i have a 2003 cavalier with 156k miles.. everything is pretty much stock and whenever i turn on my car and turn on the a/c the rpm goes down to almost 500 and goes back up to a little under 1000 and also the turning signals and the lights on the speedometer dims a little then goes back to normal, one last thing idk if its just mine but when i have the a/c on i get way less power than if it would be off any help on what it could be? i think i might need a new compressor

 

remove the belt and turn the compressor by hand. make sure your turning the compressor not just the compressor clutch. It should have slight to moderate resistance.


if that is ok, you may have an idle air control valve issue. when the a/c is turned on the iac opens to raise the idle to compensate for the added load on the engine. without the raised idle, the engine may stall or near stall.