What Pressure does A/C Compressor Come on?

Nagash01WS6 · Sep 13, 2004

Im trying to identify the source of my A/C leak right now... so I dumped a can of 134a in and the compressor would come on at ~105 psi and compress it down to ~85 or 90 and shut off. I assume I still dont have enough 134a in there for it to run correctly... but at what pressure should it be at to run correctly???

DJHA90 · Sep 13, 2004

Are you testing on the Hi side? Low side pressure (where you add the r13) should be between 25-45 lbs.

Sleepy McNastee · Sep 14, 2004

Pressure is directly related to temperature. What probably happened is your system coooled after you left it on and therefore your presuure dropped. This could also mean that you do have a leak, if the pressure keeps dropping.

For example, a high side pressure of 120psi means a high side temperature of about 120 degrees farenheit. Hope this helps.

Sleepy McNastee · Sep 14, 2004

Your pressure seems low though. Normal operation @85 degrees (ambient temp) for R-134 should be:

Low side: ~30-31 psi
High side:~200-210 psi

You are almost certainly low on refrigerant. I would get some R-134 leak detector. That way you can see where the leak is.

As for your original question, it depends. If your system doesn't have the proper amount of refrigerant, your thermostat or pressure switches might not work right.(I can't remember if our systems run off pressure switches or a thermostat.) Either way, without the correct pressure you will probably have clutch cycling problems.

Nagash01WS6 · Sep 14, 2004

Hrm... I thought I was on the low pressure side... drivers side... right underneath the strut tower brace... little fitting there.

Im pretty sure it was completely out... because this is the first time ive ever seen the compressor move.

maypo59 · Sep 14, 2004

IF it was completely out, it will take more than one can to bring it up to the proper amount of R134a. If you are seeing 85-90 psi on the LOW preasure side, which is the side under the brace on drivers side, there is something else wrong with your system. You might try jumping the switch on the accumalator to make the compressor cycle, then check your low side preasure. You should use a leak detector also, to pinpoint the leak, although in my exp. if it has a big enough leak to empty the system, it should a leave a large oily nasty residue where the leak is.

Sleepy McNastee · Sep 14, 2004

Yeah, if you have ~90 psi on the low-side thats a BIG problem. But I am almost sure you were checking the high-side. Anyway, ~90 psi on either side is not right. You need more refrigerant in there. Without knowing how much is actually in there, I can't say how much more you need.

Also, make sure you put in some oil(PAG) if it is not included in the can of R-134. Your compressor needs lubrication.

worksneaker · Sep 17, 2004

I have a realted problem

1999 Cobra wit the A/C working fine until it just quit. I figured the R134a was low since it was never recharged but when I put the meters on it to refill the low side (yes Im sure I was on the low side by the fire wall) read 100 psi) Whats up with that? I verifed that the compressor clutch is not activiated so some safety thing is on but whats causing the high pressure??

mo_dingo · Sep 17, 2004

The low side is the one on the driver's side of the car. You need to loosen the STB to get access to it.

If you are seeing 90 PSI in that side, something is wrong. My GUESS is that air is in the system (from the hole), and it's trying to compress the air, which is really bad. That my only guess why you are seeing that much pressure on the low side.

You need to find the leak first. Get some flourescent dye, and add it to the system. How? I honestly don't know. Do some research on the web.

It will take more then 1 can, if empty before, to get the system to cycle on/off.

If you are filling the freon on the high side, stop right now. I hope you didn't break anything.

All systems imploy a pressure switch. This prevents the compressor from coming on when there is no refridgerant present. Do not bypass this switch unless you are 100% sure the system has the correct amount of refridgerant. The compressor will blow, without a doubt.
Scott

What Pressure does A/C Compressor Come on?

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