I have A 94 k3500 and my heater control panel shorts in and out, When it does come on its only on low and as soon as I try to put to med or high the whole screen goes out.I have changed the control panel,blower motor resister and pulled fan out and tested it all made no diffrence,I got it to go on med for a few seconds but it was not blowing any air out, when its on all the other controls work fine just when i try to turn up blower it kills the whole screen I dont know what else to do any help would be great.

 

I take a shot in the dark and say your BCM is sending incorrect signals. You have electronic door actuators BUT they dont affect air flow only distribution. And you have replaced every else.

 

Whats the BCM and where is it?