Thinking about what is happening, the front defroster also defaults the a/c compressor on. I did a search for service bulletins on the symptom, and it turns out there is one that may be of aid. It is relatively simple, and low cost;
#PIT3116A: Engine Stalls When Air Conditioning Is Turned On At Idle - keywords HVAC rough condition CJ2 CJ3 surge - (Dec 15, 2006)
Subject: Engine Stalls When Air Conditioning Is Turned On at Idle
Models: 2004-2007 Buick Rainier
2002-2007 Chevrolet Trailblazer and Trailblazer EXT
2002-2007 GMC Envoy, Envoy XL and Envoy XUV
2002-2004 Oldsmobile Bravada
2005-2007 Saab 97x
This PI was updated to include models through 2007. Please discard PIT3116.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Engine may stall with the air-conditioner on and or while adding additional loads to the engine at idle. An example of an addition load would be turning the steering wheel left or right with the air-conditioning on. This type of stall usually occurs during idle or slow parking lot maneuvers. This concern may not set any diagnostic trouble codes.
Clean the throttle body bore and the throttle valve plate using a clean shop towel with GM top engine cleaner, GM P/N 1052626 (Canadian P/N 993026) or AC-Delco Carburetor Tune-Up Conditioner, P/N X66-P, or an equivalent product.
Saturday, April 3rd, 2010 AT 12:17 AM