Installed a new CD/DVD player in 1999 TA Saturday and now the A/C compressor is not getting power. I used one of those radio wiring adapters to keep from cutting the factory radio harness.
I think the theft deterant system is stopping power to the compressor, because, there is power at the a/c selector switch. The power leads from the selector switch to the ECU, but not from the ECU to a/c compressor. Once I figured this out I tried puting the the factory radio back in and it won't even turn on now! The factory radio was fine when it came out. I have heard of GM theft systems on the radios that need a code to turn radio off, but never heard about the a/c not working.

Any suggestions???

 

Is it possible you blew a fuse in the panel at the end of the dash? The A/C control system and the radio may pull power from the same fuse. Check your Owner's Manual for a list of what is powered off of each fuse. In any case, doesn't sound like a computer related problem. Sound more like the wiring or a fuse got messed up. Are you sure you didn't knock some wiring loose when you were installing the radio?

 

If it is not a fuse check the relays under the hood. The AC is beside the air pump relay, since they are the same, switch them and then see if your AC works. That happened to me then go to GM and get a new relay for your air pump.

 

The 20 amp under dash fuse also feeds the blower motor, does that work ?. The a/c switch then feeds +12 V to the PCM. The PCM picks the a/c relay in the under hood electrical panel. Per post #3 swap relay then make sure 15amp a/c fuse in under hood is good (that fuse also feeds cruise control). The radio should have nothing to do with the a/c operation. As far as radio not working, check fuses #3, 4, 7 & 17 in the interior fuse panel.

 

Since it happened when you were messing around near the control head, it's almost certainly a wiring issue caused when you were working, IMO. You can jump the A/C relay underhood to force power to the clutch - if that works, the clutch and wiring are OK. You can also check for the PCM signal at the relay pins to see if the car is trying to command a/c on. That's a great location for diagnosing compressor engagement issues, and the relay has a diagram on it to show you what pins to check.

There is another, more obscure possibility. Have you perhaps lost refrigerant? I recently tried to recharge my '95 a/c system. No power to the clutch, car would not command the relay on, either. I found there is a code for 'low refrigerant charge' that sets and locks out the clutch to keep you from frying the compressor. I cleared that, and now the clutch relay gets engaged as normal. I don't know OBD2 very well, but GM still uses that feature, so there's a good chance your car has it in one form or another. Look for a code set.