombinationof electrons and holes, is only 5 percent of the emittercurrent.

4. Common Emitter Circuit. The circuit that willbe encountered most often is the common emitter circuitshown in figure 120. Notice that the base is returned tothe emitter and the collector is also returned the emitter.The base-emitter circuit is biased by a small batterywhose negative electrode is connected to the N-type baseand

Figure 118. Transistor symbols.

120

Figure 119. Common base circuit.

The positive electrode to the P-type emitter. Thisforward bias results in a base-emitter current of 1milliampere. In the collector circuit the battery is placedso as to put reverse bias on the collector-base junction.The collector current (Ic) is 20 milliamperes. Since theinput is across the base emitter and the output is acrossthe collector emitter, there is a current gain of 20. Thepositive voltage on the emitter repels its positive holestoward the base region. Because of their high velocity,and because of the strong negative field of the collector,the holes will pass right on through the base material andenter the collector. Only 5 percent or less of thosecarriers leaving the emitter will enter through the circuit.The other 95 percent or more will enter the collector andconstitute collector current (Ic).

5. Common Collector Circuit. The commoncollector circuit in figure 121 operates in much the samemanner as a cathode follower vacuum tube circuit. It hasa high impedance and a low output impedance. It has asmall

power gain but no voltage gain in the circuit. The circuitis well suited for input and interstage couplingarrangements.

6. Transistor Amplifiers. Let’s put a signal voltageinto the circuit of figure 122 and trace the electron flow.A coupling capacitor (C1) is used to couple the signal intothe emitter-base circuit. Rg provides the right amount offorward bias. When the signal voltage rises in a positivedirection, the emitter will be made less negative withrespect to the base. This difference will result in areduction of the forward bias on the emitter-base circuitand, therefore, a reduction in current flow through theemitter. Since the emitter current is reduced, thecollector current will likewise be reduced at the sameproportion. As the signal voltage starts increasing in anegative direction, the emitter will now become morenegative with respect to the base, resulting in increasedforward bias. Increased forward bias

Figure 120. Common emitter circuit.

121

Figure 121. Common collector circuit.

Figure 122. Common base amplifier.

will result in increased current flow in the emitter andcollector circuits.

7. The signal being applied to the emitter-basecircuit has now been reproduced in the collector circuit.The signal has been greatly amplified because the currentflowing in the collector circuit is through a highimpedance network. It is also possible to use a P-N-Ptype transistor, as shown in figure 123.

8. The electrical resistance of a semiconductorjunction may vary considerably with its temperature. Forthis reason, the performance of a circuit will vary withthe temperature unless the circuit is compensated fortemperature variations. Compensating for temperatureminimizes the effects of temperature on operating biascurrents and will stabilize the d.c. operating conditions ofthe transistor. Now let us talk about the circuit thatfeeds the signal to the amplifier circuit-the bridge circuit.

33. Bridge Circuits

1. The brain of most electronic controls is amodified Wheatstone bridge. To understand the bridgecircuit will review the operation of a variable resistor(potentiometer) first. One of the principal uses of thepotentiometer is to take a voltage from one circuit to usein another. Figure 124 shows a potentiometer connectedacross a power source. The full 24 volts of the source isdropped between the two ends of the resistor; this meansthat 12 volts are being

Figure 123. Common emitter amplifier.

122

Figure 124. Potentiometer.

dropped across each half, or 6 volts across each quarter(1/4). If a voltmeter is connected from one end, and tothe movable wiper, it will read the voltage drop betweenthat end and the wiper. Note that meter A is reading thevoltage drop across ¼ of the resistance, or 6 volts.Meter B is reading the voltage drop across the remaining¾ of the resistance, or 18 volts. As the wiper is movedclockwise, the voltage shown on meter A will increaseand B will decrease. Later you will hear the word “pot.”This is short for potentiometer.

2. Figure 125 shows two resistances connected inparallel with their wipers connected to a voltmeter. Since

the two resistances are connected in parallel, the voltageapplied by the battery is equally distributed along each ofthe two “pots.” Such a combination of “pots” is called abridge. Notice that each wiper is at a positive potentialwith respect to point C of 6 volts, and consequently thevoltmeter indication is zero volts. Since no current flowsbetween the wipers, the bridge is said to be balanced. Ifwiper A is moved to the center of the top “pot,” detail A,it would take off 12 volts; however, wiper B is taking off6 volts and the meter would read 6 volts, the differencebetween 6 and 12. Electrons would flow from B(negative) through the meter to A (positive in respect toB). The meter would be deflected to the left 6 volts, sowe can say the bridge is unbalanced to the left. Movingwiper B toward the positive potential and A towardnegative will cause the bridge to unbalance to the rightbecause current would flow from A to B, deflecting themeter to the right, which is demonstrated in detail B offigure 125.

3. Look at figure 126, a Wheatstone bridge. Thebasic operation is the same as the common bridge shownin figure 125, but it uses only one variable resistor.

4. The variable resistor has a higher resistancevalue than the three fixed resistors. When the variableresistor is centered, it has the same value as the fixedresistors; the bridge is in balance, for no voltage isindicated by the meter. Each resistor drops 12 volts.Detail A of figure 126 shows R4 unbalanced to the left.Because of its higher resistance, it now drops 18 of theapplied volts, and the remaining 6 volts are dropped byR1. The difference between 6 and 12 or 12

Figure 125. Simple bridge.

123

Figure 126. Wheatstone bridge.

and 18 is across the meter (6 volts). Since current flowsfrom negative to positive, the flow through the meter istoward the op of the page. Detail B of figure 126 showsR4 unbalanced to the right. This drops its value, causingmost of the applied voltage to be dropped across R1 (18volts). The difference between 12 and 18 (6 volts) isacross the meter, but in this case flowing toward thebottom of the page (- to +).

5. The Wheatstone bridge can be used on a.c. ord.c., but if a.c. is used, it requires a phase detector,discussed later in this chapter. The a.c. Wheatstonebridge is used with most electronic controls. Note that infigure 127 the d.c. power source has been replaced with atransformer and the voltmeter has been replaced with an

amplifier. The amplifier simply “builds up” the smallsignal from the bridge to operate a relay.

6. T1 (thermostat) now takes the place of R3. Thesensing element is a piece of resistance wire that changesin value as the temperature changes. An increase intemperature will cause a proportional increase inresistance. As you will note in figure 127, at set point of74° F., the bridge is in balance. The voltage at points Cand D is the same (7.5 volts), and the amplifier will keepthe final control element in its present position until wehave a temperature change. Now let’s assume the controlpoint changes.

7. When the temperature at T1 is lower than setpoint, its resistance is less than 1000 ohms. This lowerresistance causes more than 7.5 volts to be dropped byR2, which means that point C has a lower voltage thanpoint D. The amplifier will then take the necessaryaction to correct the control point.

8. When the temperature at T1 is higher than setpoint, its resistance is more than 1000 ohms, causing lessthan 7.5 volts to be dropped across R2. Point C has ahigher voltage than point D. The amplifier will onceagain take the necessary corrective action.

9. The resistance of T1 changes 2.2 ohms for eachdegree temperature change. This will cause only 0.0085-volt change between points C and D. For this reason, tocheck the bridge circuit, one will have to use anelectronic meter usually called a V.T.V.M. for vacuumtube voltmeter.

Figure 127. A.c. Wheatstone bridge.

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The vacuum tube voltmeter will usually have an ohmsscale as well as ac. and d.c. voltage scales.

10. The V.T.V.M. must be plugged into the lowerline for operation. Usually, there is no provision forcurrent measurements. Its advantage, however, is anextremely high input resistance of 11 million ohms (11meg) or more, as a d.c. voltmeter, resulting in negligibleloading effect. Also resistance ranges up to R X 1000allow measurements as high as 1000 megohms. Theohms scale reads from left to right like the volts scale andis linear without crowding at either end. Theadjustments are as follows:

(1) First, with the meter warmed up for severalminutes on the d.c. volts position of the selector switch,set the zero adjust to line up the pointer on zero at theleft edge of the scale.

(2) With the leads apart and the selector on ohms,the ohms adjust is set to line the pointer with maximumresistance ( ) at the right of the scale.

(3) Set the selector switch to the desired positionand use. The ohms adjust should be set for eachindividual range.

11. CAUTION: When checking voltage onunfamiliar circuits, always start with the highest voltagescale for your safety as well as protection of the meter.

12. Another circuit that you could use in electroniccontrols is the discriminator circuit. It is used inconjunction with a bridge circuit.

34. Discriminator Circuits

1. The purpose of the discriminator circuit is todetermine the direction in which the bridge is unbalanced

and take the necessary action to correct the condition.When the control point moves off set point, the bridgebecomes unbalanced and sends a small signal to thecontrol grid of the first-stage amplifier, as shown in figure128.

2. The small a.c. signal imposed on the control gridof this triode causes it to conduct more when the signalis positive and less when it is negative. The sine wave infigure 128 shows the plate voltage at point A. Note thatwhen the grid is more positive, the tube conducts moreand most of the 300 v.d.c. is dropped across load resistorR7. When the grid is negative, most of the voltage isdropped across the tube. The sine wave has beeninverted and is riding a fixed d.c. value of 150 volts.

3. The blocking capacitor C2 passes the amplifieda.c. component to the second stage but blocks the highvoltage d.c. R6 is the bias resistor for the control grid,and R5 is the bias bleeder to prevent self-bias.

