air conditioning system superheat

8/6/2019 Air Conditioning System Superheat

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Air Conditioning System Superheat & Subcooling Procedures forOptimal Charging

- with Darrell Udelhoven - HVAC RETIRED - * CustomersA SimpleA/C Check you can do!

Checking BTUH Performance of your Air Conditioner|* HEATPUMP DIAGNOSTICS

First, Anchor link, Determining which metering device TXV orFixed Orifice - without looking|SUBCOOLING|

WARNING: on units with a Thermostatic Expansion Valve (TXV), youcannot use the suction pressure to check the charge;many appear to be doing this; it tells you nothing. *Instructive HVACVideos at bottom of this page!

*Basics Featuring the Testo 556 - *Video of thorough requiredAir Conditioning BTUH Performance Test

Always begin with a thorough Home Energy AUDIT that shows allthe options for lowering the heat-gain & heat-loss, then afterreducing air infiltration, etc., have a room by room manual Jheatload calc performed. A reduction in equipment sizing willusually greatly improve the duct system performance.

This is where the greatest savings in both heating & cooling will

accrue; this will help in the down-sizing of equipment.

"The 'proper heatload' on the evaporator coil must be established"Check and thoroughly seal all the ductwork! For efficient operation,always check the return air temperature at the blower & at theReturn Air Grille(s) to know whether it is drawing hot air from theattic or garage areas.

What I stated above, that ought to be done is far more importantthan SEER rating; as the above will determine the SEER achieved &the energy savings.

Then do a manual J room by room heat-gain calc with the optionshown so you can do everything possible to reduce all sources ofheat-gain & heat-loss, greatly reducing both heat & cooling BTUHequipment sizing.

Before you do anything else, educate yourself enough to "ensurethat you request the proper things be done in the proper order of
http://www.udarrell.com/check_ac.htmlhttp://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html#Checking_BTUH_Performance%23Checking_BTUH_Performancehttp://www.udarrell.com/heat_pump_diagnostics.htmlhttp://www.udarrell.com/heat_pump_diagnostics.htmlhttp://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html#Determining_Metering_Device%23Determining_Metering_Devicehttp://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html#Determining_Metering_Device%23Determining_Metering_Devicehttp://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html#RHEEM_ENGINEER%23RHEEM_ENGINEERhttp://www.youtube.com/watch?v=2GjDgfCohcI&feature=mfu_in_order&list=ULhttp://www.udarrell.com/check_ac.htmlhttp://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html#Checking_BTUH_Performance%23Checking_BTUH_Performancehttp://www.udarrell.com/heat_pump_diagnostics.htmlhttp://www.udarrell.com/heat_pump_diagnostics.htmlhttp://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html#Determining_Metering_Device%23Determining_Metering_Devicehttp://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html#Determining_Metering_Device%23Determining_Metering_Devicehttp://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html#RHEEM_ENGINEER%23RHEEM_ENGINEERhttp://www.youtube.com/watch?v=2GjDgfCohcI&feature=mfu_in_order&list=UL


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sequence." Checking ductwork & Airflow Checking StaticPressures is Critically Important. As is knowing the operating feetper minute (FPM) velocity, the CFM & BTUH to each room along withthe Total CFM airflow & BTUH.

Only after you have verified that all the coils are clean & the airflow isright-on,can you begin to check the system's charge using Subcooling methodwith a Superheat check.Always check the actual airflow CFM 'before' checking thecharge, - get that Right First!

There is a local TXV 1.5-Ton system that has very low airflow, actuallyless than 200-cfm per-ton of cooling,they're only checking the suction pressure & saying the charge &everything is okay!

By the way, the furnace is a 112,000-btuh output & requires near1200-CFM; it is a CRIME to do such an A/C installation!

That system has a TXV & shows; 98-F condenser saturation temp & 97-F liquid line temp near E-Coil,a mere 1-F Subcooling, it's undercharged even with a mere 200-cfmper-ton cooling load! Unbelievable, - but it's happening out there!

Check the Superheat & the Subcooling as outlined below and alwayscompare to the charging instructions that are with the equipment as

some use theApproach Method & other methods may vary the operating figures & Target figures vary somewhat from Super Heat & Sub Coolingmethods!

Those varied methods will usually be close to Super-Heat (SH) & Sub-Cooling (SC) results. I would always use the SH & SCmethod in conjunction with the mfg'ers method to trouble shoot therefrigerant system.

Let's say with a TXV according to the Target Super Heat & your

collected data indicates a starved evaporator coil & a normal or slightlyoff Subcooling,even if you are using a Mfg'ers Approach Method do NOT automaticallybelieve that it is undercharged.

One company is reportedly having problems with TXVs starvingEvaporator Coils, or it could be a partially plugged TXV strainer/screenor other restriction.
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--------------------------------------------------------------------------------------------------------------A new easy to use Super Heat & Sub Cooling test instrument:http://www.ueitest.com/ssm1/

Optimize Evaporator BTU/hr Heat Input 1st always - "Optimizeevaporator airflow heatload."

