91 AC problems
Thread Starter
Heel & Toe
Joined: Mar 2015
Posts: 23
Likes: 1
From: Dubai
91 AC problems
Can anyone point me in the right direction?
I have a 91 C4, the air con was filled about two months ago and it worked great. I left the car parked for about 3 weeks and when I came back the a/c wasn't working (the compressor is not engaging). I live in Dubai and temperatures are 40+ atm so I basically can't use the car without a/c. I am from the UK where temperatures rarely reach 20 degrees therefore I have limited knowledge of a/c systems.
What I have done so far:
- The a/c fault light is not flashing and therefore no fault code is found
- there is no power reaching the compressor
- there is no power reaching the low pressure switch
- the compressor doesn't engage when I jump the low pressure switch
- the compressor will run if I put power directly to it
- the fuse is fine
- I borrowed an a/c pressure tester and the red line (high pressure) side read good pressure, i couldn't test the low pressure side as I didn't have the right adapter
What should I try next? I can't find the a/c relay I checked under the dash but couldn't see it.
thanks in advance
I have a 91 C4, the air con was filled about two months ago and it worked great. I left the car parked for about 3 weeks and when I came back the a/c wasn't working (the compressor is not engaging). I live in Dubai and temperatures are 40+ atm so I basically can't use the car without a/c. I am from the UK where temperatures rarely reach 20 degrees therefore I have limited knowledge of a/c systems.
What I have done so far:
- The a/c fault light is not flashing and therefore no fault code is found
- there is no power reaching the compressor
- there is no power reaching the low pressure switch
- the compressor doesn't engage when I jump the low pressure switch
- the compressor will run if I put power directly to it
- the fuse is fine
- I borrowed an a/c pressure tester and the red line (high pressure) side read good pressure, i couldn't test the low pressure side as I didn't have the right adapter
What should I try next? I can't find the a/c relay I checked under the dash but couldn't see it.
thanks in advance
Thread Starter
Heel & Toe
Joined: Mar 2015
Posts: 23
Likes: 1
From: Dubai
Ok so i found 3 relays under the dash I swapped the one nearest the column for the one in the middle, I now have power to the low pressure switch (I'm not sure if this is just a coincidence and maybe I just didn't have my multimeter in properly when i checked before but anyway) the compressor still doesn't engage but will engage when I jump the switch, however I still get no cold air so I'm now thinking I may have a leak in the system. I'll try and get the pressures checked properly tomorrow.
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 41
From: Baltimore, MD USA
Ok so i found 3 relays under the dash I swapped the one nearest the column for the one in the middle, I now have power to the low pressure switch (I'm not sure if this is just a coincidence and maybe I just didn't have my multimeter in properly when i checked before but anyway) the compressor still doesn't engage but will engage when I jump the switch, however I still get no cold air so I'm now thinking I may have a leak in the system. I'll try and get the pressures checked properly tomorrow.
You never mentioned the AC static pressure you measured. If the compressor is not running the hi and low side static pressure will be the same.
The low pressure cycling switch should be closed if there is at least 47 psi in the system.
You should not have to jump it. If there is over 47 psi and the switch is not closed, the switch or the wiring to it is bad.
Since you jumped the switch and there was no cooling, most likely you're low on refrigerant.
Your static pressure should measure close to what the cart shows.
At 80F or 27C the static pressure for R12= 84 psi for R134a=87psi
At 100F or 38C the static pressure for R12=117psi forR134a=124psi.
Last edited by Hooked on Vettes; Jul 3, 2015 at 09:46 AM.
Thread Starter
Heel & Toe
Joined: Mar 2015
Posts: 23
Likes: 1
From: Dubai
Thanks for the replies and info.
I think both of the schrader valves may have been leaking slightly so I replaced the valves and got the system re gassed. It is now blowing cool (but not exactly cold) air. I poured water over all the joints and valves and there didn't appear to be any bubbles so i'm hoping the problem is now fixed.
How long out of curiosity should an ac system last before it needs re gassing? If say it was being used for an hour every other day?
I think both of the schrader valves may have been leaking slightly so I replaced the valves and got the system re gassed. It is now blowing cool (but not exactly cold) air. I poured water over all the joints and valves and there didn't appear to be any bubbles so i'm hoping the problem is now fixed.
How long out of curiosity should an ac system last before it needs re gassing? If say it was being used for an hour every other day?
