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2001 Pontiac Sunfire AC problem

The compressor don’t engage when I turn on the AC. The light comes on but the compressor don’t turn on. I took it to my mechanic and they replaced the compressor and accumulator and recharged the sytem but still have the same problem. They checked all the wirings, fuses, relays and they say that everything works when they short the compressor. Now they are telling me to replace the car’s computer system. Please help.

Get a better mechanic. There is no reason to guess at or throw parts at this problem. He should have checked for power at the AC clutch before replacing anything. I see no excuse for it.

Get away from this “mechanic” and find a shop that specializes in automotive AC service. You probably already bought a compressor you didn’t need. Quit wasting money throwing parts at it. Go to an expert.

I would like to do some troubleshooting of my own before taking it to another shop. Can anyone please give me a few tips on what to check and how to check it? Thanks.


I checked the voltage output on the wire connecting to the Pressure switch and I only get 0.04 volts out of the grey wire and none from the other 2 wires. Does anyone know what it’s supposed to be?

You may need to take the car to someone that specializes in diagnosing automotive electrical systems.

My problem is I’m in Germany right now and there’s really no shop specializing in Pontiacs. I took it to the Opel Dealer once since they are GM but the car had more things wrong with it each time i took it there so I stopped going there.

Can someone tell me what the 3 wires that leads to the pressure sensor do?
Which one provide 12V power to the sensor and can I try to provide power to it from the + terminal of the battery?

My thought is what your trying to test is not a pressure switch but possibly a pressure transducer. Looking at a typical GM wiring diagram of that vintage but (not a Pontiac Sunfire specific diagram) Gray wire is +5 volt, Black wire is ground wire, and the Red/Black wire is sensor output signal wire to the PCM. Jumping out any wires, and or applying straight battery voltage to this circuit may fry the powertrain control module, and or the pressure transducer.

Only getting .04 volts on the gray wire could be a indication that The powertrain control module if defective.

Thank you for giving the very first advice that actually provided some helpful information. But I would like to continue the process of elimination before considering a faulty PCM. Would it be possible then to provide +5V to the grey wire to check the state of the transducer? I’ve heard it called both a switch or a transducer btw…=)