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A/c gauge readings in 90 degree heat

Im charging my a/c in my 2002 echo. it's 90 degrees outside so what should my low and high pressure readings be on my gauges? thanks.

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Your low side should be at 30 and high side at 225.

Posted on Jul 25, 2009

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On my 1996 ss impala what low side pressure should I see on the a/c with the system running

It all depends on the outside (ambient) air temperature. Your A/C low pressure switch is designed to turn the compressor off at 24 Psi. and turn it back on at 45 Psi. Most systems will normally run at between 25 and 40 Psi when the system is running on HIGH blower and "MAX" or "RECIRCULATE". A system that is fully charged may run at 25 Psi when the ambient temperature is 75 Deg. (F) and may run at 40 Psi when the ambient temperature is at 90 Deg. (F). (it can be even higher if ambient temperatures are higher than 90 Degrees.)

To properly diagnose a malfunctioning A/C system, the HIGH side pressure must also be checked. Restrictions in the system can make the low side pressure look normal while the high side pressure is high enough to blow hoses apart. (400+ Psi.)

Sep 04, 2011 | 1996 Chevrolet Impala SS

2 Answers

I have the correct Manifold Gauges for checking the low and high side of the heat pump. How do I read the gauges to ensure that my system has the right charge? Outside ambient temperature is 85.4.

In order to know if you have the correct charge you must measure the subcooling since it is a txv unit. The outside unit will have the proper subooling you need printed on the data plate. Hook up you gauges and let thebunit run for 10 minutes, after 10 minutes check the high side pressure, that high side pressure will correspond to a saturation temp, write that number down then measure the temp of the liquid line and subtract the saturation temp from the liquid line temp, it should be the same as printed on tjhe data plate if it is higher than that add refrigerant untill you get whtas printed on tne data plate. Is there is no data plate use 12 degrees of subcooling.

May 27, 2011 | Heating & Cooling

1 Answer

I am working on a M # GPG13420901AB. This is a 3.5 ton package unit that replaced a 3 ton package unit on 1700sq/ft single level home. Old unit was working fine but was replaced when the home was...

It sounds like you are low on charge. I think you have a thermostatic expansion valve and you need to check the subcooling, you should have 12 to 15 degrees at 95. At 95 degrees your head should be about 280# for a 12 or 13 SEER unit or higher depending on the effeciency. At 78 to 80 degrees indoor depending on the humidity, that is normal. The valve will open to try to fully feed your indoor coil and it sounds like your head pressure is to low to force enough refrigerant thru the coil.

Aug 16, 2010 | Goodman Heating & Cooling

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Hi, sounds as though for this to be its 2nd compressor for such a newer unit, the superheat was not right when the compressor was installed. I don't know what freon you are using the new R-410A or the regular R-22. There's a big difference in pressure, but now I see your pressure reading and its R-22 for these readings.For a 2 ton unit, you would use the superheat charging method for a unit that doesn't use a thermostatic expansion valve ( T X V ) and not the sub-cooling. A 23 degree super heat at that outdoor ambient temperature is way to high for that unit, you will loose the compressor again!!. Super heat killed the compressor is the saying and that's a fact. Suction pressure should pull down just as quick as the head pressure unless the valves are going and weak, or you have a scroll compressor that has a valve plate that is going, or you are low on charge. With a ambient of 95*, you should be at around 270p.s.i. on your head pressure as 210 to 200 is way low. Suction line temp should be around 68 to 70, with a suction line temperature of 50 to 51 degrees, which would give you a 10 to 12 degree F super heat. I don't know when the second compressor was installed, but it has to be low on charge to be such a low head, and high super heat and you will loose this compressor again, its only a matter of time before you have a burnout. It was either under charged when installed, or has a very small leak at one of the joints. I hope the liquid line drier was replaced also. It shows me you have some knowledge on a/c operation, so you need to get that superheat down to between 8 and 10 degrees for this unit to cool properly, and leak check it also. Did you buy a extended compressor warranty? Lets get the head pressure up and superheat down and you should be OK unless the valves or valve plate is weak. Once you loose the valves, you will have a lower than normal head pressure and a high suction pressure. Compressor just won't pull down anymore. I hope I have been of help to you and ask of you to be kind when rating me. I will be here for you if and when you need me for anything.
A/C & Heating Contractor

Jul 02, 2010 | Weather King 10AJA6001AH Air Conditioner

1 Answer

A/c recharge what is thew psi for refrigerant

Below are normal car AC pressure readings with 134A.

