92 Camaro RS. AC had been working fine....then the blower motor went out....replaced that....AC worked fine. Then...out of no where, my AC controls started acting funny....first, anytime I turned it to the off position....I could hear a pretty loud sound that sounded like a hissing sound...but if I just slightly moved the control ****...it would go away. And then recently....the controls stopped working all together....I can move the **** in to any position (AC, heater, defroster) and nothing works...the compressor doesnt kick on.....the fan doesnt blow, but i still hear a hissing sound. One day, it was iced over here...and cold as hell...so I kept moving the controls back and forth...and after about five minutes...the AC kicked on.....I moved it to defrost..and it didnt work...and from then on it hasnt ever worked again. What could the problem be? I know nothing about the AC system. Oh one last thing i forgot to mention....before the system went out on me...the compressor was acting funny. First, I noticed that anytime the AC was on..and the compressor would kick on...my RPMs would drop WAY down...like my car was about to stall....and then it would turn off and my rpms would go way back up...and it would do this anytime the AC system was on about every 10 seconds....I dont think this is normal....and like i said....the compressor would engage every 10 seconds.....no matter how long it had been on...I thought it was supposed only do this for a little bit.

 

Your HVAC control unit may be dead and or the vaccuum line that switches between all that stuff may be leaking. I would check for the vaccuum leak first, just pull it out and check everything out. I haven't done one before but I have had it apart and it is cake. I have only heard about this once and the guys problem was the plastic hose had cracked going into the HVAC control.