Refrigeration gauge set (C) D FriedmanRefrigeration Gas Test Gauge FAQs

  • REFRIGERANT TEST GAUGE FAQs - CONTENTS: questions & answers about refrigerant test gauge use, connections, ports, & about refrigeration gas pressure measurement using a test gauge set.
  • POST a QUESTION or READ FAQs about how to hook up and use an air conditioner, heat pump, or other refrigeration equipment refrigerant gas pressure test gauge
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Air conditioner & heat pump refrigerant test gauge Questions & Answers:

Frequently-asked questions & answers about using a refrigerant test gauge set: connections, charging, pressures.

This article series describes the connections, use, and reading of a refrigerant gas pressure test gauge set.

We explain how a refrigeration gauge set should be connected to HVAC equipment to avoid contamination damage and we review the refrigeration system evacuation and cleaning procedure.

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Refrigeration Charging / Testing Gauge FAQs

R-22 refrigerant and air conditioning test gauges (C) Daniel Friedman

Recent questions & answers about refrigerant test gauge use, connections, charging ports, posted originally at GAUGE, REFRIGERATION PRESSURE TEST

On 2017-04-07 20:23:41.523418 by (mod) re: using the process port on an HVACR compressor motor


to have space and to cite authoritative sources (compressor motor manufacturers) I have moved our discussion and links to some PDFs into the bottom of the article at GAUGE, REFRIGERATION PRESSURE TEST - though it may take a few hours for the updated page to appear online.

On 2017-04-07 05:43:58.160911 by John

Thanks danjoefriedman, I check somewhere else and it tells me that the port I was talking about is a process port. There is the suction and discharge line, but this particular one says it's a process port. What worries me is the uncertainty of this process port. if it is on the low or high side of the compressor.

On 2016-12-30 22:35:38.924965 by (mod) re: bad heating element on a frost-free refrigerator


Your suggestion sounds perfectly reasonable, though the idea turns out to be more of a challenge than one might imagine.

A/C and heat pump equipment does not consume refrigerant. The system is hermetically sealed and the same refrigerant should stay in the equipment for its lifetime, barring mechanical damage that causes a leak. So we're not looking for something like a fuel tank gauge that's found on a car.

Your comment on frost-free equipment is spot on. Heaters keep frost-prone surfaces such around a freezer door or on the freezer internal surfaces either warm enough to not form frost/ice OR a timer periodically runs a de-frost cycle. In the latter case on older refrigerators you'll find a drain into a pan below the refrigerator/freezer. The pan catches the meltwater and lets it slowly evaporate into the environment.

If you disconnect just one heater element, say for a door, the unit may still have its internal defrost cycle working.

On 2016-12-30 21:47:10.741357 by ALVIS JENKINS

Actually I have a question. I have been told that a frost free refrigerator is frost free because of a heating element used to melt ice on the evaporator in the freezer compartment. Well, my frost free refrigerator is still frost free because my heating element went bad and I disconnected it. If you know how a frost free refrigerator works, please enlighten me. Thanks.

On 2016-12-30 21:42:00.942996 by ALVIS JENKINS

Wouldn't it be nice if AC Heat Pumps exhibited a readout of the unit when it runs low of gas so that owner can get adequate service before complete failure?

On 2016-08-16 21:37:44.294439 by (mod)

Thanks NJ Snowman, I've edited your remark and an appropriate warning into two places in the article above. - Mod

On 2016-08-16 20:32:10.904856 by njSnowman

In the section Guide to Refrigeration Gas Test Gauge Use you show a hand drawn schematic of the test gauge set.

According to what I see if both valves (the silver knobs) are opened simultaneously the Low Side and High Side will be connected directly together. In other words all three connecting hoses are connected together via the test gauge manifold.
I think a clear warning should be spelled out against opening both valves at the same time.

On 2015-12-14 09:41:04.116077 by suraj

Y refrigerator both tune gets ice

On 2015-10-29 14:34:19.929772 by Ravi Sharma

Please help me about how to read gauge value in empty compressor on mini refrigerator


(Oct 10, 2012) Adalberto Arroyo said:
this page is the best have to much information verry good.

(Mar 26, 2014) Jezoar said:
Thanks guys! This was great! Keep up the good work.

Question: what is a good R14 refrigeration pressure ? What should the refrigerant pressure be in my unit?

model cxa6 keeprite unit r14 refrigeration what psi pressure it should be good. - Litt 7/26/2011

what are the low and high readings for a 7.5 ton, 220 three phase compressor with two cooling coils and serves two inside units, mod BTA090C300H0, SER W01 195521 - 8/2/11



The pressure of any refrigerant will measure very differently depending on system operating status. At equalization pressure the LOW and HIGH sides will read the same, and as long as there is at least some liquid refrigerant in the system the pressure will be given by a temperature/pressure chart for that specific refrigerant.

If you scroll down to the list of article references below you'll see a link to a refrigeration pressure and temperature chart provided by Reece, an Australian company. That chart is missing R-14 refrigerant but at encyclopedia
[dot]airliquide[dot]com[slash]Encyclopedia[dot]asp?GasID=61#VaporPressureGraph you can find that information.

