I had the same problem with my 2002 Grand Prix GT. After reading many posts saying it could be the blend door control or low charge I looked under the driver side dash and located the blend door control near the center, a little hard to see, about the size of a pack of playing cards. i had someone move the driver side temp control and I could see the center of the control turn which indicated the controller was wooking. I then took the car to a shop where the pulled a vacuum on the system and checked for leaks. none were found. they charged the sysytem and it has been blowing 35 degrees for the last three weeks.
Good luck,
KAKMACK