To Determine Super Heat (SH):*** First, the airflow through the evaporator has to beabsolutely correct blower wheel blades & evaporator clean!

1. Take the Suction Saturation Temperature (SST) reading from yourmanifold gauge.

2. Then take the Suction Line Temperature (SLT) as close to thecondensing section just before the serve valve.

3. Take the difference between the above readings (Suction Line Temp'minus' Gauge Saturation temp reading) = Superheat

4. When ambient air temperature (Outside air temperature) is 85degrees or above the Superheat should be 8-12 degrees.Thermostatic Expansion Valves (TEV / TXV) should be set for aminimum 8-F Degrees Superheat.

Some Heat Pumps with TXV's are set at 7 to 9-F Super Heat becausethey have Suction Line Accumulators to store any spill-over liquid,which protects the compressor.

Superheat should be checked as close to the inlet of the evaporatorrefrigerant metering device as possible.

For TXV Subcooling, take the pressure of the liquid line notethe gauge saturation temperature.Compare it to the actual temperature obtained near the samepoint the pressure was obtained.

Thermostatic Expansion Valves (TEV / TXV) should be set for aminimum 10-Degrees Superheat on A/C systemsHeat pumps with accumulators down to 7-F Super Heat.

This linked page is strictly a SUPERHEAT TABLE Print theseTables & use them!

Print this Two linked pdf pages: Target Super Heat Chart and
http://www.ueitest.com/ssm1/http://www.udarrell.com/air-conditioning-efficiency-btuhr-evaporator-coil.htmlhttp://www.irrsupply.com/superheat_table.htmhttp://www.wifocusonenergy.com/data/common/dmsFiles/R_HC_GUID_Airflow%20and%20Refrigerant%20Tables.pdfhttp://www.ueitest.com/ssm1/http://www.udarrell.com/air-conditioning-efficiency-btuhr-evaporator-coil.htmlhttp://www.irrsupply.com/superheat_table.htmhttp://www.wifocusonenergy.com/data/common/dmsFiles/R_HC_GUID_Airflow%20and%20Refrigerant%20Tables.pdf


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this Target Temperature Split for Airflow Chart

Here is a formula for getting the Super Heat Target - Withinnormal perimeters:((IWB) Indoor Wet Bulb X's 3 - 80 - (OAT) Outdoor Ambient

Temp) / divided by 2 = Superheat Target

5. If Superheat is low then the evaporator is flooding. Note: Do NOTadjust charge YET.

6. If Superheat is high then the evaporator is starving. Note: Do NOTadjust charge YET!

7. Do not adjust charge UNTIL Sub-Cooling is checked.

Note: When charging a system using Superheat, you are charging

the unit to the amount of air (CFM) and total heat load that iscrossing the evaporator coil(Thus, the amount of latent and sensible heat load being absorbed bythe evaporator coil).

Note: Do not adjust charge based on Superheat on systems withThermal Expansion Valves (TXV, TEV's), (use Liquid Line Sub-Cooling.TEVs control the superheat; you should check the superheat to see ifthe TEV is working properly.Thermostatic Expansion Valves (TEV / TXV) should be set for aminimum 8-Degrees Super Heat.

To Determine Liquid Line Sub-Cooling (SC):*** First, the airflow through a clean evaporator has to beabsolutely checked as being correct!1. Take the high side pressure and convert it to temperature usingchart or gauge.

2. Then take the temperature of the liquid line as close to thecondenser as possible..

3. Take the difference between the above readings. (Saturation Temp

Liquid Line Temp.).Note: liquid line temperature at the evaporator should be within 2degrees of liquid line temperature at condensing unit.If not, could be a restriction or line set too long.

4. Sub-Cooling with a TXV, should be around 9 to 15-F degrees,always check with the mfgers for correct SC
http://www.wifocusonenergy.com/data/common/dmsFiles/R_HC_GUID_Airflow%20and%20Refrigerant%20Tables.pdfhttp://www.wifocusonenergy.com/data/common/dmsFiles/R_HC_GUID_Airflow%20and%20Refrigerant%20Tables.pdf


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5. Then using the information from Superheat and Sub-Cooling we canhave some idea where to look for a problem.Example:Suction Line Temp is ------- 60 degrees @ condenserGauge Suction Pressure is ------76-psig ---- 45 degrees, Read Gauge

Suction Saturation Temperature (SST)60 degrees 45 degrees = 15 degree Superheat - Adjust charge to themfg'ers Super Heat settings

Liquid Pressure is ------------226-psig --------110 degrees, Read Gauge -Liquid Saturation Temperature (LST)Liquid Line Temp (LLT) is -------------95 degrees110 degrees 95 degrees = 15 degree Sub-Cooling - AdjustRefrigerant charge to the mfg'ers SC settingsOn TXV metered systems the Subcooling should be within +/-2-F of the mfgers installation instructions.

