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.
Green links show where you are. © Copyright 2017 InspectApedia.com, All Rights Reserved.
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 motorJohn,
On 2017-04-07 05:43:58.160911 by JohnThanks 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 refrigeratorAlvis
On 2016-12-30 21:47:10.741357 by ALVIS JENKINSActually 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 JENKINSWouldn'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 surajY refrigerator both tune gets ice
On 2015-10-29 14:34:19.929772 by Ravi SharmaPlease 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.
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 - email@example.com 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.
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.
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.
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.
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.
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.
(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
(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.
(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.
(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
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.
(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.
(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.
(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.
(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.
(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.
Or see TEV INSTALL & REPAIR
Or see LOST COOLING CAPACITY
Or see these
Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING & HEAT PUMP SYSTEMS.
If your air conditioning or heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.