Chevrolet Repair: 2000 silverado heater control problem, controller module, fan control

Question
Hi,
 I have a 2000 siverado. My heater temp. selection has a problem. When I turn my heat to the hot setting, then back to cool, the temp. will not change. It will continue to blow hot air. Sometimes if I turn the fan control to the "OFF" position, and turn it back on, the temp. will change the correct cool setting. Also...while this is going on, I'll try to turn on the A.C. And this will not cool the air either.
 My guess is, there is a wireing connection problem somewhere, but I'm just not sure where this could be.  Any suggestions?   Thank you in advance. N.C.

Answer
Hi Nick,
The air is directed either through the heater core, or around it, by a little door that is operated by a stepper motor.
I have seen the motors bad, as well as the controller module in the dash.
If the motor is bad, you can usually hear a can opener like sound under the dash, but nothing happening.

Van