I've been battling this one for a while now. Turns out, the mixing door actuator motor was not reacting to the knob on the control module. So, all I was gettiing was cold air, everywhere. That's a drag when you're trying to dry out the wind shield on a cool, humid Minnesota morning trying to get to work. Found a '99 in a local yard, swapped the control mod first, no luck. Then, tried the swapper with a door motor, and left the thing on the floor so I could watch. Thought I had it nailed when I watched the motor cycle one direction, then go to the other limit when I moved the knob. Then.......nothing! Now comes the part where I open the ol' wallet and cough up for a new control and motor. They say De Ja Vu can be a fun thing........but not when I saw my new parts behave THE EXACT SAME WAY! I talked to a GM Master Mechanic who recommended getting a scan tool diagnostic with a TECH II scanner. Any one seen this before?