Squealing Belt on '94 SL1

ok, so i took my car in to fix a squealing belt (sounds similar to a banshee being tortured). it's usually when i turn my car on and put it into drive that it squeals. sometimes if i have the steering wheel turned all the way to one side it'll squeal too. also when i turn on my a/c that seems to trigger it more and when it's humid or raining. the mechanic looked at the belt and tensioner, and he said both were working just fine. he proposed it may be a problem with the clutch in the a/c compressor. spraying the belt dressing only solves the problem for a couple days and i'd like to resolve the issue for longer if possible without spending a whole lot. i've read some posts from other saturn owners with a similar problem but none of them mentioned the a/c triggering the squeal so i wasn't sure if it was something else. thanks for your help...