4. Amplifier stages 2, 3, etc., as seen in figure 129,repeat the process until the signal is strong enough todrive a power tube or discriminator. At this point thesignal voltage has been amplified to a sufficient level todrive a power tube.

5. The power amplifier require a higher voltagedriving signal but controls a much larger current. Thiscurrent is then used to energize a relay and operates thefinal control element. In the discriminator circuit shownin figure 130, when the signal goes negative, cutoff bias isreached on the control grid. Also, the tube will conductonly when the plate is positive. Plate current willtherefore be similar to the output of a half-wave rectifier.

6. Since plate current flows in pulse, capacitor C5 isconnected across the coil of the motor relay. Thecapacitor will charge while the plate

Figure 128. Bridge and amplifier circuit.

125

Figure 129. Second- and third-stage amplification.

is conducting and discharge through the coil, holding itenergized during the off cycle. This type control is twoposition, and the final control will either be in the fullyopen or fully closed position.

7. The bridge supply voltage must come from thesame phase as the discriminator supply, shown in figure131. Supplying voltage from the same phase insures abridge signal that is either in phase or 180° out of phase

with the discriminator supply.

8. The control grid of the discriminator is biased atcutoff; therefore, it will conduct only when the plate andthe amplified bridge signal are both positive. With thetemperature below set point, as in figure 131, point C willhave the same polarity as point B (the resistance of T1

decreased); and will cause bridge signal to

Figure 130. Discriminator circuit.

126

Figure 131. Two-position control.

be more positive at the same time the discriminator plateis positive (solid symbols, +). Current flows through therelay and also charges capacitor C5. During the next half-cycle (dotted symbols, +) the signal is negative and thediscriminator plate is negative. No plate current canflow. Capacitor C5 discharges through the relay whichholds it closed until the next alteration.

9. The valve controlling chill water or brine willremain closed until the temperature increases. If thetemperature goes above the set point, the grid of thediscriminator will be negative when the plate is positiveand vice versa. No plate current can flow and the valveopens.

10. For modulating control, illustrated in figure 132,a modulating motor is used with a balancingpotentiometer. The balancing potentiometer is wired inseries with the thermostat resistor. Its purpose is to bringthe bridge back into balance (no voltage between pointsC and D) when a deviation has been corrected.Assuming a rise in temperature at T1 and the polarityshown by the solid symbols, point C will be negative.Neither of the discriminator tubes will conduct becausethe control grids of both are negative beyond cutoff bias.

During the next alternation (dotted symbols), when thesignal is positive, discriminator number 2 will conductbecause its plate is also positive. Capacitor C6 will chargeand relay number 2 will energize, causing the motor torun counterclockwise; this moves the wiper of thebalancing potentiometer to the right, adding resistance toR1, and removing resistance from T1 until no signal isapplied to the amplifier. Cutoff bias is reached on thecontrol grids of the discriminators, capacitor C6

discharges, relay 2 energizes, and the motor stops at itsnew position.

11. A decrease in temperature at T1, causes a 180°phase shift from the bridge. This phase shift places thegrid of discriminator tube 1 positive at the same time asthe plate. Relay 1 energizes and the motor runsclockwise until the bridge is once again balanced.

12. For control of relative humidity, the thermostatis replaced by a gold leaf humidistat. The principle ofoperation is the same; however, you must remember thatmoisture sensed by the gold leaf causes the resistance tochange.

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Figure 132. Modulating control.

Review ExercisesThe following exercises are study aids. Write your

answers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the text. Do not submit your answers.

1. Explain thermionic emission. (Sec. 29, Par. 3)

2. How does a directly heated cathode differ froman indirectly heated cathode? (Sec. 29, Par. 4)

3. Name the elements of a diode vacuum tube.(Sec. 29, Par. 7)

4. The electrons flow from the________________ to the_________________in a vacuum tube. (Sec.29, Par . 7)

5. Why does the diode rectify a.c.? (Sec. 29, Par.8)

6. What factors determine the amount of currentflowing through a diode tube? (Sec. 29, Par. 9)

7. The diode will conduct during the___________ half-cycle of the alternatingcurrent. (Sec. 29, Par. 11)

128

8. How can you filter half-wave rectification with acapacitor? (Sec. 29, Par. 13)

9. What is a duo-diode vacuum tube? (Sec. 2, Par.16)

10. What is the purpose of the control grid in avacuum tube? (Sec. 30, Par. 2)

11. Where, inside the tube, is the control gridphysically located? (Sec. 30, Par. 2)

12. The usual polarity of the grid with respect to thecathode is ________________. (Sec. 30,Par. 4)

13. What will happen to the current through a triodeif you make the control grid more negative?(Sec. 30, Par. 5)

14. Define grid bias. Cutoff bias. (Sec. 30, Pars. 5and 7)

15. Name the types of grid bias used on vacuumtubes. (Sec. 30, Pars. 8, 9, and 12)

16. What is one disadvantage of contact potentialbias? (Sec. 30, Par. 14)

17. Why can a triode be used as an amplifier? (Sec.30, Par. 15)

18. What is the potential of the screen grid withrespect to the cathode in a tetrode vacuum tube?(Sec. 30, Par. 19)

19. How does a power amplifier differ from a triodeamplifier? (Sec. 30, Par. 20)

20. What potential is applied to the suppressor gridof a pentode tube? (Sec 30, Par. 23)

21. What is a valence ring? (Sec. 31, Par. 4)

22. A valence ring containing two electrons indicatesa good ________________. (Sec. 31, Par. 4)

23. How is N-type germanium made? (Sec. 31, Par.8)

24. How does N-type germanium material differfrom P-type germanium material? (Sec. 31,Pars. 8 and 9)

25. To achieve reverse bias, the positive electrode ofthe battery is connected to the_______________ material and the negativeto the ________________ material. (Sec.31, Par. 13)

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26. Which type of bias encourages current flow?(Sec. 31, Par. 14)

27. How much power is developed in a circuithaving 100 ohms resistance and an amperagedraw of 5 amps? (Sec. 31, Par. 17)

28. Where is the base of a P-N-P transistor located?(Sec. 31, Par. 19)

29. How is maximum power gain obtained in atransistor? (Sec. 31, Par. 24)

30. What components of a vacuum tube arecomparable to the emitter, base, and collector ofa transistor? (Sec. 31, Par. 29)

31. Name the three basic transistor circuits. (Sec.32, Par. 1)

32. Which transistor circuit has a high impedanceinput and a low impedance output? (Sec. 32,Par. 5)

33. What is the purpose of a coupling capacitorbetween stages? (Sec. 32, Par. 6)

34. You are checking the voltage drop across apotentiometer. The applied voltage is 12 voltsand three-fourths of the resistance is in thecircuit. What is the voltage drop across thepotentiometer? (Sec. 33, Par. 1)

35. When is a simple two-resistor bridge balanced?(Sec. 33, Par. 2)

36. How is the Wheatstone bridge applied toelectronic control? (Sec. 33, Par. 5)

37. What will occur when the temperature at thethermostat, connected in a Wheatstone bridge,increases? (Sec. 33, Par. 8)

38. What type of meter is used to check outelectronic controls? Why? (Sec. 33, Par. 9)

39. What is the first step you must take when usinga V.T.V.M.? (Sec. 33, Par. 10)

40. What is the purpose of a discriminator circuit?(Sec. 34, Par. 1)

41. Explain the function of the blocking capacitor.(Sec. 34, Par. 3)

42. What has occurred when the signal in thediscriminator circuit goes negative? (Sec. 34,Par. 5)

43. Why should the bridge supply voltage comefrom the same phase as the discriminatorsupply? (Sec. 34, Par. 7)

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44. When will the discriminator circuit conduct?(Sec. 34, Par. 8)

45. Why is a balancing potentiometer read with amodulating motor? (Sec. 34, Par. 10)

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CHAPTER 7

Electronic Control Systems

ELECTRONIC control is here to stay. It has beenapproximately 16 years since the control industry firstshowed how microvoltages, electronically amplified, couldbe used in controlling air-conditioning and equipmentcooling systems. Despite an erroneous but perfectlyhuman awe in the presence of a revolutionary form ofpower, engineers, designers, and building owners began toapply this new type of control to their systems. Theordinary serviceman shunned electronic control becausethe thought that it was a piece of hardware too technicalto repair. By 1955, over 5000 electronic control systemswere in use, and it had become evident that theiradjustment and maintenance were not more difficult butactually simpler than those of the more traditional controlsystems--pneumatic and electric.

2. In this chapter you will study systemcomponents, applications, and the maintenanceperformed on electronic control systems.

35. Components

1. The components discussed in this section are thehumidity sensing element, thermostats, and dampermotor. The control panel will be discussed later in thischapter. It houses the bridge and amplifier circuits thatwe covered in Chapter 6.

2. Humidity Sensing Element. The sensingelement should be located within the duct at a placewhere the air is thoroughly mixed and representative ofaverage conditions. You must be careful not to locatethe sensing element too close to sprays, washers, andheating or cooling coils. The location should be within50 feet of the control panel. All wiring and mountingshould be accomplished as specified by the manufacturer.

3. Thermostats. The thermostats you will study inthis chapter are space, outdoor, and insertion. Inaddition, we will also cover thermostat maintenance.

4. Space thermostat. The thermostat should bemounted where it will be exposed only to typical or

average space temperature. You should avoid installing iton an outside wall or on a wall surface with hot or coldwater pipes or air ducts behind it.