==========================Air Conditioning Performance Diagnosis using listed (CT)Condensing Temperatures

Using Goodman 16-SEER "Expanded Performance Data"

Find the correct (CT) Condensing Temperature with thefollowing known mfgers data.

Outdoor Ambient Temp (OAT) 85-F; IDB 75-F; IWB 63-F or 50%-RH.

Listed pressure is 316-psig, or 99-F CT; that is 99-F -85-F is a14-F SPLIT.

The delta T or temp-split should be within a 10-psig range or,+/- 2-F degrees; 97 or 101-F.

The mfgers Supply Outlet should be able to provideContractors & Techs with those performance data charts.Goodman has their Expanded Performance Data on theInternet.(1) Get a low-cost digital flat-headed pocket Thermometer to

use flat on the piping;these test instruments will PAY big returns!

(2)Get a low cost Testo Tester & ballpark figure actual BTUH &EER - the information on it:http://www.amazon.com/Testo-605-H2-H.../dp/B000774B6A
http://www.amazon.com/Testo-605-H2-Humidity-Stick-bulb/dp/B000774B6Ahttp://www.amazon.com/Testo-605-H2-Humidity-Stick-bulb/dp/B000774B6A


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(3)Home owners; -a very low cost anemometer to get airflowFPM Velocities, I'd get it:http://www.amazon.com/Crosse-Technol.../dp/B0002WZRKE

Get a low cost Testo Tester & ballpark figure actual BTUH &EER - the information on it:http://www.amazon.com/Testo-605-H2-H.../dp/B000774B6A

Also, get a low-cost digital flat-headed pocket Thermometer touse flat on the piping; these test instruments will PAY bigreturns!-----------This should be helpful, as you can use this info to determinethe actual realtime BTUH output of your A/C system:

Take the Supply Air & Return Air wet bulb temperatures &interpose them on the enthalpy chart linked below.Duct system CFM X* 4.5 @sea-level, or use X* 4.35 if 1000'above sea-level,X* change in enthalpy = BTUH (Ballpark) OperatingPerformance."U Must Right Click Link & open in New Tab," look-up wet bulbenthalpy figures on chart," & figure enthalpy change.Wet Bulb Enthalpy Chart

Rules of Thumb for Duct Systems - Hart&Cooley

DESIGN AND INSTALLATION OF RESIDENTIAL FLEXIBLEDUCTWORK SYSTEMShttp://www.dca.state.ga.us/development/constructioncodes/publications/1ONE.pdf

Look at the ducting, if it is not to code; make hard copies ofthis code & give it to whoever does the ducting workMake sure they redo it right!Never have flex duct interiors commercially cleaned, I just viewedHome Inspection photos showing the interior damaged & insulationplugging the duct.

Home Inspectors warn people because the duct cleaner's tell them itwon't damage the ducts. Some HI's look into the boot areas for clues ofproblems...=============================================================------------------Identifying your registers/diffusers & their (Ak) sq.ft. area, so you canmultiply the FPM Velocity times the Ak to get the (CFM) Cubic Feet per
http://www.amazon.com/Crosse-Technology-EA-3010U-Handheld-Anemometer/dp/B0002WZRKEhttp://www.amazon.com/Testo-605-H2-Humidity-Stick-bulb/dp/B000774B6Ahttp://www.udarrell.com/wet_bulb_enthalpy_chart.pdfhttp://efficientcomfort.net/ToChart4.htmlhttp://www.dca.state.ga.us/development/constructioncodes/publications/1ONE.pdfhttp://www.dca.state.ga.us/development/constructioncodes/publications/1ONE.pdfhttp://www.amazon.com/Crosse-Technology-EA-3010U-Handheld-Anemometer/dp/B0002WZRKEhttp://www.amazon.com/Testo-605-H2-Humidity-Stick-bulb/dp/B000774B6Ahttp://www.udarrell.com/wet_bulb_enthalpy_chart.pdfhttp://efficientcomfort.net/ToChart4.htmlhttp://www.dca.state.ga.us/development/constructioncodes/publications/1ONE.pdfhttp://www.dca.state.ga.us/development/constructioncodes/publications/1ONE.pdf


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Minute airflow from that register.Have or do a manual J heat-gain calc for each room. If a room calls for3,000-BTUH; first divide 12,000-BTUH by the CFM PER TON you want touse.

I.E., Wet coil, 12,000/400=30-BTUH per each CFM; Wet coil12,000/425=28.235294; 3000/28.235-= 106.25-CFM;Dry coil, 12,000/450= 26.6666-BTUH; 3500 / 26.6666= 131.25-CFMIf register/diffuser has the same (Ak) free-airflow-area, as the duct run!

Room calls for 3,500-BTUH, using 450-cfm per/ton dry coil or 26.6666-BTUH per CFM= 131.25-CFM.I.E., 6" rd duct .6*6=36*.7854=28.2744sq.ins/144=0.19635-sq.ft.;131.25-cfm / 0.19635-sq.ft= or 668.4-fpm velocity.

