OK. Lets try this question here...

I've got a '92 SE, and I'm having trouble with the A/C / heat switch, or at least I think it'* the switch. When I go to turn on the A/C, the compressor does not engage. Also, the airflow won't change to defrost.

Is the switch bad? Could a relay be out, and if so, which one? I was also told that it might have something to do with a vacuum line.

Any thought or ideas would be extremely helpful. My son will be taking this car to college in the next month, and I don't want to sink a bunch of money into the fix if I can do it myself.

Thanks in advance!