5. In general, try to keep the thermostat out of theway of traffic, but in a representative portion of the spacebeing measured. The most desirable location is on aninside wall, 3 to 5 feet from the outside wall and about54 inches above the floor.

6. Outdoor thermostat. The sensing element is acoil of fine wire wound on a plastic bobbin and coatedfor protection against dirt and moisture. The thermostatshould be mounted out of the sun (on the north side ofthe building or in some other shaded location), above thesnowline, and where it won’t be tampered with.

7. Insertion thermostat. When using this thermostatas a discharge air controller, you should mount it farenough downstream from the coil to insure thoroughmixing of the air before its temperature is measured.When you use it as a return air controller, the thermostatis mounted where it will sense the average temperature ofthe return air from the conditioned space. If you mountit near a grille, it should be kept out of the airflow fromopen doors and windows.

8. To mount the thermostat, use the back of thebox as a template. Mark the four holes to be drilled inthe duct--the center hole and the three mounting holes.The center hole is used to insert the element.

9. Thermostat maintenance. To check the re-sistanceof the sensing element, you must disconnect one of theleads at the panel. Place an ohmmeter across the leads.Remember, allow for the temperature of the element andaccuracy of the meter.

10. A reading considerably less than the totalresistance specified indicates a short, either in theelement or in the leads to the element. If a short isindicated, take a resistance reading across the thermostatterminals. If the thermostat is shorted it must bereplaced. If the meter reads more than the totalresistance, there is an open

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Figure 133. Damper motor schematic.

circuit. Again, a reading across the thermostat terminalswill locate the trouble.

11. Excessive dirt accumulated on the element willreduce the sensitivity of the thermostat. Clean theelement with a soft brush or cloth. Be careful not todamage the resistance element.

12. Damper Motor. The motor may be installed inany location except where excessive moisture, acid fumes,or other deteriorating vapors might attack the metal. Themotor shaft should always be mounted horizontally.

13. The motor comes equipped with one crank arm.By loosening the screw and nut which clamp the crankarm to the motor shaft, the crank arm can be removedand repositioned in any one of the four 90° positions onthe motor shaft. The adjustment screw on the face ofthe crank arm provides angular setting of the crank armin steps of 22½° throughout any one of the four 90°angles. You can see by changing the position of the armon the square crankshaft and through the means of theadjustment screw on the hub, the crank arm may be setin steps of 22½° for any position within a full circle.The crank arm may be placed on either end of the motorshat.

14. For instructions in the assembly of linkages youmust refer to the instruction sheets packed in the cartonwith each linkage.

15. Motor Servicing. The only repairs that can beaccomplished in the field are cleaning the potentiometeror limit switch contacts, repairing internal connectingwires, and replacing the internal wires.

16. If the motor will not run, check the transformeroutput first. Look for the transformer in figure 133. If itchecks out good, use the transformer to check the motor.Disconnect the motor terminals (usually numbered 1, 2and 3) and connect the transformer output leads toterminals 2 and 3. The motor should run clockwise, if itis not already at that end of its stroke. Similarly,connecting the transformer across terminals 1 and 3should drive the motor counterclockwise.

17. If the motor responds to power from thetransformer, the fault probably lies in the relay, wiring, orpotentiometer. To check the potentiometer, disconnectterminals T, G, and Y from the outside leads. Theresistance of the potentiometer windings can now bechecked with an ohmmeter. The resistance across Y andG should be about 150 ohms. The resistance across Tand either Y or G should change gradually from near 0ohms about 135 ohms as the motor is driven through itsstroke.

18. If the motor does not respond to direct powerfrom the transformer, you must remove the motor coverand check for broken wires, defective limit switch, or afaulty condenser (capacitor).

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Figure 134. Refrigerant solenoid valve control system.

36. Application

1. The electronic control system has definitecharacteristics-flexibility, sensitivity, simplicity, speed, andaccuracy-that show to best advantage in an air-conditioning system where signals from severalcontrollers must be coordinated to actuate a series ofcontrol motors or valves. Each controller is a componentof a modified Wheatstone bridge circuit. A change inthe controlled variable will cause a change in the voltageacross the bridge. This change in voltage is detected byan electronic relay which starts corrective controlleddevice action. The magnitude of the voltage change andthe resulting device movement are a result of the amountof controlled variable change.

2. Authority “pots” in the control panel adjust thechange in variable required at a controller to give acertain voltage change. For example, an outdoorthermostat might be adjusted to require a 10°temperature change to give the same voltage change as a1° change at the space thermostat. For the remainder ofthis discussion, let us consider temperature as thecontrolled variable.

3. Voltages resulting from a rise in temperaturediffer in phase from voltages resulting from a drop intemperature and therefore can be distinguished. Voltagesresulting from temperature changes at several thermostatsare added in the bridge if they are of the same phase orsubtracted if they differ in phase. The total voltagedetermines the position of the final controlled device.Each controller directly actuates the final controlleddevice.

4. All adjustments for setting up or changing acontrol sequence can be made from the control panel.The panel may be mounted in any readily accessiblelocation. Selection of controls is simplified since oneelectronic control, with its broad range, replaces severalconventional controls where each has a smaller range.

5. The following systems are typical examples ofhow electronics is applied to the control of air-conditioning and equipment cooling systems. Thecontrol

sequence is given for each application.6. Refrigerant Solenoid Valve Control. The

electron control panel R1 in figure 134 will control spacetemperature by coordinating signals from the spacethermostat T1 and the outdoor thermostat T4 to operatethe refrigerant solenoid valve V1. T4 will raise the spacetemperature as the outdoor temperature rises to apredetermined schedule. T5 will remove T4 from thesystem when the outdoor temperature falls below thesetting of T5 to prevent subcooling of the space at lowoutdoor temperature.

7. You will find that a nonstarting relay, R2, iswired into the compressor starting circuit. This relay willprevent the compressor from operating unless thesolenoid valve is operating.

8. T1 is a space thermostat which may have anintegral set point adjustment and a locking cover. T4 andT5 are insertion thermostats.

9. Summer-Water Compensation for a Two-Position Heating or Cooling System. Controller T5shown in figure 135 will select either the summer orwinter compensation schedule. This selection dependsupon the outdoor temperature.

10. On the winter compensation schedule, electronicrelay panel R1 will control the space temperature bycoordinating signals from space thermostat T1 andoutdoor thermostat T3. The relay will operate either theheating or cooling equipment, depending upon the spacetemperature requirement. You can adjust the effect ofT3 to overcome system offset or to elevate the spacetemperature as the outdoor temperature falls.

11. During the summer compensation schedule, theelectronic panel will control temperature by coordinatingthe signals from T1 and the outdoor thermostat T4 tooperate the appropriate equipment, depending upon spacetemperature requirements. T4 will elevate the spacetemperature

Figure 135. Two-position heating and cooling system.

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as the outdoor temperature rises according to apredetermined schedule.

12. The last major topic that you will cover in thisvolume is maintenance of electronic controls.

37. Maintenance

1. In this section we shall discuss the adjustments,calibration, and calibration checks you will perform.After you have adjusted and calibrated the system, youwill learn how it operates. This system differs from thesystems previously discussed in that the electronic controlpanel controls a pneumatic relay. The section will beconcluded with a troubleshooting chart. With theinformation given in this section, you should have verylittle trouble acquiring the skill to perform most types ofmaintenance performed on electronic control systems.

2. Adjustments. You will find that the throttlingrange adjustment determines the temperature change atthe T1 thermostat. This adjustment will change thebranch line air pressure from 3 to 13 p.s.i.g. Anadjustable throttling range is commonly provided with arange from 1° to 50° F.

3. You should set the throttling range to as low avalue as possible without causing instability or hunting ofthe branch line pressure. If the controlled variable variescontinually and regularly reverses its direction, too low asetting of the throttling range is indicated. You mustincrease the throttling range until hunting stops.

4. Stable operation does not mean that the branchline pressure fails to change often; actually the controlsystem is extremely sensitive, and small temperaturechanges are being detected continuously. It is importantfor you to learn to distinguish between “jumpiness” and“hunting.” Jumpiness is caused by sensitivity of the relay,while hunting is a definite periodic alternating action.You must not interpret small gauge pressure fluctuationsas hunting. A condition of this type can be caused byresonance in the valve unit chambers.

5. The authority dials are graduated in percentages.These dials determine the respective authorities ofdischarge or outdoor thermostats with respect to thespace thermostat. The space thermostat is commonlyreferred to as T1. The remaining thermostats, outdoor,duct, etc., are numbered T2, T3, and T4. With anauthority of 25 percent, the outdoor thermostat is one-quarter as effective as the space thermostat. When youset the authority dials at zero percent, you are eliminatingall thermostats except T1 from the system. An authoritysetting of 5 percent means that a 20° change in outdoortemperature will have only as much effect as a 1° changeat the space thermostat.

6. You may find that the control panel has acontrol point adjuster. This adjuster makes it possible toraise or lower the control point after the system is inoperation. The control point adjuster is set at the timethe system is calibrated. The control point adjuster dialcontains as many as 60 divisions, each of which normallyrepresents a 1° change at the space thermostat.

