If you don't have a subscription to OnStar then just disconnect it. It's behind the passenger side of the rear seat back. My OnStar was "waking up" overnight and draining my battery almost once a week. I have not had a dead battery since I disconnected the OnStar.

You will not be able to move the IAC by pressing it. When I replaced mine there were instructions in the box for setting how far the pintle goes in. It is adjusted by screwing it in or out and should be checked with a metric ruler.

I think the compressor will NOT come on below 50 degrees but hitting the vent button is the sure way to keep it off. BTW I own a 2001 Limited so I know of what I speak.