Truck Repair: chevy heater control, chevy k2500, dash vents

Question
Van
   I have a 1988 chevy k2500 pickup w/air, 350 v8. It has the electronic type heater control,(buttons only,) It sometimes doesn't change from floor to vent or floor to defrost, will stay at the dash vents. The display shows it changing but the change is not actually made . There are no cables or anything, I think it is done with vacuum. ?                  Thanks        Jim

Answer
Hello Jim,
Actually, the changes are made with little electric motors.
The one that makes that change is right beside the gas pedal, on the end of the heater housing.
That one controls three doors, and has a couple links on the outside of the box that you should be able to see moving as you switch selections.
It is possible for the doors to get stuck, but look and see if that motor is moving anything.
Van