1995 ac/damper control failure

I have a 95 suburban 6,5TD. I experienced som trouble with my ac/vent system. Suddenly, the damper system sort of collapse and i only get air on my feet and the ac will not turn on. I can turn the knobs as much i want, but no response. This would be ok again after stopping the engine for a while. But now it's final! the dampers will not operate and ac will not start. I am a refrigeration engineer so i know the refr. system is ok, but it all hangs together with the damper system. The fan speed controls are ok. What could this be? I have checked under the dash where the damper motor is located, when i turn the knob the motor/damper moves extremely little. This must mean that some signal arrives to the motor??? can it be the motor?? Please help anyone. It is a hot summer.....

your problem is the ac control unit go to the dealer with your vin and they will replace it for $100-120 dont go to the junk yard , they all go bad once or twice in a surburbans life time . i know it happ to me .