Question : AC Compressor Won't Engage

[PCGUY112887]

When I first got my GP, I am fairly certain that I tested out the AC and it worked fine before I bought it. When I did my motor swap, I just tied up the compressor and all AC components and swapped the motor around then, then bolted the compressor back to the block.

Ever since then, if I try to turn my AC on it never gets cool. I figured maybe it had a leak or was low on refrigerant, so I never really worried about it since I never use AC. I was visiting my mechanic one day and asked him about it, and he tested the line and said my refrigerant pressure was just fine. We started the car and kicked it on, and he pointed out that my compressor never even engages. It doesn't seem to engage when I put on my defrost either. He thought maybe it was an electrical issue, but I didn't want to pay for him to poke around and find it.

Does anyone have any idea what could have gone wrong and why my AC compressor won't engage even though I have refrigerant pressure?

Thanks.

[55trucker]

The problem might not necessarily be the compressor itself, might be the clutch that has failed or the wiring to the clutch has an open in the circuit.

[IsaacHayes]

Pull the connector off the AC compressor. Measure voltage to it and make sure that it's even getting voltage to turn on. If it is, then well the clutch coil is fried.

Next, if no voltage to kick it on, but you are POSTIVE the AC pressure is enough to kick on, it could be a short in the wire somewhere, or possibly the low pressure switch is faulty and thinks that you don't have enough pressure to turn on.

Do the rad fans ever kick on when you turn on the AC?

[PCGUY112887]

Alright, just got to looking at this today.

I press the AC button on the dash, the light comes on, the compressor never engages, and neither cooling fan ever turns on.

Turn the switch off, the light goes off, and that's it.

[3400-95-Modified]

Whats the pressure in your AC system. If its too low the compressor will not turn on at all. Go get one of those charge cans from autozone with a gauge and put it on the L pressure side, (typically a blue cap) and see what it says. A charged A/C system in the off state will have in upwards of 100PSI on the low side, once engaged the pressure will drop to the 40-45 range for acceptable pressure, if its lower than 20 the system will never turn on.

I say double check it even though the tech said its fine. After that yes you can replace the compressor clutch magneto or the whole clutch assy...

And pushing the switch and having the light come on does not mean that your getting 12v at the plug on the compressor, you need to check that with a meter.

[jmgtp]

Mine didn't work for a whole summer. Given the cars age, I assumed that it was too low on refrigerant to kick on.

The problem turned out to be my power steering high pressure switch. I don't remember if it was unplugged or shorted, but it was one of those two. Worth a shot in the dark to check if you run out of ideas. The switch should be located on the drivers side of the rack near where the steering column joins - at least on my 91. This car still has the coldest a/c of any car I've owned.

[SofaKingWeToddDid]

i had this problem with my buick regal. someone told me its tied into a sensor on the power steering ?? i dont know if its true, the only way i could see if the clutch was engaging was to pull the relay and use a wire to make the connection from 86A and 30A *i think* the power in, and the triggered power out. i forget what the other one is, but one is 30 forsure. then with the engine running, the ac compressor would turn. but the button on the dash did nothing but light up when pushed. so i gave up on it and just used good ol natural AC and opened the windows.