e36 A/C charge pressure minimum pressure for compressor to turn on

[scooper]

Hi, I am trying to diagnose why my a/c is not working anymore. Took a long trip up 95 for around 9 hours each way. The a/c stopped blowing cold halfway on the way back. Got home. Replaced no.39 fuse (7.5amp brown one) but still no cold air. Low side reads 92 psi. High side 100 psi at roughly 78F. I charged it properly and it was working for a year or so. It actually blew really cold and was great. Aux fan works. Idle drops when I switch on a/c.

What is the lowest pressure that the system will turn on the compressor? I read that if there is not enough pressure the compressor won't be turned on. I think 92/100 without the a/c on should be enough pressure for it to come on? Especially since it had been working...Thanks for any insights.

[AJLM34A]

Fuse 39 only controls the compressor relay. You need to disconnect the compressor's power wire and see what the magnetic coil reading is with an ohm meter. I think it is around 3 ohms but search on here, it might be posted. You can also check the coil is working by using a fused jumper wire from the B+ post to the single compressor lead.
726887

[scooper]

Thanks for your advice! Disconnect that power plug from the compressor and read the resistance when a/c is turned on? I will ground the black lead from the multimeter to the metal of the car chassis....

Any other ideas? Thanks in advance!

[RRSperry]

92 low> It's broken Edgar. a 134A system low side should be 35-45 and high side should be 150 to 170 ish at 75F (depending on ambient) You probably have a pretty good leak, or the compressor is shot or the expansion valve is shot. What you really need to do is evacuate the system of the 134A and pull a vacuum on it. You could also add the UV dye and try that. The easiest thing is let a shop do it. They know how and have all the correct equipment.

[ryza]

Typically, the compressor needs a minimum low side pressure to kick in, usually around 20-30 psi. So, 92 psi should definitely be enough for the compressor to engage. Since your aux fan is running and the idle drops when you turn on the A/C, it’s not that simple.


It sounds like you might have a refrigerant issue. You could be low on refrigerant or have a leak somewhere. Also, check if there’s a blockage or issue with the expansion valve. If the pressures look off or you’re still not getting cold air, it might be time to get a pro to check the system more thoroughly.

[scooper]

Finally jacked up the vehicle. Original A/C compressor is shot. Ordered new belts and pulleys. Thanks guys for input.