3800 Swap AC Compressor Output From PCM Won't Engage (Page 1/2) Goldmember MAR 31, 08:45 AM Hi, i'm looking for some help with the AC on my 3800 conversion. I have a 2003 GTP motor and PCM installed and have everything wired correctly as far as I can tell. Using Torque Pro, I can see that the PCM is reading 80psi on the ac pressure sensor. The issue I have is that the PC is not providing the ground to engage the compressor relay. Beyond the AC request and correct pressure signals to the PCM is there anything else it requires to engage the compressor? olejoedad MAR 31, 10:46 AM Are you using the three wire AC pressure switch in the high side manifold? Did you bypass the cycle switch on the dessicator? Goldmember MAR 31, 11:41 AM This is the way I have it set up: C203 D to AC relay coil Lt Blue and PCM Clear 22 AC Request C203 N to AC relay Blk Wht AC relay Dk Grn to AC compressor clutch PCM Clear 39 AC Compressor Clutch Rly to AC relay coil AC Pressure Sensor Power to PCM Clear 34 AC Pressure Sensor Signal to PCM Clear 27 AC Pressure Sensor Ground to PCM Clear 35 When I turn on the AC the engine cooling fan kicks in and the engine idle speed adjusts, so it seems that the PCM is seeing the AC request signal. I have 12v at the ac clutch relay coil and power terminal. If I jump the power to clutch terminals on the relay the clutch engages. I'm seeing 80psi from the pressure sensor in the PCM according to the Torque scanner. The PCM output Clear 39 is not closing to provide a ground for the relay coil. Could there be another input the PCM is looking for to allow the compressor output to turn on? olejoedad MAR 31, 02:06 PM Did you bypass the cycle switch on the dessicator? Goldmember MAR 31, 10:01 PM I have not bypassed the cycle switch. I will give that a shot tomorrow and recheck all of the other wiring. Thanks, olejoedad MAR 31, 11:44 PM Your other wiring is correct, per my diagrams. The light green and blue wires at the dessicator connector need to be tied together to eliminate the cycle switch on the OEM Fiero harness. It should work fine after that change is made. Goldmember APR 01, 08:46 PM I bypassed the cycle switch and still have the same result(there is enough pressure in the system to cause that switch to be closed). I checked all of the wires again and everything looks correct. For some reason I’m not getting the pcm output ground to activate the compressor relay. Not sure where to go from here. Maybe try another PCM? olejoedad APR 01, 09:31 PM What is the service number on the PCM? Has the PCM been reprogrammed? Is the pressure port on the A/C lines on the high side? I will send you a copy of my wiring diagram if you PM your email address to me. As a note, the cycle switch on the dessicator is always bypassed when the A/C system is under PCM control. Goldmember APR 02, 07:59 AM The service number on the PCM is 12209624 YCZS. I had it reprogrammed to remove VATS, the rear O2 sensor and EGR, I'll contact the person that programmed it to see if he has any thoughts. The pressure sensor is attached to a T fitting on the high pressure line and the pressure reading in the PCM matches my gauges. Thanks for all of your help so far! olejoedad APR 02, 12:28 PM Who did the PCM reprogramming?