documentq
TRANSCRIPT
Q.1)
The capacity of an evaporator is affected by ____.
A.
the saturation pressure of the low side of the system
B.
the saturation pressure of the high side of the system
C.
the amount of evaporator superheat
D.
all of the above
Q.2)
A forced draft medium temperature evaporator would ____.
A.
be defrosted by off-cycle defrost
B.
not need to be defrosted
C.
need electric defrost
D.
need a hot gas defrost
Q.3)
A forced draft high temperature evaporator would ____.
A.
have its fins very close together
B.
not need to be defrosted
C.
need a hot gas defrost
D.
both a and b
Q.4)
During the defrost cycle of a forced draft low temperature evaporator, the evaporator fan would ____.
A.
remain on to speed up the defrost
B.
turn off
C.
cycle with the condenser
D.
cycle with the compressor
Q.5)
If an evaporator has a pressure drop of 10 psig and the low side pressure is 15 psig, what is the pressure at the inlet of the evaporator?
A.
10 psig
B.
25 psig
C.
15 psig
D.
5 psig
Q.6)
Excess evaporator superheat ____.
A.
is desired to prevent liquid from entering the compressor
B.
will reduce the cooling capacity of the system
C.
can be removed by removing refrigerant from the system
D.
will cause the system to go into defrost
Q.7)
If a low temperature evaporator is forming excess ice, which of the following could be a possible problem?
A.
The evaporator fan motor is defective.
B.
The unit is not staying in defrost long enough.
C.
The defrost heater is defective.
D All of the above are
. correct.
Q.8)
If a high temperature evaporator is forming ice, which of the following is a possible problem?
A.
evaporator fan not running
B.
compressor not running
C.
condenser fan not running
D.
no problem, ice formation normal
Q.9)
If a low temperature evaporator is forming ice, which of the following is a possible problem?
A.
evaporator fan not running
B.
compressor not running
C.
condenser fan not running
D.
no problem, ice formation normal
Q.10)
If an R-12 refrigeration system is operating with a 25.4 psig suction pressure, what is the evaporator superheat if the evaporator outlet temperature is 34°F?
A.
9°F
B.
59°F
C.
34°F
D.
25°F
Q.11)
A typical evaporator operating temperature in an air-conditioning system is ____.
A 40°
. F
B.
55°F
C.
75°F
D.
200°F
Q.12)
A large capacity evaporator would probably have ____.
A.
stainless steel tubing
B.
an excess of liquid refrigerant
C.
an excess of vapor refrigerant
D.
multiple refrigerant circuits
Q.13)
If the application requires a coil design to operate below 32°F, there must be provision for ____.
A.
flooding the evaporator
B.
adding the evaporator
C.
defrost
D.
suction pressure control
Q.14)
The heat required for off-cycle defrost is obtained from ____.
A.
supplemental electric heat when the system is shut down
B.
hot gas when the system is operating
C.
the space temperature when the compressor is off
D.
the space temperature when the compressor is off
Q.15)
A direct expansion-type evaporator is also called a ____.
A.
flooded evaporator
B.
dry-type evaporator
C.
multi-circuit evaporator
D.
stamped evaporator
Q.16)
A refrigeration system designed for the storage of flowers or candy is considered a ____ type.
A.
high temperature
B.
medium temperature
C.
low temperature
D.
sharp freezing
Q.17)
A typical superheat for an evaporator operating under normal conditions would be ____.
A.
14 to 16°F
B.
4 to 6°F
C.
8 to 12°F
D.
6 to 8°F
Q.18)
When a system with a water-cooled condenser cycles off, the water regulating valve should ____.
A.
remain open during the off cycle
B.
close, since the head pressure is lower
C.
open all the way to remove any residual heat
D.
re-calibrate itself to maintain the new lower head pressure
Q.19)
A normally operating water-cooled condenser is operating with a 10° differential between water in and water out. If the amount of 85°F water going through the condenser is reduced, which of the following is a possible temperature of the water leaving the condenser?
A.
75°F
B.
0°F
C.
95°F
D.
105°F
Q.20)
A normally operating water-cooled condenser is operating with a 10° differential between water in and water out. If scale forms on the water tubes and the entering water is 85°F, which of the following is possible?
A.
The outlet water will be 88°F.
B.
The system head pressure will rise
C.
The water regulating valve will close.
D.
Both a and b are correct.
Q.21)
Which of the following would allow a system to operate more efficiently?