SP2 = (rpm2/rpm 1)2 X SP1 = SP2

Required fan motor horsepower (hp) varies as to the cube of the rpmspeed:

hp2 = (rpm2/rpm1)3 x hp1 = hp2

CFM Fan delivery varies directly as to the fan RPM speed:

cfm2 = (rpm2/rpm1) X cfm1 = cfm2

Duct retro-work can solve the problem, increasing blower HP alonewon't usually work!A few calculations plus retro-workand presto, a matched airflow withyour systems' heat absorbing coil capacities,delivering near its BTUH, EER, and SEER ratings at normal roomtemperature settings! (Most don't)

==========================================

============*You could ballpark the CFM using the static test & a air handler graph.You could measure the CFM delivered to each room with a hood AlnorBalometer,it's usually the best instrument to use, but not cheap. Measuring theair velocity is a bit tricky because you have to use the diffuser datawhich you don't always have available.


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A rough ballpark formula to get the CFM: CFM = (velocity in (FPM) Feetper Minute times the square footage of the duct area, you have tohave & use the diffuser data & get velocity there -for operatingconditions.) Taking the manifold gage head pressure & gagecondensing temp, is important data. Coupled with a TH condenser

temp-reading, if the condenser gage pres/temp is too highcompared to the TH reading, there may be non-condensibles inthe system.

Also, there is a legitimate formula I use to determine theoperating BTUH it is delivering at all the data taken. All themfg'ers ought to list the condenser temp-split (it varies withEER & SEER) just like they list the indoor split, it is valuabletrouble shooting info.

You can also use the condenser temp-split (it contains both Latent &

sensible heat) combined with the indoor data to plot the indoor CFM. Iwas never good at math, but those equations have to balance, & theydo work!==================The A/C user need not know all the tech info, all they need to know area very few basic ways to identify that the system is not functioningcorrectly so they can call for a pro-tech to properly trouble shootthe system.

Now the reality is that you don't need a manifold gauge, - anyone canBallpark check the charge in respect to the indoor airflow with only a

little low cost MA-Line digital thermometer using some tubinginsulation on the sensor probe.http://www.ma-line.com/HTML/L1_productmenu.htmlYou can't order it there.

However First, you check the discharge air temp off the outdoorcondenser, (that is the "Condensing Temperature (CT)," the higher theSEER Rating the lower the outdoor normal temp/split above theoutdoor temperature will be.)Then you either check the small liquid line tubing temp outdoors wherethere is a tubing bend, or indoors where it bends to enter the plenum.

Indoors could be inaccurate as the tubing temp could vary higher orlower depending on temp conditions the line is conducting.

Subtract the small liquid line temp from the CT & you have theSubcooling temp which varies some from mfg'ers, but will be Ballparke8 to 12-F Subcooled.
http://www.ma-line.com/HTML/L1_productmenu.htmlhttp://www.ma-line.com/HTML/L1_productmenu.html


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The condenser temp (CT) above the outdoor temp tells you how muchindoor sensible & latent heat, & the 3 motor heats it is ejecting. Theindoor humidity level has the biggest effect, the higher the humiditythe hight the split.

Now, indoors the higher the humidity the lower the temp/split betweenSupply-Air & Return-Air.

At 50% indoor humidity the split should be Ballpark, around 18 - 20-F.

If blower wheel blades & all coils are relatively clean & the split is wellabove 20-F, you have low airflow with a low heatload through theevaporator coil.

If the indoor split is way below 18-F at 50% RH, you either have waytoo much airflow or some problems in the functioning refrigerant

system.

To solve any of these problems you need to call aknowledgeable HVAC TECH! - Darrell U-------------------------- An Affordable Test Instrument You Need!All I had was the Sling Psychrometer & spinning it was a bit timeconsuming, but I used it religiously, it is information you need.

The Testo 605-H2 Humidity Stick (wet bulb), displays relativehumidity, air temperature and wet bulb temperature.

It is very affordable & because of its potential to help deliver tons ofother data everyone should have one!

For more information on it:http://www.amazon.com/Testo-605-H2-H.../dp/B000774B6A

The other test data you need is the system's CFM airflow through theevaporator coil, then with software I have you can peg the BTUH theoperating unit is delivering under those conditions.Add to that a low cost Magnehelic gauge to read static pressures to

compare with mfg'ers blower performance charts; plus a velocitymeter & you have a ballparked CFM to plug into for the BTUH.

We could easily provide a detailed psychrometric print out ofexactly what the operating system is delivering includingcondensate lbs/hr, & actual sensible & latent cooling BTUH &Ratio, every data detail imaginable.============================
http://www.amazon.com/Testo-605-H2-Humidity-Stick-bulb/dp/B000774B6Ahttp://www.amazon.com/Testo-605-H2-Humidity-Stick-bulb/dp/B000774B6A


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It is important to understand that "equipment ratings are only the'potential efficiency' of that component of the system under perfectconditions." Over half of the systems efficiency depends oncorrect equipment sizing run-time, on the duct system sizing,i.e., on the quality of the complete field-installation!

