A/C Electrical problem

[R_Ryne]

I am having problems with the electrical system in my Grand Prix. At first the shop I took it to told me the compressor was bad and so was the pcm because it was not sending a signal out. The code they pulled was a P1546, A/C clutch status circuit low code. I declined services to do it myself. I purchased a used PCM and had it coded to my VIN number. I found out the A/C compressor is fine after testing it. My problem is that the A/C will not kick on. When I bypass the A/C relay the compressor kicks on and I get cold air from the vents. Also when piggy packing the pressure tranducer with a multimeter I get about 2 volts, so that is in range. But the compressor still does not kick in. Any suggestions?

[BNaylor]

Welcome to AF.

What year is your GP?

The PCM sends a low signal to the A/C Clutch relay to energize it. 12 volts is on the other side of the relay coil contacts either when ignition is ON or at all times. Have you checked the A/C Clutch relay to see if it is even energizing properly. Also, there is a fuse and diode in that circuit.

[R_Ryne]

My car is a 2001. Yes, I have power on the relay. The only thing missing is the PCM signal. The fuse is fine and if I am reading my wiring schematic right, the diode is after the relay?

[BNaylor]

I am assuming by bypassing the A/C Clutch relay you jumped pins 87 to 30 at the relay contacts to get the clutch to activate?

The clutch diode is after the relay at pin 87 and connected in parallel to the Compressor Clutch Coil so if you jumped contacts 30 and 87 then you can rule it out.

The PCM supplies solely a ground/low signal so you can apply a ground to pin 86 which is one side of the relay coil just to double check the relay is energizing. Pin 85 on the other side of the relay coil has the 12 volts.

According to the GM wiring diagram the PCM needs A/C Clutch Request input from the climate control unit so check that too. Also, the PCM may not send the ground/low if the refrigerant charge is either too high or low. You can ohm out the signal line from the PCM at C2 pin 39 to the clutch relay pin 86 to make sure the wiring is good or there is continuity.