You'll see that at 10 bars of pressure R14 will be at 185K or about -88 C - in other words readily boiling to a vapor at ambient pressures. At 40 bars the temperature will be 230K or -43C. For a working pressure/temperature chart for refrigerants at ambient and typical HVAC pressures I'd go to the unit manufacturer.

[dot]airliquide[dot]com[slash]Encyclopedia[dot]asp?GasID=61#VaporPressureGraph you can find that information.

I add that for R14, its Latent heat of vaporization (1.013 bar at boiling point) is 135.7 kJ/kg

One Bar is 0.06895 psi
One kJ/kg = 2.326 British BTUs/Lb

But I THINK that the question you are asking is what pressures will be seen on the HIGH and LOW sides of a refrigeration system using R14 refrigerant.
For any refrigerant, you have to consult the individual refrigerant pressure/temperature chart, note the temperature of your system and the measured HVAC-system running stable state suction pressure (LOW SIDE) evaporative data, and of course the running HIGH side for the compressor/condenser condensation pressure data.

Mr. Cannon

You need to consul the manufacturer's technical literature for the refrigerant gas in use and the compressor model in use, and then you'll need to use a table of gases that provides temperature and pressure data in one place, as ambient temperature affects the answer. In sum there is no single precise right number. There are typical operating ranges of refrigerant pressures, as you can see a REFRIGERANT PRESSURE READINGS & CHARTS. Also take a look at our answer to Mr. Litt, just above.

Question: what causes excessive refrigerant pressure?

what cause to much high pressure - Anonymouse


Anon: among the reasons for excessively high pressure on the HIGH Side or output side of the compressor/condenser section of an air conditioner or heat pump are a plugged or debris blocked condensing coil, plugged refrigerant line, plugged dryer/filter on the line, or a stuck refrigerant metering device such as a capillary tube or thermostatic expansion valve.

There may be other causes of high refrigerant pressure that other readers can add.

Question: High pressure readings on the low side of my heat pump

I am getting very high pressure readings on the low side of my heat pump. The discharge and return line to the air handler are cool and equal in temp.(showing no refrigerant movement), But my suction line and discharge line leading in to and out of my compressor are very hot.

Have open the lines and checked the orifices and they are clear as is the lines to the air handler. Is it possible that the condensing alone can be clogged? I did have a compressor burn out last year. - D. Nix 8/7/11


High pressure on the low side sounds to me as if a metering device is stuck wide open; perhaps when your compressor burned up last year it left some debris in the refrigerant lines that has found its way to the TEV and has jammed it. Ask your HVAC tech to check the system again, check the TEV adjustment, and also consider installing a (new) filter/drier on both ends of the refrigerant piping system.

Question: can a refrigerant gas leak be fixed or does the whole compressor need replacement?

I need to know whether a leak form one of the compressor tubes is fixable or not. My technician said that the whole compressor would need to be replaced. - Ehab 8/176/11


Ehab refrigerant leaks can be repaired by various patch methods. But if the leak is discovered to be a symptom of more extensive corrosion, such as at a cooling coil, it's a much bigger repair than just a patch.

I'm not sure why, if the compressor was working normally, you'd need to replace all the equipment- perhaps the tech is referring to the issue that s/he cannot any longer recharge with R12 or R22 - used in older compressors, but there are alternative refrigerants that can often work with some adjustments.

Question: Comment on hose color coding; How do I know if the HVAC Tech Put In Enough Refrigerant?

Blue line goes to bigger line in compressor and red on little line
For high side - Anon 10/6/11

Hello, For a typical home split air conditioner, how to make sure that the technician has filled in enough gas in the out door compressor unit? - Sanjay 7/21/2012


Sanjay, without evacuating the air conditioner completely and putting in a precisely measured charge using gauges and metering equipment, you cannot know yourself exactly how much refrigerant is in the system. But there are indications of the refrigerant charge being too much or too little that can show up without sophisticated instruments. For example:

- if you hear a bubbling sound in the liquid line the charge may be low

- if you see bubbles in the sight glass (usually only found on commercial refrigeration equipment and on some residential air conditioner or heat pump systems) the charge may be low

- if the cooling coil is frosting over one of the causes is low refrigerant charge

- if the compressor makes a horrible clanking sound and then stops dead, one of the possible causes is overcharging or another problem (such as a failed TEV or other refrigerant metering control) that has caused liquid slugging of the compressor on the suction side.

Beyond these observations, you need to be able to trust your HVAC technician. While mistakes are of course possible, no service tech any credible motive for placing an improper refrigerant charge into the system. Doing so just makes more work and trouble for everyone.

Question: replaced the compressor but it's still not cooling and pressures look wrong

(Aug 16, 2012) John said:
I got a question had my compressor replace and it's still not cooling the high side line is low and the low side is way to height like of 100 and the high is around 200 what could be the problem beside the company that put it in

Question: refrigerant pressures keep jumping up and down

(Sept 5, 2012) joe said:
low side pressure jumping up and down


Joe, a sticky TEV can cause odd pressure variations but if you are just seeing the gauge needle vibrate over a small range I suspect that's just an artifact of the compressor motor itself.