Especially if your system is oversized or there are a lot of low AC loaddays use an adjustable differential room TH.TH Differential: Differential is defined as the difference between thecut-in and cut-out points as measured at the thermostat underspecified operating conditions. For example, if the thermostat turns theCOOLING EQUIPMENT on at 78-F & OFF at 76-F that is a 2 degreedifferential setting; one has a 4-F adjustable differential. This is a goodway to control high humidity problems & also improve SEERperformance.

What you want & need is right sized equipment operating atits optimal ratings within varying conditions, for your optimalcomfort and savings.

*CONDENSING TEMP CT Diagnosis*

| Lennox TXV Subcooling Approach | | R410a Evacuation |Differential RM T- statImproves SEER |*** Sizing Units toAdequate AirflowNew

CHECK RETURN AIR for HOT AIR LEAKS | Gurgling sounds atTEV | Trouble Shooting TXV Valves |Affordable TestInstrument You Need

The duct system airflow must be checked & correct, beforeperforming any charging procedures!My ordered procedure that must be followed to achieve anoptimally charged efficient operating air conditioner.Do not leave out any of the steps and always do theseprocedures in the order sequence illustrated.

First, check that there are NO air leaks in the Supply and Return Airduct system.Next, Check to see if Indoor Squirrel Cage Blower wheel blades are freeof lint or other build-up & Filter.Before checking the refrigerant charge always check the actualair flow with an anemometer & apply the math shown below!

Check for a dirty lint clogged Evaporator Coil fins then check the
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Condenser Coil fins, check both coils on the air entering sides as wellas between the fins, -- clean if needed.

Take a look at the ductwork for proper sizing and for leaks, Check theExternal Static Pressure (ESP),check the indoor Cubic Feet per

Minute (CFM) Airflow, then outdoor condenser discharge airTemperature split (delta-T), then indoor Delta-T, then after 15 minutesof run time before any charging adjustments are made. On smallertonnage equipment & in most climates that are not overly humid, I like425 to 450-CFM per/ton of cooling on a wet coil.

In summer, Air conditioner & heat pump user's, this is a "Simple EasySafe Way" to Check an A/C's Thermostatic Expansion Valve(TXV) metering system's refrigerant charge & any A/C'sPerformance:Record the outdoor temperature, then "Take a thermometer &

check the air temperature coming off the outdoor condenser."

Locate the small uninsulated copper line where it makes a bend,outdoors or indoors, so you can put a digital thermometer flat on it &insulate the TH with something (piece of the tubing insulation) read thetemperature & subtract it from the outdoor condenser discharge airtemp.

E.g., condenser temp 110, line temp 100-F that is 10-F subcooling & 10to 12-F is a normally charge system. If it's considerably less than 10-Fit could be low on refrigerant or need a Tech to check it; too far above

12-F it's overcharged, call a Tech, could also be a restriction in thelines.

You should own a low cost digital pocket thermometer: Now the realityis thatyou don't need a manifold gauge, - anyone can Ballparkcheck the charge in respect to the indoor airflow with only a little lowcost MA-Line digital thermometer using some tubing insulation on thesensor probe. An A/C supply Outlet might sell you one or inquire athardware stores! Saves money on needless A/C Service Calls!http://www.ma-line.com/HTML/L1_productmenu.html

Take the outdoor temperature & subtract it from the outdoorcondenser's discharge air temperature.This temperature is standard for different SEER Rated units.

A 12-SEER unit, with 50% relative humidity indoors will haveballpark, will have an 18 to 20-F temp splitA 14-SEER will be around a 14 to 16-F temp/split. if too farabove or below those temps, call for an A/C Tech.
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Formula for finding CFM AirflowIf you can measure the air velocity coming from a duct, here is a roughballpark formula to get the CFM:CFM = (velocity in (FPM) Feet per Minute times the square footage of

the duct area)Example, 16" Rd duct 201-sq.ins. X's 0.00694 = 1.39494-sq.ft. X'sVelocity of 800-fpm = 1,116-CFMTimes 1000-FPM = 1395-CFM.Branch ducts: 7" Rd duct 38.48-sq. ins. X's 0.00694 = 0.2670512-sq.ft.X's 500-fpm=133.5-cfmHowever, times a velocity of 600-FPM X's 0.00694 = 160-CFM, thevelocity is a big room CFM & BTUH number changer.-----------------------------------------------------------------------Quick Check for Sizing Units to enough AirflowActually, even on service calls where there are cooling problems the

ductwork should have a quick Manual D performed.

Take the ESP static pressure & compare to blower graph or chart, alsotake the FPM duct velocity.For Room Return Air balancing, i.e., -.01" IWC = approximately-2.48 Pascals, which is a more precise easier incremental scale toread.One inch water column (IWC) equals rounded to > 250 pascals,0.5" IWC is about 125 pascals; 0.25" WC = 62.5 pascals; 0.125 =31.25 pa.;1 / 250 pascals =0.0040322 *X's -2.50pascals =

-0.01003657696655" IWC or make it - 0.01" IWC for low Return Airroom pressure differentials; - use pascals.

