Auto Air Conditioning & Heater Repair: a/c compressor clutch not getting power, powertrain control module, buick park avenue

Question
no power to engage a/c compressor clutch on a 91 buick park avenue.i back stabbed the plug on top of the compressor and put 12 volts directly to it.the cluth engages and compressor works fine. the two relays at the firewall on right side were swapped (same part number) with no results.wire schematic shows a a/c compressor relay and a powertrain control module in the loop for getting power to the clutch.where is this pcm? any input would be appreciated.

Answer
There are numerous sensors that can prevent the system for operating and they ALL need to be tested first.

Your problem is most likely to be a LOW FREON condition due to a leak in the system. You need to put a set of gages on the system and engage the compressor and read the high and low pressures to determine if you have enough freon in the system.

Without the proper amount of freon in the system, Nothing you replace will solve your problem.

The pcm is located under the dash but I doubt that this is your problem.