7. The factory calibration and the valve unitadjustment can be checked or corrected only when thethrottling range knob is out. The factory calibration onmost systems is properly adjusted when it is possible toobtain a branch line pressure within 1 pound of 8 p.s.i.g.with an amplifier output voltage of 1 ± ¼ volt d.c. Ifthe calibration is not correct, you must turn the factorycalibration potentiometer until 1 volt is read from avoltmeter connected at the (+) terminal of the relay and(-) terminal of the bridge panel. A voltmeter of no lessthan 20,000 ohms per volt resistance must be used. Thenext step is to turn the valve unit adjusting screw untilthe branch line pressure is between 7 and 9 p.s.i.g.Clockwise rotation of the valve unit adjustment screwdecreases branch line pressure. The factory calibration isnow correctly set.

8. Calibration. Before you calibrate an electroniccontrol system you must determine the throttling rangeand the compensator authorities. Start your calibrationwith the adjustment knobs in the following positions:

(1) Control point adjuster: FULL COOL (2) Throttling range: OUT (3) Authority dials: 0

9. After the knobs are set, you must check thefactory calibration. The branch line pressure should be 8p.s.i.g. (±1 p.s.i.g). The actual branch line pressureobtained will be referred to as control reference pressure(CRP).

10. Next, you must measure the temperature at T1.This temperature will be referred to as the controlreference temperature (CRT). After you have obtainedthe two references, turn the throttling range to thedesired setting. At the same time, turn the control pointadjuster until the CRP is obtained (7-9 p.s.i.g.).

11. The authority dials are now set. Thisadjustment will change the branch pressure, so you mustreset the control point adjuster to maintain a CRP of 7-9p.s.i.g. The position of the control point adjusterrepresents the control reference temperature measured atT1. Increase or decease the temperature setting asdesired. Remember, each scale division is equal toapproximately 1° F.

12. If a space thermostat is not used, the

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calibration procedure will be the same, provided thedischarge controller is connected to T1 (T2 is not used)and T3 authority is turned to the desired setting f thedischarge controller is connected to the T3 position andT3 authority is tuned to the desired setting, the procedureis the same except that 70 F. is used as the CRT. Thecorrection for the desired set point is made with thecontrol point adjuster dial divisions representingapproximately ½° F each.

13. Calibration Check. The calibration of anysystem should be checked after the system has been putin operation. First, we will check a winter system.

14. At the no-load condition, the control point(measured space temperature) should be equal to the setpoint. On compensated systems, the control point shouldbe approximately equal to the set point, whereas on anuncompensated system, the control point will be slightlylower than the set point. On systems compensated toprovide successively higher temperatures as the outdoortemperature falls, the control point can be expected to behigher than the set point.

15. For any summer system, at the no-loadcondition, the control point should equal the set point. Ifthe outdoor temperature is above the no-load temperatureon an uncompensated system, you may consider itnormal because the control point will be slightly higherthan the set point. However, on systems compensated toprovide successively higher temperatures as the outdoortemperature rises, the control point can be expected to behigher than the set point.

16. To make a correction for a calibration error,simply rotate the control point adjuster the number ofdial divisions equal to the calibration error.

17. Operation. The one electronic controldiscussed here is similar to those in other panels; that is,it contains a modified Wheatstone bridge circuit whichprovides the input voltage for the electronic amplifier.The amplified output voltage is then used to control asensitive, high-capacity, piloted force-balance pneumaticvalve unit.

18. A change in temperature at T1 will initiatecontrol action by a signal from the bridge circuit.

Figure 136. Pneumatic valve unit.

This signal change provides a voltage to be fed to theamplifier which operates the pneumatic valve unit. Thesystem will then provide heating or cooling as requireduntil the initial signal is balanced by a change inresistance at T1 and T2 (depending upon the system’sschedule). An outdoor thermostat, T3, is used to measurechanges in outdoor temperature so that control action canbe initiated immediately before outdoor weather changescan be detected at T1. This in effect compensates forsystem off. The authority of T3 may be selected so thatin addition to compensating for offset, T3, will providesetup. For example, it will raise the system control pointas outdoor temperature drops.

19. The output of the electronic amplifier controlsthe current through the magnetic coil. Look at figure136 for the magnetic coil. As the voltage changes, thenozzle lever modulates over the nozzle. When the levermoves toward the nozzle, the branch line pressure willincrease. The new branch line pressure, through thefeedback bellows, opposes further movement of thenozzle lever. The forces which a upon the lever a nowin balance. When the voltage decreases, the lever willmove away from the nozzle. This movement will causethe branch line pressure to decrease until the forces areagain in balance.

20. Troubleshooting. Troubleshooting a suspecteddefective device can be speeded up by relating apparentdefects to possible causes. The troubleshooting guide,table 21, is broken up into portions related to the setupand calibration procedure given earlier.

TABLE 21

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TABLE 21-Continued

Review ExercisesThe following exercises are study aids. Write your

answers in pencil in the space provided after each exercise.Use the blank pages to record other notes on the chaptercontent. Immediately check your answers with the key at theend of the text. Do not submit your answers.

1. What precaution should you observe wheninstalling a humidity sensing element? (Sec. 35,Par. 2)

2. Describe the outdoor thermostat sensingelement. (Sec. 35, Par. 5)

3. How do you check the resistance of athermostat sensing element? (Sec. 35, Par. 9)

4. What factor will reduce the sensitivity of athermostat? (Sec. 25, Par. 11)

5. Explain the procedure you would use toreposition the crank arm on a damper motor.(Sec. 35, Par. 13)

6. Name the repairs that can be made to thedamper motor in the field. (Sec. 35, Par. 15)

7. How can you check the transformer output?(Sec. 35, Par. 16)

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8. What troubles may exist if the damper motordoes not respond to direct transformer power?(Sec. 35, Par. 18)

9. Which component in the control panel adjuststhe change in variable required at a controller togive a certain voltage change? (Sec. 36, Par. 2)

10. What factor determines the position of the finalcontrol element? (Sec. 36, Par 3)

11. Where are the adjustments made for setting upor changing a control sequence? (Sec. 36, Par.4)

12. Explain the function of the nonrestarting relay.Where is it connected? (Sec. 36, Par. 7)

13. How does the summer compensation schedulediffer from the winter compensation schedule?(Sec. 36, Pars. 10 and 11)

14. What has occurred when the controlled variablevaries continually and reverses its directionregularly? (Sec. 37, Par. 3)

15. With an authority setting of 10 percent, howmuch effect will t2 have when a 10°temperature change is felt? (Sec. 37, Par. 5)

16. How can you reset the control point after thesystem is in operation? (Sec. 37, Par. 6)

17. A trouble call indicates that an electronic controlsystem is not functioning properly. Thefollowing symptoms are present: (1) The amplifier output voltage is 1 volt.(2) The branch line pressure is 5 p.s.i.g. Whatis the most probable trouble? (Sec. 37, Par. 7)

18. What is the control reference temperature?Control reference pressure? (Sec. 37, Pars. 9and 10)

19. When checking the calibration of a compensatedsystem on winter schedule, what is therelationship of the control point to the set point?(Sec. 37, Par. 14)

20. How does a bridge signal affect the pneumaticrelay? (Sec. 37, Pars. 18 and 19)

21. What will happen if a faulty connection existsbetween the amplifier and bridge? (Sec. 37,table 21)

22. The tubes in the control panel light up and burnout repeatedly. Which components would youcheck? (Sec. 37, table 21)

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Answers to Review Exercises

1. The three things to consider before installing apreheat coil are necessity for preheat, enteringair temperature, and size of coils needed. (Sec.1, Par. 2)

2. The most probable malfunction when the streamvalve is closed and the temperature is 33° F. isthat the controller is out of calibration. (Sec. 1,Par. 4)

3. The two functions which the D/X coil servesare cooling and dehumidification. (Sec. 1, Par.7)

4. When a compressor using simple on-off controlshort cycles, the differential adjustment on thethermostat is set too close. (Sec. 1, Par. 9)

5. On a two-speed compressor installation, thehumidistat cycles the compressor from low tohigh speed when the space humidity exceeds theset point. (Sec. 1, Par. 11)

6. The nonrestarting relay prevents short cyclingduring the off cycle and allows the compressorto pump down before it cycles “off.” (Sec. 1,Par. 12)

7. When the solenoid valves are not operating, youshould check the operation of the fan becausethe fan starter circuit has to be energized beforethe control circuit to the valve can becompleted. (Sec. 1, Par. 14)

8. The type of compressor used when two-positioncontrol of a D/X coil and modulating control ofa face and bypass damper are used is a capacitycontrolled compressor. (Sec. 1, Par. 15)

9. An inoperative reheat coil. (Sec. 1, Par. 18) 10. The humidistat positions the face and bypass

dampers to provide a mixture of conditionedand recirculated air to limit large swings inrelative humidity. (Sec. 1, Par. 20)

11. The space humidistat has prime control of theD/X coil during light loads when a spacethermostat and humidistat are used to controlcoil operation. (Sec. 1, Par. 26)

12. The only conclusion you can make is that theunit is a “medium temperature unit.” Sec. 2. Par.3)

13. If you installed a medium temperature unit for a40° F. suction temperature application, themotor would overload and stop during peakload. (Sec. 2, Par. 3)

14. The low-pressure control will cycle the unitwhen the crankcase pressure exceeds the cut-inpressure setting of the control even though thethermostat has shut off the liquid line solenoidvalve. (Sec. 2, Par. 4 and fig. 19)

15. The automatic pump-down feature may beomitted when the refrigerant-oil ratio is 2:1 orless or when the evaporator temperature is above40° F. (Sec. 2, Par. 5)

16. Th four factors you must consider beforeinstalling a D/X system are space requirements,

equipment ventilation, vibration, and electricalrequirements. (Sec. 3, Par. 1)