Here are some examples of residential or light commercial in InchesWater Column (IWC) Pressure Drops. Check the engineering data asyou design, and you may be surprised.This is mainly only the example of the Device pressure losses.

Then do a quick estimate ofairflow per equipment tonnage.To find area of a round duct; Duct diam is 7"; 7"X7"= 49-sq.ins., X's .7854 = 38.04845-sq.ins divided/ by 144= 0.2672541-sq.ft. area X's

FPM Velocity 600-FPM =160.35246-CFM X30 = 4,810.5738 each 7" run X's 6 branch runs =28,863-BTUH, or airflow for 2.4-ton.(12,000-BTUH /400-cfm per-ton = 30-BTU per cfm ratio | / 450 =26.666-BTUH per-cfm)

That would also be good for 2-ton; at 550-FPM velocity X's 0.2672541=147-CFM X 30 = 4,410-BTUH each run X 6-runs = airflow for 26,460-


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BTUH.

*Never sell units requiring more airflow than the duct systemwill support! - Darrell udarrell

====================================================

TROUBLE SHOOTING TXV VALVE SYSTEMS

Bulb location: Some Mfgs have there preferences, but a good rule ofthumb is 10 or 2 OClock, away from headers and heat exchangers, ona smooth clean surface.

Also, make sure the cap tube is on top (horizontal or vertical and

never upside down).

Pressure drop: TXVs like to have at least 100-psi pressure dropacross them to operate correctly.A solid column of liquid (atthe valve) is also a requirement.

Flood back: Always make sure you have "the correct CFM airflow"(clean coils,"Clean fan blades & fans running on correct speeds and in theright direction) before you try adjusting a valve.

No flow: A plugged screen is rare in air conditioning, but happensoften in refrigeration.I have seen the external equalizer tube leak through in liquidform and give the bulb a false reading (which causes huntingmore so than no flow).-------------------------------TXV Partially plugged, downstream from service port, filter-dryer or screen at Compressor Inlet,therefore TXV is Wide Open flashing some vapor & cooling coilis starved of liquid refrigerant:

In HVAC-TALK These Posts Illustrate and Discuss these TestResults

Lennox TXV Subcooling - Approach Method - pdf P- 8http://www.davelennox.com/pdfs/installation_maintenance/Lennox-12ACB-IOM.pdf
http://hvac-talk.com/vbb/showthread.php?p=1595389#post1595389http://hvac-talk.com/vbb/showthread.php?p=1595389#post1595389http://www.davelennox.com/pdfs/installation_maintenance/Lennox-12ACB-IOM.pdfhttp://www.davelennox.com/pdfs/installation_maintenance/Lennox-12ACB-IOM.pdfhttp://hvac-talk.com/vbb/showthread.php?p=1595389#post1595389http://hvac-talk.com/vbb/showthread.php?p=1595389#post1595389http://www.davelennox.com/pdfs/installation_maintenance/Lennox-12ACB-IOM.pdfhttp://www.davelennox.com/pdfs/installation_maintenance/Lennox-12ACB-IOM.pdf


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Always check both SH & SC for trouble shooting comparison to normalparameters!---------------------There is a concern that we need more accurate means to achieve anaccurate target sub-cooling temperature under varying conditions.

First, before any operating performance feedback data is recorded,the following tests & corrections must be performed. We need tomake certain that the airflow is checked to be within the properparameters and that the ductwork is properly sized and sealed withreturn air grilles in every room at the ceiling level. In addition, ifpossible for the cooling mode, Supply Air Diffusers should also beat the ceiling level.

Accurate tests should also be made, to determine whether properairflow CFM is being delivered, as well as into each room.

The manufacturers could be of great help in this respect, if theywould list the Delta-T of the condensing unit at different BTUH loadoutput levels, also at various outdoor ambient temperatures.

I believe that with adequate test data feedback the subcoolingcould be targeted within plus or minus 1 or 2 degrees Fahrenheit,which would be a two to four degree differential.

That would be more accurate & concise a temperature target thanpresent subcooling temperature targeting methodologies.

Additionally, I would consider using the Lennox ApproachMethod to help select the Subcooling Method.

The Lennox Approach Method subtracts the Outdoor AmbientTemperature from the Liquid Line Temperature (LLT), whereas, thesubcooling temperature targeting method subtracts the Liquid LineTemperature near the evaporator from the Condenser SaturationTemperature (CST). I do not see why the Lennox Approach Method

would not help pinpoint the subcooling target on other systems.The Indoor Heatload has to be part of the equation; there are otherfactors to incorporate as well.

Possible Diagnosis using Super-Heat and Sub-Cooling:If Superheat is high and Sub-Cooling is low:Charge must be adjusted. System is Undercharged.


