How does this work? Not gas side, cos its fully pressurized. The compressor wont kick in. 2004 Express 2500. Turn interior control **** to a/c or max a/c. I believe all controls off this **** are vacuum controlled? What then tells the compressor to kick in? I did change the pressure switch on a/c unit. $20-00 Still no compressor. Is lead coming into pressure switch the on/off control? It seems like an electrical fault, or clutch?, so need advice where to look. Did swop fuse and relay in fuse box too.

 

do you hear the compressor relay click on?

 

Nope. Trying to figure out sequence of operation.

 

Turning the selector **** to defrost or one of the three ac settings tells the compressor clutch to engage. All the doors and so or are no longer vacuum operated. They have electric servo motors to my understanding. If you don't hear the compressor clutch engage perhaps you can run a power wire to it to see if you can get it to cycle....
here is a link to have a look at.
https://www.gmupfitter.com/files/med...llSizeVans.pdf

 

the pcm grd's the ac relay to cycle the ac compressor clutch on and off.


the pcm must see signals from the high and low pressure circuits before grding the relay. both switches must be closed for the system to operate. ac fuse 32 ign e fuse 22 and hvac fuse 10 must all work. grd the control side of the relay and see what happens. 2 pins at the relay should have powerwith key on, one should show grd and the pcm control side should be open until the pcm grds the circuit.