When you energize the A/C first of all, do you hear the compressor relay operate. The compressor relay is controlled by the engine control module, with that being said, if there are faults within the PCM(current or history) it can inhibit the operation. The all out best way to check this would be with a scan tool, you could also control the compressor relay with the scan tool that will get you further in diagnosis. If the system is low on charge, the ECM will also inhibit operation.
Same on the rear defogger, can you hear the relay click?
If it does, or does not, swap it with a similar relay in the underhood fuse block and recheck. The circuit goes through the antenna amplifier(probably because the grid acts as the radio antenna as well. The next step would be to go to that amplifier and check for power on pin 1, a black wire, with a test light to ground. If there is power there, check at the grid, also with a test light to ground. If there is power at the grid, check the continuity to ground from the grid, with an ohmmeter. Let me know the results.
Friday, May 28th, 2010 AT 12:17 AM