Normal readings on high and low side with AC OFF (static pressure) – Depends on outside temperature, but normally is between 80-105 PSI

Normal low side reading with AC on high speed and MAX & engine at 800-1000 RPM’s – Ranges from 25-35 PSI

Normal high side reading ranges from 200-350 PSI
Don’t assume that if adding little Freon is good that adding a lot is better! Overcharging just a little can decrease the performance of the system and possibly damage the compressor.

With the AC on the coldest setting, use a thermometer in a middle vent. Normal vent temperature readings will vary depending on the (ambient) outside temp. The vent temperature should range from around 42-55 degrees in my experience.

If normal gauge readings are obtained and the vent air is cold – STOP don’t overcharge the system. The only proper way to remove refrigerant is with a AC recovery machine so if this is being done at home I can’t emphasize enough not to over charge the system.

Thank you for using fixya and be safe.

Jun 17, 2010 | 2002 Ford Expedition

1 Answer

I have a 3 ton Rheem heat pump that calls for about 225# pressure on the high side at about 40 degrees outside with tstat set at 70 degrees indoor.... I am confused as to why both sides of the manifold...

Where are you connecting the gauges? It sounds like you have both gages on the high pressure side. You can't hook the suction gauge to the Big line on a heatpump because that is high pressure in the heating mode. There should be another tap that says low side or low pressure, that's where you hook the suction gauge. As for adding more refrigerant, I wouldn't do that until I measure the subcooling.
If you charge it in heating unless you weigh it in you want about 10° to 15° subcooling. Then this summer you need to check the subcooling at about 95° outdoor ambient then charge it to about 10° to 15° subcooling in the cooling mode and that should be the correct charge.

Feb 15, 2010 | Heating & Cooling

1 Answer

I am working on a GE Weathertron Heat pump (Mod# BWB924A100C1; Ser# 264082948). The complaint is it is not heating as well as it once was(running a long time to heat up house). I checked the pressure, the...

It is very hard to charge a heat pump in the heating mode. The pressures are low. It also depends on the outside ambient temp. If you can turn to cooling if inside temp is above 70 degrees. Take a piece of plastic and block condensor till you get your head pressure to about 235. Not discharge temp but liquid pressure near service valve. You do not have a TXV inside I believe. Get your suction pressure up a little more It is not to low on gas. If you have temp meter attatch a lead to suction line. Temo\p should be about 10 to 14 degrees difference Between suction temp and Temp on your suction gauge. If you need a charging chart I can fax you one. Rus

Dec 04, 2009 | Heating & Cooling

2 Answers

Indoor unit temperature between 60F & 70F after R22 charge..

The pressure changes with temperature, it is not a true gauge to ensure a proper charge.

You should have a 15 to 20 degree temp drop across the evap coil. (return air vs supply air)

Can you verify that the compressor is running?
Not the condenser, but the compressor located inside the condenser (outdoor unit)

it really sounds like it is still undercharged.
Check the temp drop, let me know what it is.
Also tell me what the outdoor ambient temp is.

( for example.... 98 degree outdoors with 85 degree indoor temp could result in pressures something like 325 on the high side and 75 or 80 on the low side.
With the exact same unit, but 80 degree outdoor temp combined with 70 degree indoor temp, your pressures could read 215 low side and 55 low side. Not to mention that more efficient units often have higher pressures on the low side because they have more coil space and remove heat more efficiently)

Aug 21, 2009 | Sanyo Split System Air Conditioner

1 Answer

94 civic a/c

Look at the LOW pressure gauge reading when the engine is OFF.

On an 80 degree day, the LOW gauge should read about 56 psi or higher if the A/C system contains an adequate charge of refrigerant.
On a 90 degree day, the LOW side reading should be about 70 psi or higher.
If the LOW gauge reading is less than this, the A/C system probably needs some additional refrigerant.

Thanks for using FixYa - a FixYa rating is appreciated for answering your FREE question.

Jun 22, 2009 | 2003 Honda Civic

1 Answer

Jetta 2003 TDI

My mechanic in our town did a quick computer check. Car computer indicated a low level of antifreeze, he topped it up, cleared all messages off the car computer and said to watch the the heat guage for any further irregularities. I'll keep an eye on it, love the car, great mileage fun to drive.

Nov 05, 2008 | 2002 Volkswagen Jetta TDI

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