17. To prevent refrigerant condensing in thecompressor crankcase, warm the equipment areaso the temperature will be higher than therefrigerated space. (Sec. 3, Par. 2)

18. The compressor does not require a specialfoundation because most of the vibration isabsorbed by the compressor mounting springs.(Sec. 3, Par. 3)

19. The minimum and maximum voltage that canbe supplied to a 220-volt unit is 198 volts to 242volts. (Sec. 3, Par. 5)

20. A 2-percent phase unbalance is allowablebetween any two phases of a three-phaseinstallation. (Sec. 3. Par. 5)

21. During gauge installation, the shutoff valve isback-seated to prevent the escape of refrigerant.(Sec. 3, Par. 9)

22. The liquid line sight glass is located between thedehydrator and expansion valve. (Sec. 3, Par.12)

23. Series. (Sec. 3, Par. 14) 24. Parallel. (Sec. 3, Par. 14) 25. Dry nitrogen and carbon dioxide are used to

pressurize the system for leak testing. (Sec. 3.Par. 15)

26. Moisture in the system will cause sludge in thecrankcase. (Sec. 3, Par. 16)

27. The ambient temperature (60° F.) allows themoisture to boil in the system more readily.This reduces the amount of time required fordehydration. (Sec. 3, Par. 17)

28. A vacuum indicator reading of 45° F.corresponds to a pressure of 0.3 inch Hgabsolute. (Sec. 3, Par. 18, fig. 17)

29. Shutoff valves are installed in the vacuum pumpsuction line to prevent loss of oil from thevacuum pump and contamination of the vacuumindictor. (Sec. 3, Par. 20)

30. Free. (Sec. 3, Par. 22) 31. The valves are backseated before installing the

gauge manifold to isolate the gauge ports fromthe compressor ports to prevent the entrance ofair or the loss of refrigerant. (Sec. 3, Par. 25)

32. The four items that you must check beforestarting a new compressor are the oil level, mainwater supply valve, liquid line valve, and powerdisconnect switch. (Sec. 3, Par. 26)

33. Frontseating the suction valve closes the suctionline to the compressor port, which causes thepressure to drop and cut off the condensing uniton the low-pressure control. (Sec. 3, Par. 34)

34. Placing a refrigerant cylinder in ice will cause thetemperature and pressure of the refrigerantwithin the cylinder to fall below that which isstill in the system. (Sec. 4, Par. 3)

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35. A partial pressure is allowed to remain in thesystem to prevent moist air from entering thesystem when it is opened (Sec. 4, Par. 4)

36. To prevent moisture condensation, you mustallow sufficient time for the component that isto be removed to warm to room temperature.(Sec. 4, Par. 6)

37. Basket; disc. (Sec. 4, Par. 9) 38. Noncondensable gases collect in the condenser,

above the refrigerant. (Sec. 4, Par. 10) 39. Noncondensable gases are present in the

condenser when the amperage draw is excessive,the condenser water temperature is normal, andthe discharge temperature is above normal.(Sec. 4, Par. 10)

40. A discharge pressure drop of 10 p.s.i.g. perminute with the discharge shutoff valvefrontseated would indicate a leaky compressordischarge valve. (Sec. 4, Par. 15)

41. Valve plates ere removed from cylinder deckswith jacking screws. (Sec. 4, Par. 18)

42. The emergency procedure you can use torecondition a worn valve is to lap the valve witha mixture of fine scouring powder andrefrigerant oil on a piece of glass in a figure 8motion. (Sec 4, Par. 21)

43. The oil feed guide is installed with the largediameter inward. Sec. 4, Par. 27)

44. A hook is used to remove the rotor to preventbending of the eccentric straps or connectingrods. (Sec. 4, Par. 29)

45. A small space is left to provide furthertightening in case of a leak. (Sec. 4, Par. 34)

46. 1.5 foot-pounds. (Sec. 4, Par. 35) 47. Check the start capacitor for a short when the

air conditioner keeps blowing fuses when it triesto start and the starting amperage draw is abovenormal. (Sec. 4, Par. 36)

48. A humming sound from the compressor motorindicates an open circuited capacitor. (Sec. 4Par. 36)

49. Closed. (Sec. 4, Par. 38) 50. Counter EMF produced by the windings causes

the contacts of the starting relay to open. (Sec.4, Par. 38)

51. Relay failure with contacts closed can causedamage to the motor windings. (Sec. 4, Par. 41)

52. Heater (and) control. (Sec. 4, Par. 43) 53. Oil pump discharge pressure; crankcase pressure.

(Sec. 4, Par. 44) 54. Disagree. The oil safety switch will close when

the pressure differential drops. (Sec. 4, Par. 45) 55. A burned-out holding coil or broken contacts

will cause an inoperative motor starter. (Sec. 4,table 1)

56. A restricted dehydrator is indicated when thedehydrator is frosted and the suction pressure isbelow normal. (Sec. 4, table 2)

57. The expansion valve is trying to maintain aconstant superheat. To accomplish this with aloose bulb, the valve is full open, which causesliquid refrigerant to flood back to thecompressor. (Sec. 4, table 5)

58. A low refrigerant charge (flash gas in the liquidline). (Sec. 4, table 6)

59. An excessive pressure drop in the evaporator.(Sec. 4, table 6)

60. The most probable causes for an exceptionallyhot water-cooled condenser are an overchargeand noncondensable gases in the system. Theseconditions may be remedied by bleeding thenon-condensables or excessive refrigerant fromthe condenser. (Sec. 4 , table 7)

61. An obstructed expansion valve. (Sec. 4, table10)

62. When a capacity controlled compressor shortcycles you must reset the compressor capacitycontrol range. (Sec. 4, table 10)

CHAPTER 2

1. The component that should be checked whenthe condenser waterflow has dropped off is thethermostat that controls the capacity controlvalve. The thermostat is located in the chillwater line. (Sec. 5, Par. 2)

2. Tap water; lithium bromide. (Sec. 5, Par. 3) 3. When heat is not supplied to the generator, the

salt solution in the absorber will become weakand the cooling action that takes place withinthe evaporator will stop. This will cause thechill water temperature to rise. (Sec. 5, Par. 5)

4. Disagree. It heats the weak solution. (Sec. 5,Par. 5)

5. The component is the capacity control valve.The reduced pressure will cause the thermostatto close the capacity control valve which reducesor stops the flow of water through thecondenser. The capacity of the system willdecrease without condenser waterflow. (Sec. 5,Pars. 6 and 7)

6. 4. (Sec. 5, Par. 7) 7. A broken concentration limit thermostat feeler

bulb will cause the vapor condensate welltemperature to rise because the capacity controlvalve will remain closed. (Sec. 5, Par. 8)

8. The chill water safety thermostat has shut theunit down because the leaving chill watertemperature was 12° above the designtemperature. To restart the unit, the off-run-start switch must be placed in the STARTposition so that the chill water safety thermostatis bypassed. After the chill water temperaturefalls below the setting of the chill water safetycontrol, the off-run-start switch placed in theRUN position. (Sec. 5, Pars. 9 and 10)

9. The pumps are equipped with mechanical sealsbecause the system operates in a vacuum. (Sec.5, Par. 14)

10. Disagree. It only controls the quantity of waterin the tank. It does not open a makeup waterline. (Sec. 5, Par. 14)

11. The nitrogen charge used during standby mustbe removed. (Sec. 6, Par. 3)

12. A low water level in the evaporator will causethe evaporator pump to surge. (Sec. 7, Par. 3)

13. A partial load. (Sec. 7, Par. 4) 14. The solution boiling level is set at initial startup

of the machine. (Sec. 7, Par. 5) 15. When air is being handled, the second stage of

the purge unit will tend to get hot. (Sec. 7, Par.7)

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16. Solution solidification. (Sec. 7, Par. 9) 17. You can connect the nitrogen tank to the

alcohol charging valve to pressurize the system.(Sec. 7, Par. 14)

18. Three. (Sec. 7, Par. 15) 19. You can determine whether air has leaked in the

machine during shutdown by observing theabsorber manometer reading and checking itagainst the chart. (Sec. 8, Par. 2)

20. Corrode. (Sec. 8, Par. 2) 21. To check a mechanical pump for leaks, you

must close the petcocks in the water line to thepump seal chamber and observe the compoundpressure gauge. A vacuum indicates a leaky seal.(Sec. 8, Par. 3)

22. Flushing the seal chamber after startup willincrease the life of the seal. (Sec. 8, Par. 4)

23. Chill water as leaked back into the machine.(Sec. 8, Par. 5)

24. Octyl alcohol is added to the solution to cleanthe outside of the tubes in the generator andabsorber. (Sec. 8, Par. 7)

25. When actyl alcohol is not drawn into the systemreadily, the conical strainer is dirty and must beremoved and cleaned. This is normallyaccomplished at the next scheduled shutdown.If this situation persists, the solution sprayheader must be removed and cleaned. (Sec. 8,Par. 8)

26. When the purge operates but does not purge, thesteam jet nozzle is plugged. To correct this, youmust close the absorber purge valve and thepurge steam supply valve. Then remove thesteam jet cap and clean the nozzle with a pieceof wire. The steam supply valve can be openedto blow out the loosened dirt. After the nozzleis clean, replace the cap and open the valves.(Sec. 8, Par. 9)