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If superheat is low and sub-cooling is high:Charge must be adjusted. System is Overcharged.

If Superheat is very high and Sub-Cooling is a little high:Could have blockage in coil, TXV strainer screen - settings, etc.,

orifice, filter dryers etc.

If Super-Heat is low and Sub-Cooling is low:Piston orifice could be too big, or some, in backwards, there is noorifice in the unit or the orifice is stuck and refrigerant is bypassingit.

To Determine Delta T (Td) (Temperature difference across thecoil):1. While unit is running take the temperature of the air in thesupply plenum near the coil (approx. 12 inches.)

2. Then, while the unit is still running, take the temperature of theair in the return plenum near the unit.3. Then take the difference between the above readings.4. Should be around 15-18 degrees. Use linked Chart above!5. If to low then coil might not be seated in pan correctly - airbypassing cooling coil. (Assuming superheat and Sub-Cooling areOK.)6. A TXV's normal Superheat setting is 12-F, between 7-F to9-F on heat pumps with an accumulator. There must be afull liquid stream to the TXV!

With a TXV metering device ifSuperheat is too high say, 20-For above look for, suction line restriction, plugged captube/orifice./liquid line, hot gas discharge line restriction, filterdyer, downstream of suction service port, or compressor screenrestriction or inefficient compressor.-------What are the proper methods to determine operating superheat,sub-cooling?

Superheat at the evaporator should be checked as close to the endof the coil as possible (preferably near the expansion valve thermal

bulb). Convert this to saturation temperature and compare it to theactual temperature obtained near the thermal bulb. Take thesuction pressure at the service valve and convert it to saturationtemperature. Compare this to the actual temperature obtainedapproximately six inches out on the suction line.

Subcooling should be checked as close to the condenser aspossible & then as close to the TXV as possible noting the


16/20

difference.============With a TXV metering device ifSuperheat is too high say, 20-For above look for, suction line restriction, plugged captube/orifice./liquid line, hot gas discharge line restriction, filter

dyer, downstream of suction service port, or compressor screenrestriction or inefficient compressor.-------What are the proper methods to determine operating superheat,sub-cooling?

Superheat at the evaporator should be checked as close to the endof the coil as possible (preferably near the expansion valve thermalbulb). Convert this to saturation temperature and compare it to theactual temperature obtained near the thermal bulb. Take thesuction pressure at the service valve and convert it to saturation

temperature. Compare this to the actual temperature obtainedapproximately six inches out on the suction line.

Subcooling should be checked as close to the condenser aspossible & then as close to the TXV as possible noting thedifference.============

Determining which metering device TXV or Fixed Orifice thesystem has without physically looking

If you do not absolutely know whether the metering device is a TXV, or a fixed orifice device or cap tube.

Hook up your manifold gauges, block off considerable condenserair intake for a short time.If suction pressure changes it's a fixed piston or cap tubeIf only the high-side goes up, you have a TXV.

Have things with you in your van or truck to block-off thecondenser air for a short time.Check every time you are not certain what metering device it has.

There may be a lot of guessing in the future.

Do this procedure on known metering devices to observe thedifference.Report back to me how well it works for you.

In some situations, that could save you from cutting a hole in theplenum.


17/20

Squirrel cage wheels with forward curved blades on residentialsystemsunload when discharge air is blocked off too much & will overloadwhen there is no static pressure.

There is a preferable ESP range for each Air Handler blower design,that ought to be listed on the blower; they vary at the point ofserious unloading.If you amp-probe check enough of those blower motors, if the ampdraw is too low according to its rating, you can begin to tell thatthe External Static Pressures (ESP) is too high.Additionally, mfg'ers could list the amp draw at various design ESPnumbers, then we could amp-probe & know if it was too far abovethe amp rating, a duct maybe off,if amp reading is too low, it is time to check all static pressures &

delivered CFM to each room.

I lot of us used to set a nearly empty R-22 cylinder on top of acondenser to warm it a little. Back then fan motors had more HP& higher amp draws, therefore it didn't seem to cause any harm, just more noise.

Back in the 1960's & 1970's there were a fair number of TXVmetering devices & some table top condensers' that had the fanunderneath blowing up through the coils.Well, where there were cottonwood trees, nearby clothes dryer lint

vents, or a lot of leaves or other debris under the unit, the fanmotors would be blocked overload & burnout.

I don't understand the engineering genius of that moronic design.

However, on hot days & a heat-loaded E-Coil,You could move your wrist over the condenser from outlet up toinlet, & tell if the liquid was taking up too much area of the coils;an overcharged system. - udarrellGurgling sounds at TEV: Low evaporator heat-loads lead toreduced liquid line mass and increased evaporator mass could be

due to airflow problems. Eliminate low evaporator heat-loadsbefore looking into adjusting the refrigerant charge. Gurgling -pulsation noises in Liquid Line at the expansion device canbe caused by low evaporator circuit heat-loads, low charge,and/or non-condensibles and moisture in the system.Unbalanced airflow through the various distributor circuits of theevaporator coil will cause the TEV to close down refrigerant flowstarving the coil. Piston-flow-rators will make it impossible to


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properly charge the system and cooling will be greatlycompromised unless you eliminate the cause! "Put your ear on theliquid line at the evaporator coil."