Question: how do you know if you got air into the refrigeration system?

(Oct 25, 2012) Bob W. said:
How would you know if you introduced air into an R22 system when charging?Would the low side guage fluctuate or would the reading on the low side bounce up and down?I charged my heat pump and the low side guage is reading a steady 70psi with no bouncing movements on the needle. Do you think I'm ok?


Air in the refrigerant system won't cause pressure gauge needle bounce, more likely that's an artifact of vibration or compressor operation. Too much air contamination would change refrigerant operating properties and accompanying moisture might freeze up an expansion valve or cap tube. The fix for that problme is ugly: evacuate the system and reinstall the proper charge - something you dont' want to do if it's not necessary.

You're probably OK.

Daniel F

Question: Rheem 15 seer 4 ton heat pump split system refrigerant connections

(Jan 20, 2013) Spongebert11 said:
why the compressor keep in operation while removing the compound gauge in closing for the system?

(Mar 25, 2013) HomeOwnerCharlie said:
a rheem 15 seer 4 ton heat pump split system. the new condenser has 3 freon connections. the old lennox was only a normal air conditioner system and it had 2 freon connections. i am familiar with liquid and vapor lines and connections, but the 3rd connection appears to be another liquid line. can you tell me what it is. the connection has a cap and a schrader valve, but no shut off valve. can you tell me what that 3rd connection is for.



(Jan 25, 2014) humphrey said:
you keep the HVAC compressor running when disconnecting the gauges to maintain the differences in pressure

Homeowner Charlie,

Come compressor units are able to handle two or more separate refrigeration piping loops, for example supporting multiple split-system cooling units. Or perhaps what you see is provided for a line used when in heat mode.

Question: pressure readings 75 psi low 240 to 280 on the high side - yes it bounces

(June 18, 2014) Brian said:
my 2006 house 3 ton unit- little to no condensation inside- pressure readings 75 psi low 240 to 280 on the high side - yes it bounces. House cools. 74F inlet temp, 54 supply temp. 90F outside temp. should I be concerned about by metering valve that might be causing my bounce?


Brian I think it's worth looking-at. Look for dirt, contamianation, or frosting / icing.

Question: why do we use hoses with knurled connectors on refrigeration gauges

(Sept 14, 2014) rash said:
hi.what is the reason for fitting a gauge hose ends with brass knurled nuts?


Rash the knurling permits the technician to attach and detach the fittings by hand without using tools.


(Feb 6, 2015) Ben said:
i see grafts and what ever, but not a HIGH (?100-125) LOW (?25) i said the new unit sounded like it was working to hard (breathing) they said the freon was too high and let some out. i can't make heads or tails of what i've read so far in reguard to high/low



I'm a bit confused by your question too, but it's fair to gripe if you're not finding the info you need here. I'll review the article above to see what I can add about specific example HI and LO pressures. Understand that the actual reading of refrigerant pressure MUST be understood or interpreted along with a table giving the specific refrigerant as well as ambient and system temperatures.

Since the cooling system cannot manufacture its own refrigerant, if the refrigerant charge was too high according to your service tech, then the system was previously over-charged during service. Quite possibly the problem is elsewhere.

Question: we don't have a leak but gas pressure drops in just one or two days: what do we do?

(Sept 22, 2015) Dipesh Upadhyay said:
In our split Ac , we did not get any leakage but gas pressure reduce in just 1 or 2 days. What should we do?


Dipesh you cannot assume that a pressure variation measured on an AC or heat pump system necessarily means there is a leak. HVAC refrigerant pressures vary over a range depending on temperatures outdoors, indoor temperatures, thermostat settings, length of the on-cycle of the compressor, even outdoor humidity or other factors that affect the heat exchange rate of the condensing coil.

Other variables include changes in the metering of refrigerant in the air handler - e.g. if a thermostatic expansion valve is dirty or icing it may behave erratically causing varying pressures.

Further an HVAC system, most of them, include a receiver that holds a buffer quantity of liquid refrigerant at the condenser unit. Operating system pressures may vary but remain un affected by a refrigerant leak until enough refrigerant has leaked out of the system to cause a change in its operating temperatures.

Question: equpment motor on or off during re-charging

(Feb 9, 2016) Lisa said:
When regassing a freezer, do you leave the motor running or turn it off?


Usually we had the compressor running and monitored suction line temperature as well as monitoring the refrigerant charge quantity.

Question: can we test refrigerant charge without having to re-charge the system?

(Aug 1, 2016) Is it possible to test the refrigerant charge amount and then charge it later ? - Andy


Yes sort-of. To test refrigerant pressures safely the refrigerant lines and gauge should be connected to a refrigerant source so as to be sure not to accidentally push air into the system nor leak refrigerant out of it. Just how much of a risk that is depends on the age and type of systems and the design of its service port. But in sum, certainly an actual "charge" of refrigerant is not needed to check pressure.


Continue reading at REFRIGERANT PRESSURE READINGS & CHARTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.






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