27. Silver nitrate. (Sec. 8, Par. 10) 28. Three drops of indicator solution is added to the

solution sample. (Sec. 8, Par. 10) 29. 1. (Sec. 8, Par. 11) 30. When more silver nitrate is needed to turn the

sample red, the sample contains more than 1percent of lithium bromide. The evaporatorwater must be reclaimed. (Sec. 8, Pars. 10 and11)

31. The length of time needed to reclaim evaporatorwater depends upon the amount of salt (lithiumbromide) in the evaporator water circuit. (Sec.8, Par. 12)

32. It takes 2 or 3 days for the dirt to settle outwhen the solution is placed in drums. (Sec. Par.14)

33. The conical strainer is cleaned by flushing itwith water. (Sec. 8, Par. 16)

34. The purge is cleaned with a wire or nylon brush.(Sec. 8, Par. 20)

35. Disagree. The diaphragm in a vacuum typevalve is replaced every 2 years. (Sec. 8, Par. 22)

36. A steady rise in vapor condensate temperatureindicates that the absorber and condenser tubesmust be cleaned. (Sec. 8, Par. 25)

37. Soft scale may be removed from the condenser

tubes with a nylon bristle brush. (Sec. 8, Par.28)

38. The maximum allowable vacuum loss during avacuum leak test is one-tenth of an inch of Hgin 24 hours. (Sec. 8, Par. 28)

39. The refrigerant used to perform a halide leaktest is R-12. (Sec. 8, Par. 29)

40. Three causes of lithium bromide solidification atstartup are condenser water too old, air inmachine, improper purging, or failure of strongsolution valve. (Sec. 8, table 11)

41. To check for a leaking seal, close the seal tankmakeup valve and note the water level in thetank overnight (Sec. 8, table 12)

CHAPTER 3

1. 1200 pounds. (Sec. 9, Par. 1) 2. The economizer reduces the horsepower

requirement per ton of refrigeration. (Sec. 9,Par. 2)

3. Disagree. The chilled water flows through thetubes. (Sec. 9, Par. 3)

4. Condenser float chamber. (Sec. 9, Par. 5) 5. The pressure within the economizer chamber is

approximately halfway between the condensingand evaporating pressures. (Sec. 9, Par. 5)

6. Line with the shaft. (Sec. 10, Par. 1) 7. The impellers are dipped in hot lead to protect

them from corrosion. (Sec. 10, Par. 2) 8. Two. (Sec. 10 Par. 3) 9. Brass labyrinth packing prevents interstage

leakage of gas. (Sec. 10, Par. 4) 10. Axial thrust will affect suction end of the

compressor. (Sec. 10, Par. 5) 11. Main compressor shaft. (Sec. 10, Par. 7) 12. The pump lubricates the thrust bearing first.

(Sec. 10, Par. 8) 13. Oil is returned from the oil pump drive gear by

gravity. (Sec. 10, Par. 9) 14. Oil pressure actuates the shaft seal. (Sec. 10,

Par. 10)15. The two holes in the inner floating seal ring

allow the passage of oil to the front journalbearing. (Sec. 10, Par. 11)

16. 8. (Sec. 10, Par. 12) 17. The oil pressure gauge located on the control

panel are the seal oil reservoir and “back ofseal.” (Sec. 3, Par. 13)

18. A flow switch in the water supply oil cooler lineturns the oil heater on automatically whenwaterflow stops. (Sec. 10, Par. 14)

19. Disagree. They are held apart during operation.(Sec. 10, Par. 16)

20. A high-grade turbine oil is used in centrifugalcompressors. (Sec. 10, Par. 17)

21. Increases. (Sec. 11, Par. 1) 22. Journal speed, tooth speeds, (and) clearances.

(Sec. 11, Par. 3) 23. The gear drive cooling water is turned on when

the oil temperature reaches 100° F. to 110° F.(Sec. 11, Par. 5)

24. Gear wear. (Sec. 11, Par. 9)

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25. The gear to compressor coupling uses a spoolpiece. (Sec. 12, Par. 1)

26. The hub is heated with oil, steam, or open flameto expand it: (Sec. 12, Par. 2)

27. Feeler gauge. (Sec. 12, Par. 3) 28. The offset alignment of a coupling is checked

with a dial indicator. (Sec. 12, Par. 4) 29. The couplings that have collector rings in the

end of the cover can be lubricated whilerunning. (Sec. 12, Par. 8)

30. Three; 60; adjustable speed wound. (Sec. 13,Par. 3)

31. Slipring circuit; speed. (Sec. 13, Par. 3) 32. When the start button is held closed, the oil

pressure switch is bypassed. (Sec. 13, Par. 4) 33. The secondary function of the condenser is to

collect and concentrate noncondensable gases.(Sec. 14, Par. 1)

34. A perforated baffle is used to prevent thedischarge gas from directly hitting the condensertubes. (Sec. 14, Par. 2)

35. When you remove the water box cover youmust leave two bolts in the cover until the coveris supported with a rope or chain. (Sec. 14, Par.3)

36. A blocked compressor suction opening. (Sec. 14,Par. 6)

37. Check the sight glass on the cooler to determinethe system refrigerant charge. (Sec. 4, Par. 11)

38. A load increase is indicated when the refrigerantand chill water temperature differential increases(Sec. 14, Par. 13)

39. Surging. (Sec. 15, Par. 1) 40. The liquid injector is used desuperheat the hot

gas (Sec. 15, Par. 2) 41. The pressure drop across the orifice created by

the flow of gas through the orifice controls theamount of liquid refrigerant flowing to the hotgas bypass. (Sec. 15, Par. 3)

42. Disagree. The high-pressure control resets auto-matically when the pressure falls to 75 p.s.i.g.(Sec. 16, Par. 3)

43. The weir and trap is located in the center of theevacuation chamber. (Sec. 16, Par. 3)

44. Air is in the system. (Sec. 16, Par. 5) 45. Air in the condenser is released through the

purge air relief valve. (Sec. 16, Par. 6) 46. One-half pint of water per day collected by surge

unit indicates leaky tubes. (Sec. 16, Par. 8) 47. A pressure drop will exist across the pressure-

regulating valve when it is wide open. (Sec. 16,Par. 9)

48. Large amounts of air are normally purged afterrepairs and before charging. (Sec. 16, Par. 10)

49. Water is drained from the separator unit when itcan be seen in the upper sight glass. (Sec. 16,Par. 12)

50. Low oil pressure, high condenser pressure, lowrefrigerant temperature, (and) low watertemperature. (Sec. 17, Par. 1)

51. The low oil pressure control does not require manual resetting. (Sec. 17, Par. 2)

52. The high condenser pressure control has adiffer-ential of 7 pounds. (Sec. 17, Par. 3)

53. You can change controllers with the rotaryselecting switch on the safety control panel.(Sec. 17, Par. 6)

54. Control the speed of the compressor. (Sec. 18,Pars. 1 and 2)

55. When you add more resistance to the rotorcircuit of the drive motor, the compressor speedwill decrease. (Sec. 18, Par. 3)

56. Suction damper control is more effective thanspeed control when it is necessary to maintain anon-surging operation at light loads. (Sec. 18,Par. 4)

57. During startup the drum controller lever is innumber 1 position, all resistance in the circuit tothe rotor. (Sec. 19, Par. 2)

58. Condensed refrigerant will cause the oil level torise in the pump chamber during an extendedshut-down. (Sec. 9,. Par 6)

59. 1. (Sec. 20, Par. 2) 60. Agree. The 2-inch plug does prevent leakage

when the ¾- inch plug is removed. (Sec. 20,Par. 3)

61. To charge refrigerant into the system as a gas,you must let the drum rest on the floor andopen the drum charging valve. (Sec. 20, Par. 5)

62. The system may be pressurized with the purgerecovery unit. (Sec. 20, Par. 6)

63. High condenser pressure is normally caused byair in the condenser. (Sec. 20, table 19)

64. Light load, air leak, (or) high condenser pressure.(Sec. 20, table 19)

65. When the economizer float valve is stuck, thecompressor second stage will frost. (Sec. 20,table 19)

66. Low “back of seal” oil pressure and a high sealoil pressure are caused by a dirty filter or a filtercartridge improperly installed. (Sec. 20, table 19)

67. Misalignment, insufficient lubrication, (or)excessive wear. (Sec. 20, table 19)

68. Agree. A high oil level will cause the gear tooverheat. (Sec. 20, table 19)

CHAPTER 4

1. The main scale-forming compound found incon-densing water systems is calcium carbonate.(Sec. 21, Par. 1)

2. 7.1 (to) 14; 200. (Sec. 21, Par. 4) 3. Using the formula

(Sec. 21, Par. 6) 4. Four methods of preventing scale are bleedoff,

pH adjustment, adding polyphosphates, andusing the zeolite softener. (Sec. 21, Par. 7)

5. Using the formula Hardness p.p.m. = 20 X (total No. of ml. of std.

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soap solution required to obtain a permanentlather)p.p.m = 20 X 10p.p.m = 200(Sec. 21, Par. 9)

6. The lime-soda process changes calcium andmagnesium from a soluble to an insoluble state.(Sec. 21, Par. 11)

7. The zeolite process replaces the calcium andmagnesium compounds with soluble sodiumcompounds. (Sec. 21, Par. 11)

8. It is necessary to add lime or clay to theAccelator to add weight which prevents risingfloc. (Sec. 21, Par. 15)

9. The factors that would limit the use of theSpiractor are excessive magnesium hardness,high water temperature, and turbidity over 5p.p.m. (Sec. 21, Par. 17)

