My A/C never worked since I bought a car. I really need to fix it now. Problem is: compressor clutch do not engages, because AC relay is not getting ground signal from PCM. If I jump relay with wire - clutch activates and AC is working, blowing cold, and sounds ok. I know that pressure switch tells PCM to disable AC when coolant pressure is too low. I checked it and it seems way too high - almost 95psi on low-pressure end. Is there another threshold in PCM for high pressure? May be I need to let some R134 out and then reset PCM? My PCM was recently reprogrammed, may be problem is in it... I appreciate any help. Thank you.

 

My bad, I checked pressure when compressor were not running. After checking on running compressor (jumping relay) I got 10 PSI. Too low. I charged it to 40, tried resetting PCM, jumping red pressure switch wire to gray - no luck, still not working. It only works when I jumped AC relay. Still no ground signal on relay... Please somebody, throw me an idea. I know nothing about AC system...

 

I'm having the same problem. My car's ac worked before I did a v-6 to v-8 conversion. I got a new pcm along with getting it reporgrammed, sence it went to a obd1 to obd2 computer I had some wires that were not connected. The next thing that I'm going to check is to see if the wires are running to the sensors, and the clutch start. I know shoebox has the schematics for it.

 

Can it be A/C evap. temperature sensor? To narrow things down to pcm what signal should I put on pressure sensor (I assume short red to gray wire) and evap. temp sensor (probably 5 volt too)?

Yes Found it:
http://web.camaross.com/forums/showt...hreadid=257680

I'll check everything tommorow.

 

Checked everything today. Signal "AC On" from AC switch, evap sensor, R134 pressure sensor, contact between PCM and relay, +5v on all sensors, all contacts - everything good. Simulated sensors, etc... Evens fans are coming when AC clutch should be engaged. It's PCM AC clutch relay curcuit. Some damn transistor there is burnt. I guess someone tryed to jump AC clutch with wrong pins on relay on this PCM, need to exchange it