First post here, just wanted to share my experience with this same issue on my wife's 2004 Tahoe. The part you need is called an air actuator. I got one off amazon for $96 and it is very easy to change. (30 mins max). See this link for instructions ---->
http://www.sparkys-answers.com/2009/...s-hot-air.html
Here is a pic of the part and the AC Delco part number.