10. A salt or brine solution is uniformly distributedon top of the zeolite bed, which passes evenlydown through the bed. (Sec. 21, Par. 18)

11. Corrosion is more rapid in a liquid with a lowpH value. (Sec. 22, Par. 2)

12. The most common type of corrosion in an acidliquid is uniform corrosion. (Sec. 22, Par. 4)

13. Pitting corrosion is characterized by cavities andgradually develops into pinhole leaks. (Sec. 22,Par. 5)

14. The type of corrosion that corrodes steel in asystem that contains an abundance of copper isknown as galvanic corrosion. (Sec. 22, Par. 6)

15. Erosion-corrosion is caused by suspended matteror air bubbles; the best control for this type ofcorrosion is a good filtration system, and airpurging valves installed in the highest point ofthe water system. (Sec. 22, Pars. 7 and 8)

16. The two most common chemical corrosioninhibitors are chromates and polyphosphates.(Sec. 22, Par. 10)

17. 200 (to) 500 p.p.m.; 7.5. (Sec. 22, Par. 11)18. The most common chromate used is sodium

bichromate because it is more economical thanothers. (Sec. 22, Par. 11)

19. The chromate concentration of treated water ismeasured by color comparison of the sample tothat of a tube chromate water known to containa certain p.p.m. of chromate. (Sec. 22, Par. 14)

20. High concentration of polyphosphates precipitateout in the form of calcium phosphate. (Sec. 22,Par. 14)

21. First of all, there is no yellow residue producedby polyphosphates, as there is by chromates.Secondly, polyphosphates reduce sludge and rust(tuberculation). (Sec. 22, Par. 15)

22. Bleedoff must be adjusted on condenser watersystems using polyphosphates to avoid exceedingthe solubility of calcium phosphate. (Sec. 22,Par. 16)

23. The chemical corrosion inhibitors that are in anylon net bag which is placed in a cooling towermay be in pellet or crystal form. (Sec. 22, Par.18)

24. Chilled water and brine solution systems requirethe pot type corrosion inhibitor feeders. (Sec.22, Par. 18)

25. Algae formations will plug the nozzles in

cooling towers, thus causing high condensingtemperatures and reducing the system’s capacity.(Sec. 23, Par. 1)

26. The amount of chlorine needed to eliminatealgae growth is 1.5 p.p.m. (Sec. 23, Par. 2)

27. Disagree. The sample is heated after theorthotolidine is added. (Sec. 23, Par. 3)

28. Chlorination is effective because the bactericidalefficiency of chlorine increases with the increasein the temperature of the water. (Sec. 23, Par.6)

29. The orthotolidine test measures only the totalavailable chlorine residual, while theorthotolidine-arsenite test measures the relativeamounts of free available chlorine, combinedavailable chlorine, and color caused byinterfering substances. (Sec. 23, Par. 8)

30. The combined available chlorine residual is 3.25– 2.5 = .75 p.p.m. (Sec. 23, Par. 9)

31. To perform a chlorine demand test, you mustfirst prepare a test sample by mixing 7.14 gramsof calcium hypochlorite with 100 cc. Of waterto produce a 5000 p.p.m. chlorine solution. Add1 milliliter of this sample to the water to betested. Wait 30 minutes and perform a chlorineresidual test. You must then subtract thechlorine residual from the test dosage to obtainthe chlorine demand. (Sec. 23, Pars. 13, 14, and15)

32. To perform the pH determination with a colorcomparator, you would fill the color comparatortube with the sample to be tested to theprescribed mark on the tube. The you wouldadd 0.5 ml. mark on the tube. Then you wouldadd 0.5 ml. of cresol red-thymol blue solution tothe sample. After mixing the solutionthoroughly in the sample, you would place thesample tube in the comparator and match thesample color with the cresol red-thymol bluedisc. (Sec. 23, Pars. 17, 18, and 19)

33. Alkaline, because a pink color indicates a pHabove 8.3. (Sec. 23, Par. 22)

34. Sulfuric, sodium sulfate, and phosphoric acidsare added to adjust the pH. They are added tothe water through a solution feeder. (Sec. 23,Par 24)

35. Calcium hypochlorite contains more chlorine byweight; 65 to 70 percent available chlorine byweight. (Sec. 23, Pars. 26 and 27)

36. To add 100 gallons of chlorine solution per day,you would select the Wilson type DEShypochlorinator because its capacity is 120gallons per day. (Sec. 23, Par. 32)

37. 4.

38. You would have to add 43 pounds of HTH tothat water which requires 30 pounds of chlorine.

39. Thirty gallons of chlorine is added per day totreat

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2 million gallons of water when the dosage is 1.5p.p.m. and dosing solution is 10 percent.

40. The precautions that must be followed whileper-forming the turbidimeter test are as follows:The glass tube must be placed in a verticalposition with the centerlines matched. The topof the candle support should be 3 inches belowthe bottom of the tube. The candle must bemade of beeswax and spermaceti, gauged toburn within 114 and 126 grains per hour. Theflame must be a constant size and the samedistance below the tube. The tube should beinclosed in a case when observations are made.Soot, moisture and impurities must not beaccumulated on the bottom of the glass tube.(Sec. 24, Pars. 4, 5, and 6)

41. The number of gallons that a vertical typepressure filter, 4 feet in diameter, can treat in 1hour is:

Area = π2

Area = 3.146 X (1/2d)Area = 3.146 X (2 X 2)Area = 3.146 X 4Area = 12.564 or 12.6

12.6 X 3 = 37.837.8 X 60 =2268 gallons.

(Sec. 24, Par. 11)42. The precaution for taking water samples that is

common to both types of analysis is that theequipment (bottle, stopper, etc.) must besterilized. (Sec. 25, Pars. 3 and 4)

43. To sterilize a bottle that is to be used forchlorine rating 0.2 to 0.5 grams of sodiumthiosulfate is added to the sample in the bottle.Then it is sterilized at a temperature below 392°to prevent decomposition of the thiosulfate (Sec.25, Par. 4, a)

44. You should hold the bottle least 3 inches belowthe surface of water in a tank when you take asample. (Sec. 25, Par. 4, c)

45. A solution of lysol, mercuric chloride, or ofbicarbonate of soda is used to rinse your handsafter making water tests. (Sec. 25, Par. 7)

CHAPTER 5

1. The amount of cement that you would mix with12 pounds of sand and 24 pounds of crushedrock is 4 pounds. (Sec. 26, Par. 1)

2. A 1-inch space is left between the foundationand baseplate to allow enough room for groutingafter the baseplate is level. (Sec. 26, Par. 1)

3. A ¾- inch baseplate bolt requires a sleeve madefrom 1.875-inch pipe. (Sec. 26, Par. 1)

4. To level the baseplate, you would place twowedges below the center of the pump and two abelow the center of the motor. (Sec. 26, Par. 3)

5. The angular alignment of a “spider” is checkedat four points on the circumference of the outerends of the coupling hubs at 90° intervals. (Sec.26, Par. 4)

6. Angular alignment is accomplished by looseningthe motor holddown bolts and shifting orshimming the motor. (Sec. 26, Par. 5)

7. To grout the unit, you must build a wooden damaround the foundation and wet the top of thefoundation. Then fill the space with grout.(Sec. 26, Par. 7)

8. One part of Portland cement to three parts ofsharp sand is used to make grout. (Sec. 26, Par.7)

9. You should allow 48 hours for the grout toharden. (Sec. 26, Par. 7)

10. To establish initial alignment of the pumpingunit, you must tighten the foundation andholddown bolts. Check the gap, angularadjustment, and parallel alignment. Recheckalignment after each adjustment. (Sec. 26, Par.9)

11. The unit may become misaligned because offoundation settling, seasoning, or springing; pipestrains; shifting of the building structure; orspringing of the baseplate. (Sec. 26, Par. 9)

12. Strainer. (Sec. 26, Par. 10) 13. The pump will lose a and capacity if smaller

discharge pipe is installed. (Sec. 26, Par. 11) 14. To prime the pump, fill it with the fluid to be

pumped through the priming opening in thepump. (Sec. 27, Par. 1)

15. After the pump is primed and before it isstarted, make sure that all the pump connectionsare airtight and rotate the pump shaft by handto be sure that it moves freely. (Sec. 27, Par. 1)

16. Loose pump connections, low liquid level in thepump, loose suction line joints, improperdirection of rotation, motor not up to nameplatespeed, and dirty suction strainer will cause thefailure of a newly installed pump. (Sec. 27, Par.3)

17. The lantern ring. (Sec. 28, Par. 2) 18. You must pipe clean water to the stuffing box

when the water being pumped is dirty, gritty, oracidic. (Sec. 28, Par. 3)

19. Loose packing will leak excessively and tightpacking will burn and score the shaft. (Sec. 28,Par. 4)

20. When five-ring packing is used, stagger thepacking joints approximately 72°. (Sec. 28, Par.5)

21. Back off the gland bolts. (Sec. 28, Par. 10) 22. The bellows should not be disturbed unless it is

to be replaced. (Sec. 28, Par. 11) 23. The four types of bearings found in centrifugal

pumps are grease-lubricated roller and ballbearings, oil-lubricated ball bearings, and oil-lubricated sleeve bearings. (Sec. 28, Par. 17)