On every Rheem condenser cover it lists "non-condensibles

and or moisture" as causes for a gurgling or pulsating noiseat the expansion device. The entire evaporator circuits,may not become active for various reasons, - "the entirecoil must become fully active for efficient performance."

The purpose of these recommendations is to provide liquidrefrigerant at the expansion device and provide efficient operation.Hopefully, this will aid your research. If I can be of additionalassistance, contact me.===============================================================

Check Return Air (RA) at grille & at entry of blower for heatgain, due to hot Return Air leaks.Where airhandlers' set over Return Air Chambers check forair leaks through the sheet rock & down the wall studsfrom the attic - this is a fairly common condition that willoverload the AC system!

DISCLAIMER:Any of the HVAC companies I list on any of my web pages havenothing to do with the information I post on any of my Web pagesnor do I assume any responsibility for how anyone uses that

information.All HVAC/R work should always be done by a licensed Contractor! This information is only placed on these pages for yourunderstanding & communication with contractors & techs.

This information is for the edification of contractors and techs. I amNOT liable for your screw-ups, you are liable for what you do! -Darrell Udelhoven (U-dl-hoven)

Darrell's Refrigeration Heating and Air Conditioning - Federalerant Licensed - Retired HVAC Contractor

Suction Low-SideSuction-PSIG -Normal to High

SUCTIONSuper-Heat -

HIGH

High-SideHead-Pres. -

LOW

Liquid-LineSUB-Cooling -

NORMAL

Cond.-UniAmp-Draw

LOW

ac-trouble-shooting-chart.html NEW! I'm finally posting these two pages I c TXV THERMOSTATIC EXPANSION VALVE APPLICATIONS - Important
http://www.udarrell.com/ac-trouble-shooting-chart.htmlhttp://www.udarrell.com/ac-trouble-shooting-chart.htmlhttp://www.udarrell.com/txv_applications_subcooling_superheat.htmlhttp://www.udarrell.com/ac-trouble-shooting-chart.htmlhttp://www.udarrell.com/txv_applications_subcooling_superheat.html


19/20

The Air Side of Air Conditioning - Static Pressure

AIR-CONDITIONER RUNNING TOO MUCH3.5-ton matched AC system getting only 1.25-ton of capacity! Low

Link below, 3.5-ton to less than 1.5-ton, too! - Way Overcharged

Air Conditioning SEER & Capacity Levels - Are you losing 15 to 50%

Optimizing the Evaporator BTU/hr Heat InputImportant - Do First !

Determining Your Air Conditioner's Actual BTUH Capacity Output

Air Conditioning EER - BTUH Levels - Evaporator (DX) Heat Load + Evap

Proper Sizing of Residential Heating & Air Conditioning Equipment and Air Conditioning Engineered for Latent Heat Removal For high humidity

Air Conditioning Contractors Discussion Sizing SEER EER Latent Heat An Air Conditioning and Heating Efficiency Check Up - Contractor

Air Conditioning System Sizing for Optimal Efficiency

Air Conditioning Maximum Efficiency - Check-Up Get your A/C optimized fo

Air Conditioning - Latent Heat Removal Comfort-Zone Efficiency

FINDING the LATENT HEAT of CONDENSATION of Your Air Conditioner

Optimizing Room Air Conditioner's EER

OIL HEATING AIRFLOW TEST Using Thermometers

Follow me on Twitter All about Reducing Energy Costs - New

Cut Your Home Energy Use & Utiliy Bills in HalfNew

HVAC Talk Community
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20/20

HVACR TALK FORUM - Residential Problems - NEW

Refrigeration Engineer Forums - AIR CONDITIONINGHOME INSPECTIONS Learn about home inspections also HVAC inspectio

DIY Do It Yourself Forum" "Do It Yourself" TV- I Am "HVAC RETIRED"MY HVAC BLOG - YOUR QUESTIONS & COMMENTS WELCOME*Use for listiGARDEN WEB - Heating & Air Conditioning ForumHVAC Discussions Mike Holmes HVAC Forum - New

Cynergy Home HVAC Energy RatersListen While Read

MY HVAC BLOG - YOUR QUESTIONS & COMMENTS WELCOMEUse for Data

Home Inspection - HVAC Easy checking of BTUH cooling performance...

*Video Checking Static - ESP| *Video 2 checking static - ESPView! Got D

Air Flow CFM of a very large Supply Air Register using a Testo 410 Vane

*Video measuring airflow Velocity W/ anemometer on a Return Air grilleI'd use close to .50% for the free-area of a clean FILTER, & .90% factor fHe programmed it in, because when I did the math using .90% for the gCFM, or 2-Ton of airflow.
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