A.
condenser that had refrigerant leaving with 10°F of superheat
B.
condenser that had refrigerant leaving with 15° of subcooling
C.
condenser that had refrigerant leaving as 100% vapor
D.
condenser that had refrigerant leaving with 10° of subcooling
Q.22)
If an R-12 refrigeration system has its air-cooled condensing unit on a 100°F roof and the condenser outlet temperature (refrigerant) is 115°F, with how much subcooling is the condenser operating?
A.
30°F
B.
15°F
C.
100°F
D.
130°F
Q.23)
Which of the following condensers is the most efficient?
A.
forced draft air-cooled
B.
induced draft air-cooled
C.
water-cooled parallel flow
D.
water-cooled counter flow
Q.24)
An air-cooled condenser that is operating in a climate that has four distinct seasons must ____.
A.
have some type of head pressure control
B.
use a water regulating valve
C.
have a multi-circuit evaporator
D.
operate with zero degrees of subcooling
Q.25)
What can be used to maintain the head pressure of a system with a water-cooled condenser?
A.
fan cycling
B.
dampers or louvers
C.
water regulating valve
D.
all of the above
Q.26)
Which of the following can be used to maintain the head pressure of a system with an air-cooled condenser?
A.
fan cycling
B.
condenser flooding valve
C.
dampers or louvers
D.
all of the above
Q.27)
The refrigerant in a condenser in a refrigeration system ____.
A.
absorbs heat
B.
gives up heat
C.
changes to a vapor
D.
is under lower pressure than the evaporator
Q.28)
The condenser in a refrigeration system ____.
A.
desuperheats the vapor from the compressor
B.
condenses the vapor from the compressor
C.
subcools the liquid refrigerant before it leaves the condenser
D.
all of the above
Q.29)
Mineral deposits in the water portion of a water-cooled condenser act as ____.
A.
a conductor of heat
B.
an insulator
C.
a cleaning solution
D.
They have no effect on the operation of the condenser.
Q.30)
The water circuit in shell and coil and coil-type tube-in-a-tube condensers must be cleaned ____.
A.
by removing the end caps
B.
with a brush
C.
chemically
D.
by air pressure
Q.31)
The shell and tube condenser is cleaned ____.
A.
with a brush after removing the end caps
B.
only with chemicals
C with
. compressed air
D.
with a vacuum cleaner
Q.32)
If the waterflow is reduced, the temperature difference across a condenser will ____.
A.
increase
B.
decrease
C.
remain the same
D.
correspond to the evaporator saturation temperature
Q.33)
In a water-cooled condenser, a regulating valve is used to control the ____.
A.
refrigerant flow through the pressure reducing device
B.
refrigerant condensing temperature
C.
suction pressure
D.
water temperature
Q.34)
Control of the head pressure in an air-cooled condenser is done by ____.
A.
cycling the condenser fan
B.
controlling dampers in the airstream through the condenser
C.
flooding the condenser with refrigerant
D.
all of the above
Q.35)
In a water-cooled condenser with dirty condenser tubes, the temperature difference between the refrigerant and the leaving water will be ____ when the
tubes are clean.
A.
less than
B.
greater than
C.
the same as
D.
slightly lower than
Q.36)
Condensing temperatures in an air-cooled condensing unit can be reduced by ____.
A.
increasing the condensing surface area
B.
increasing the cfm through the condenser
C.
decreasing the temperature of the air entering the condenser
D.
all of the above
Q.37)
A stamped plate evaporator usually does not use a fan to move air across it.
A.
True
B.
False
Q.38)
When the velocity of the air moving over an evaporator is slow, the "air film" acts as an insulator and slow the rate of heat exchange.
A.
True
B.
False
Q.39)
The refrigerant in the evaporator must be colder than the air passing over it for heat to transfer to the evaporator.
A.
True
B.
False
Q.40)
The device used to feed refrigerant to multiple circuits in an evaporator is called a flow circuit.
A.
True
B.
False
Q.41)
Fewer fins per inch on an evaporator allow more ice to build between defrost cycle.
A.
True
B.
False
Q.42)
Every central split cooling system manufactured in the USA today must have a Seasonal Energy Efficiency Ratio (Seer) of at least 10.
A.
True
B.
False
Q.43)
A water regulating valve helps maintain in a system's head pressure by modulating the flow of refrigerant through the condenser.
A.
True
B.
False
Q.44)
Evaporative condensers operate more efficiently in climates where the wet bulb temperature is a great deal lower than the dry bulb temperature.
A.
True
B.
False
Q.45)
The desired water flow through a condenser connecting to a recirculating water system is 3 gallons per minute.
A.
True
B.
False
Q.46)
If a spring pressure of a water regulating valve is increased, the system head pressure will also increase.
