Ok i just had my entire ac system replaced by a shop minus the evaporator and even charged with r12. This was in july last year. This morning it was about 34 and my windshield was iced up so i started ut up and ran the defroster. I went back out and the ice was gone but it was fogged up. I noticed the ac clutch wasn't engaging no matter what setting. By the time i got to work (20 min later) it cycled but it did come on. My question is does it have to be a certain temperature for the ac clutch to engage or is something else going on?