1997 GMC Savana 2500. AC doesn't run.Bypassed relay in under hood junction box and compressor runs and cools.Pulled control on dash. Green wire on back powers up with 12 volts on demand initiated from the knob.Schematic shows that wire heads directly to high pressure control on back of compressor.Do not have 12 volts at this hp control. Ohm reading through the solid green wire back to dash shows "open".As a test brought "hot" directly from battery to the green/white wire, leaving the hp control on it's way to the PCM, but the relay did not pull in.If a wire trace is necessary, where, EXACTLY, does the green wire exit the cabin, and enter the engine compartment. Shouldn't the relay have pulled in, with the key in the "run" position, during my test of the "green/white" wire leaving the hp control?Used the battery neg. terminal as the ground for my meter.
Country: United StatesMake: GMCModel: savana 2500
Hello and thank you for using Justanswer. My name is XXXXX XXXXX X will do my best to help you with your GMC problem.The light green wire leaves the cab at passthrough connector P100. After going to the pressure switch, the circuit feeds an a/c request input to the VCM. The engine must be running for the VCM to turn on the a/c compressor clutch, you cannot just have the key turned to Run. It may be easier to run a new wire from the control head to the high pressure switch instead of trying to locate the break in the existing wire.
Diagram shows the p100 you refered to and also c100.
Is c100 the cabin side of the connector?
Will this connector be easily identifiable in passenger compartment?
Also best way to access in engine compartment.
Also, does it seem unusual for a wire that is in a sheilded bundle in an application that sees little hard use (one owner and 120k on od.) to just go dead?
It is not typical for a wire to go bad. If there is an open in a circuit it is normally because the wire has been cut or chafed. Sometimes rodents will crawl up into engine compartments and chew up the wiring, so this is something to look for. Connector C100 is the cabin side of the connector. Pull sheathing off of wire bundle and see if you can identify the light green wire. There may be more than one.
ASE Master Certification. GM World Class Certification
The info you've provided will be a big help in the next phase.
You are welcome. Let me know if I can be of additional assistance. I will continue to provide follow up even after you have accepted the answer. Use the link provided in the email to come back to this question.
In tracing the loss of power for my AC circuit between the dash control and the HP contol on the back of compressor, I now have power at the hp control. There is also now an ohm reading back to the dash control on the green wire.
I've taken apart the harness at the leg from the HP contol back to the main harness, and though I've not made a permanent repair as yet, I tested the remainder of the circuit.
Though there is now 12volt on the green/white wire leaving the HP control heading for the PCM, there is not a circuit to pull in the AC relayin the relay/fuse box.
Pulled the relay, tested it externally.
Actually by-passed the "load circuit" and ran the compressor, even topped off the charge.
Two things. If you can help.
I do not have a scan tool that reads an "AC request" to the PCM.
On the four main plugs to the PCM, where is the exact location of the green/white wire coming from the HP control?
Also, doesn't it seem possible that a problem upstream in the wiring could have caused a "driver" in the PCM, on the AC circuit, to fail?
The PCM drivers are pretty well protected against short circuits, so I do not believe the problem is in the PCM itself. The Dark Green/White from the high pressure switch goes into the PCM at connector C3, pin 25. When the PCM receives this input, it should send out a ground on the DarkGreen/White at connector C2, pin 9. See diagram and connector end views below.Connector C2 Red
Attachments are only available to registered users.
Absolute Gold. Thanks!!
You are welcome. Let me know if you need anything else.