24. Overlubrication causes overheated bearings.(Sec. 28, Par. 17)

25. Mineral greases with a soda soap base arerecommended for grease lubricated bearings.(Sec. 28, Par. 19)

26. Vegetable and animal greases are not used tolubricate pump bearings because they may formacid and cause deterioration. (Sec. 28, Par. 19)

27. 180° F. (Sec. 28, Par. 20) 28. 150° F. (Sec. 28, Par. 22) 29. The four drilled recesses facilitate the removal

and

144

installation of the coupling bushing. (Sec. 28,Par. 24)

30. Disagree. The recessed holes should face awayfrom the pump. (Sec. 28, Par. 26)

Chapter 6

1. Thermionic emission is a method of emittingelectrons from the cathode with heat. (Sec. 29,Par. 3)

2. In a directly heated cathode, the material thatheats also emits electrons, whereas the indirectlyheated cathode has separate heating and emitterelements. (Sec. 29, Par. 4)

3. The elements of a diode vacuum tube are thecathode and plate. (Sec 29, Par. 7)

4. Cathode; plate. (Sec. 29, Par. 7)5. The diode rectifies a.c. because current will pass

through the tube in one direction. (Sec. 29, Par.8)

6. The factors that determine the amount ofcurrent flowing through a diode tube are thetemperature of the cathode and the potentialdifference between the cathode and plate. (Sec.29, Par. 9

7. Positive. (Sec. 29, Par. 11)8. The capacitors will filter half-wave rectification

by charging during the positive half-cycle anddischarging through the load resistance duringthe negative half-cycle. (Sec. 29, Par. 13)

9. A duo-diode is a tube containing two diodetubes. It may have one cathode and two plates.(Sec. 29, Par. 16)

10. The purpose of the control grid is to providemore sensitive control of the plate current. (Sec.30, Par. 2)

11. The control grid is physically located betweenthe cathode and plate. (Sec. 30, Par. 2

12. Negative. (Sec. 30, Par. 4)13. When the grid is made more negative, the

current through the tube will decrease. (Sec. 30,Par. 5)

14. Grid bias is the potential difference of the d.c.voltage on the grid with respect to the cathode.Cutoff bias is the point at which the negativegrid voltage stops all current flow in the tube.(Sec. 30, Pars. 5 and 7)

15. The types of grid bias used on vacuum tubes arefixed, cathode, and contact potential. (Sec. 30,Pars. 8, 9, and 12)

16. A disadvantage of contact potential bias is thatbias is developed only when a signal is applied tothe grid. (Sec. 30, Par. 14)

17. The triode can be used as an amplifier because asmall a.c. voltage applied between the cathodeand grid will cause a change in at grid bias andvary the current passing through the tube. (Sec.30, Par. 15)

18. The potential of the screen grid is positive withrespect to the cathode. (Sec. 30, Par. 19)

19. The power amplifier handles larger values ofcurrent than triode amplifiers. (Sec. 30, Par. 20)

20. A negative potential is applied to the suppressorgrid of a pentode tube. (Sec. 30, Par. 23)

21. The valence ring is the outer ring or orbit of anatom. (Sec. 31, Par. 4)

22. Conductor. (Sec. 31, Par. 4)23. N-type germanium is made when an antimony

atom has gone into covalent bonding withgermanium. The antimony in the materialdonates a free electron. (Sec. 31, Par. 8)

24. N-type material has free electrons which supportelectron flow, whereas P-type material has ashortage of electrons. This shortage causescurrent to flow from the N-type material to theP-type material. (Sec. 31, Pars. 8 and 9)

25. N-type; P-type. (Sec. 31, Par. 13)26. Forward bias encourages current flow. (Sec. 31,

Par. 14)27. 2500 watts is developed in a circuit having 100

ohms resistance and an amperage draw of 5amps (P = I2R). (Sec 31, Par. 17)

28. The base is located between the emitter andcollector. (Sect. 31, Par. 19)

29. Maximum power gain is obtained by making thebase region very narrow compared to the emitterand collector regions. (Sec. 31, Par. 24)

30. The emitter is comparable to the cathode, thebase to the grid, and the collector to the plate.(Sec. 31, Par. 29)

31. The three basic transistor circuits are thecommon base, common emitter, and commoncollector. (Sec. 32, Par. 1)

32. The common collector circuit has a highimpedance input and a low impedance output.(Sec. 32, Par. 5)

33. The coupling capacitor is used to couple thesignal into the emitter-base circuit of thetransistor. (Sec. 32, Par. 6)

34. The voltage drop is 9 volts (3/4 X 12 = 9).(Sec. 33, Par. 1)

35. A simple two-resistor bridge is balanced whenno current flows between the wipers. (Sec. 33,Par. 2)

36. The Wheatstone bridge sends a signal to theamplifier, which builds up the bridge signal tooperate a relay. (Sec. 33, Par. 5)

37. The higher temperature will unbalance thebridge by increasing the resistance in one circuit.The signal from the bridge will be amplified andoperate a relay. (Sec. 33, Par. 8)

38. A vacuum tube voltmeter is used because it hasa high input resistance. (Sec. 33, Par. 9)

39. The first step to take when using a V.T.V.M. isto turn the meter on and allow it to warm up.(Sec. 33, Par. 10)

40. The purpose of the discriminator circuit is todetermine in which direction the bridge isunbalanced and take the necessary action tocorrect the condition. (Sec. 34, Par. 1)

41. The function of the blocking capacitor is to passa.c. to the second stage and block the high-voltage d.c. (Sec. 34, Par. 3)

42. When the signal in the discriminator circuit goesnegative, the cutoff bias is reached on thecontrol grid. (Sec. 34, Par. 5)

43. The bridge supply voltage should come from thesame phase as the discriminator supply to insurea bridge signal that is either in phase of 180° outof

145

phase with the discriminator supply. (Sec. 34,Par. 7)

44. The discriminator circuit will conduct when theplate and the amplified bridge signal are bothpositive. (Sec. 34, Par. 8)

45. A balancing potentiometer is used with amodulating motor to bring the bridge back intobalance when a deviation has been corrected.(Sec. 34, Par. 10)

Chapter 7

1. The precaution you should observe wheninstalling a humidity sensing element is to locateit not too close to sprayers, washers, and heatingor cooling coils, but within 50 feet of the controlpanel. (Sec. 35, Par. 2)

2. The outdoor thermostat sensing element is a coilof fine wire wound on a plastic bobbin andcoated for protection against dirt and moisture.(Sec. 35, Par. 5)

3. To check the resistance of the sensing element,disconnect the leads and connect an ohmmeteracross them. (Sec. 35, Par. 9)

4. Dirt on the sensing element will reduce thesensitivity of a thermostat. (Sec. 35, Par. 11)

5. To reposition the crank arm on the dampermotor shaft, loosen the screw and nut that holdthe arm on the shaft. This will allow you toreposition the shaft in four different positions,90° apart. The adjustment screw on the face ofthe crank arm provides angular setting of thecrank arm in steps of 22 1/2° throughout anyone of the four positions on the shaft. (Sec. 35,Par. 13)

6. The damper motor repairs that may be made inthe field are cleaning the potentiometer or limitswitch contacts, repairing internal connectingwires, and replacing the internal wires. (Sec. 35,Par. 15)

7. You can check the transformer output byconnecting a voltmeter across its terminals.(Sec. 35, Par. 16)

8. If the damper motor does not respond to directtransformer power, the most probable faults arebroken wires, defective limit switch, or faultycondenser. (Sec. 35, Par. 18)

9. The authority “pots” adjust the change invariable required to give a certain voltagechange. (Sec. 36, Par. 2)

10. The total voltage across the bridge determinesthe position of the final control element. (Sec.36, Par. 3)

11. The adjustments for setting up or changing acontrol sequence are made at the control panel.(Sec. 36, Par. 4)

12. The nonrestarting relay is connected in thecompressor starting circuit. It will prevent thecompressor from operating unless the solenoidvalve is operating. (Sec. 36, Par. 7)

13. The summer compensation schedule differsfrom the winter compensation schedule in thatoutdoor thermostat T3 will be replaced by T1.(Sec. 36, Pars. 10 and 11)

14. When the controlled variable varies continuallyand reverses its direction regularly, the throttlingrange is set too low. (Sec. 37, Par. 3)

15. With a 10 percent authority and 10° temperaturechange T3 will have the same effect as a 1°change in temperature at T1. (Sec. 37, Par. 5)

16. The control point can be reset after the systemis in operation by positioning the control pointadjuster in the control panel. (Sec. 37, Par. 6)

17. When the amplifier output voltage is 1 volt andthe branch line pressure is 5 p.s.i.g., the mostprobable trouble is that the valve unit is out ofadjustment. (Sec. 37, Par. 7)

18. The control reference temperature istemperature measured at T1. The controlreference pressure is the actual branch linepressure. (Sec. 37, Pars. 9 and 10)

19. The control point of a compensated system onwinter schedule should be equal to the set point.(Sec. 37, Par. 14)

20. The bridge signal is amplified and fed to amagnetic coil in the pneumatic valve. Theamount of current flowing through the coilpositions nozzle lever over the nozzle. Theposition of this lever controls the amount ofbranch line pressure sent to the controlleddevice. (Sec. 37, Pars. 18 and 19)

21. A faulty connection between the amplifier andbridge will cause one or more of the tubes toremain cold. (Sec. 37, table 21)

22. The transformer output and the valve unit relaymust be checked when the tubes light up andburn out repeatedly. (Sec. 37, table 21)

*U.S. Government Printing Office: 2001-628-075/40468

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