A.
True
B.
False
Q.47)
One large problem designer's face when designing air-cooled refrigeration and air conditioning equipment is a changing ambient from the changing seasons.
A.
True
B.
False
Q.48)
High head pressures from low ambients can cause insufficient refrigerant flow rates through metering devices, which in turn starve evaporators.
A.
True
B.
False
Q.49)
Low suction pressures, iced coils, short-cycling, and inefficient cooling can also result from low head pressures.
A.
True
B.
False
Q.50)
Hard starting may also occur in a low ambient conditions causing low head pressures.
A.
True
B. FalseA refrigeration system is operating with a vapor charged thermostatic expansion valve. The thermal bulb is sensing a suction line temperature that is higher than the temperature that allows liquid to be present in the bulb. Any additional increases in the evaporator load will ____.
A.
increase the bulb pressure and cause the thermostatic expansion valve to open
B.
increase the evaporator pressure and cause the thermostatic expansion valve to close
C.
decrease the spring pressure and cause the thermostatic expansion valve to open
D.
have no effect on the position of the needle (pin) in the seat
Q.2)
If a thermostatic expansion valve's thermal bulb came loose from the suction line at the outlet of the evaporator, which of the following could result?
A.
The bulb pressure would increase and the thermostatic expansion valve would open.
B.
The superheat in the evaporator would decrease.
C.
Liquid refrigerant would flow back to the compressor.
D.
All of the above are correct.
Q.3)
If the thermal bulb assembly develops a leak, what will occur?
A.
All of the system's refrigerant will leak out.
B.
The bulb pressure will reduce and the valve will close.
C.
The valve will open to allow more refrigerant to flow.
D.
It will have no effect on system operation.
Q.4 The purpose of an externally equalized thermostatic
) expansion valve is to ____.
A.
compensate for excessive evaporator pressure drop
B.
allow system to equalize faster
C.
prevent the expansion valve from frosting up
D.
allow refrigerant to expand in the compressor
Q.5)
The primary function of an expansion device is to ____.
A.
produce a reduction in the pressure on the liquid refrigerant
B.
regulate the flow of refrigerant into the evaporator
C.
lower the boiling point of the refrigerant far enough below the temperature of the load to get the needed heat transfer rate
D.
all of the above
Q.6)
A thermostatic expansion valve controls refrigerant flow to the evaporator based on ____.
A.
rate of liquid vaporization
B.
evaporator suction line superheat
C.
external equalizer pressure
D.
all of the above
Q.7)
The purpose of a capillary tube is to ____.
A.
regulate the refrigerant flow into the evaporator
B lower the pressure of the liquid
. refrigerant
C.
lower the boiling point of the refrigerant
D.
all of the above
Q.8)
The TXV sensing bulb is mounted ____.
A.
on the liquid line between the condenser and the TX valve
B.
at the inlet to the condenser
C.
on the suction line between the evaporator and the compressor
D.
on the compressor discharge line
Q.9)
When the load on the evaporator increases, the TX valve ____.
A.
increases the flow of refrigerant
B.
decreases the flow of refrigerant
C.
maintains constant head pressure
D.
decreases the pressure drop across the evaporator
Q.10)
The cross liquid charge bulb at the TXV contains fluid that ____.
A.
has similar characteristics to the system fluid to prevent liquid refrigerant from entering the suction line
B.
has different characteristics from the system fluid
C.
causes the valve to stay open during the off cycle
D.
follows the typical pressure-temperature relationship
Q.11)
Balanced port TX valves are used to ____.
A.
feed refrigerant at a normal rate with low condenser entering air temperatures
B.
feed refrigerant at a normal rate with high condenser entering air temperatures
C.
stop refrigerant flow with high condenser entering air temperatures
D.
stop refrigerant flow with low condenser entering air temperatures
Q.12)
The pressure limiting TX valve ____.
A.
allows the compressor to operate at low condenser entering air temperatures
B.
shuts off the condenser fan during hot pull down
C.
maintains the full refrigerant flow rate during a hot pull down
D.
limits the refrigerant flow rate to the compressor capacity
Q.13)
If the power element of a TX valve loses its charge, the ____.
A.
coil will flood enough to feed liquid refrigerant out of the coil
B.
valve will get cold enough to create frost on the body of the valve
C.
refrigerant flow through the various circuits of the coil will become unbalanced
D.
refrigerant flow to the coil will stop
Q.14)
A refrigeration system that continuously runs under high-load conditions (hot pull downs) would most likely use a thermostatic expansion valve with a vapor charged thermal bulb assembly.
