I have a 2004 Trailblazer and when I turn the a/c on the engine idle drops and dies while in gear,

donaldgriner

I have a 2004 Trailblazer and when I turn on the a/c the idle drops and dies, only does this in gear and stopped.

Mr_Shiftright

The primary suspect would be a dirty throttle body/throttle plate, but that's just a guess. Also the idle air control valve could be a culprit (IAC valve).

CDerrickBailoey

I had this problem as well. Noticed that with AC on, idle speed would drop to 600 rpm and had no power going uphill. Opened up the air intake, cleaned filter, and cleaned back of throttle body plate as well as where it seats when closed. Fixed the problem.