A Tru
. e
B.
False
Q.15)
An automatic expansion valve uses a thermal bulb to help control the amount of refrigerant being fed into the evaporator.
A.
True
B.
False
Q.16)
A refrigeration system requiring a "fast pull down" would most likely use a thermostatic expansion valve with a liquid - thermal bulb.
A.
True
B.
False
Q.17)
The step-motor valve uses a small motor to control the valve's port, which in turn controls evaporator superheat.
A.
True
B.
False
Q.18)
A vapor-charged thermal bulb assembly responds faster than a liquid-charged thermal bulb assembly.
A.
True
B.
False
Q.19)
As the load on an evaporator increases, the automatic expansion valve will open to allow more refrigerant to enter the evaporator.
A.
True
B.
False
Q.20)
A capillary tube controls the refrigerant flow into the evaporator.
A.
True
B.
False
Q.21)
An AX valve works best when the evaporator load is constant.
A.
True
B.
False
Q.22)
The pin or valve port piston of the electronic step-motor expansion valve can move a linear motion of 0.0783 inches/step.
A.
True
B.
False
Q.23)
Too high of pressure entering the compressor will cause the density of suction gases entering the compressor to increase.
A.
True
B.
False
____ 1. If the compression ratio of a system with a reciprocating compressor decreases, the amount ofrefrigerant pumped by the compressor ____.a. will increaseb. will decreasec. will remain the samed. cannot be determined____ 2. If the suction valve in a reciprocating compressor is leaking slightly, the ____.a. cooling capacity will be reducedb. flow rate of refrigerant through the system will increasec. compressor can overheatd. both a and c____ 3. The clearance volume of a compressor ____.a. increases as the compression ratio increasesb. increases as the compression ratio decreasesc. decreases as the compression ratio increases
d. remains the same as the compression ration decreases____ 4. What could happen if a semi-hermetic compressor is operated with the suction service valvebackseated and the discharge valve frontseated?a. The system will pump down.b. The system will pump out.c. The head of the compressor may blow off.d. The compressor capacity will increase.____ 5. Liquid entering the compression chamber of a reciprocating compressor can lead to ____.a. damaged valvesb. damaged piston ringsc. damaged expansion valvesd. both a and b____ 6. Most of the heat energy in the suction vapor entering the compressor is ____.a. heat of compressionb. sensible heatc. latent heatd. defrost heat____ 7. The temperature of the compressed gas leaving the compressor can best be described as ____.a. coldb. coolc. warmd. hot____ 8. The screw-type compressor is used primarily in ____.a. large industrial refrigeration and air-conditioning systemsb. residential air conditioningc. small commercial refrigeration unitsd. domestic refrigerators____ 9. Rotary compressors are used primarily in ____.a. large industrial refrigeration and air conditioning systemsb. residential air conditioningc. small commercial refrigeration unitsd. domestic refrigerators____ 10. The clearance volume of a compressor cylinder is the ____.a. amount of refrigerant vapor the compressor cylinder will hold during each strokeb. volume by which the compressor is ratedc. volume of the space between the bottom of the valve plate and the top of thepiston at top dead-centerd. the total volume of the cylinder when the piston is at the bottom dead-center____ 11. The discus valve design is more efficient than a flapper valve design because ____.a. it allows a compressor design with less clearance volumeb. it operates with less spring tensionc. the amount of expanded vapor in the cylinder is greaterd. it will not allow liquid refrigerant in the cylinder____ 12. Which of the following terminal combinations would show an open circuit if the internal overloaddevice in a hermetic compressor should open due to excessive heat?a. common to startb. common to runc. start to rund. both a and bTrue/False
Indicate whether the statement is true or false.____ 13. The suction and discharge valves in a reciprocating compressor open and close depending on thedifference in pressure across them.____ 14. Scroll compressors are becoming popular because they can handle some liquid floodback withoutcompressor damage.____ 15. The scroll compressor is one type of reciprocating compressor.____ 16. Rotary compressors have pistons that rotate inside the cylinders.____ 17. Rotary compressors have no "clearance volume."____ 18. The sight glass on a semi-hermetic compressor is used to allow light to enter the crankcase to keepthe oil warm.____ 19. The shell of a hermetic type reciprocating compressor is in the low pressure side of the system.____ 20. The hermetic reciprocating compressor motor is essentially made of the same materials as an opentype compressor motor.____ 21. A bolted together motor-compressor assembly is sometimes referred to as a semi-hermetic type.____ 22. The higher the rpm of a compressor, the higher the pumping efficiency.