[chiphead]

The air door motors have plastic gears and a potentiometer to indicate position to the controller head. Once the pot wears out/gets dirty, the motor drives into the stop and strips the gears. Sometimes it will go back to "cold" if the control head is set to cold and the truck is key cycled with the door open. After awhile it will fail back to "hot". You'll also hear some clicking/thumping noises under the dash as the motor malfunctions.

For awhile there in the summer, I'd be driving and the driver's side would go to HOT. I'd stop at a stop sign, turn the truck OFF, open the door, close the door and restart truck. The AC would blow cold again for some period of time.

The fix is to replace the blend air door motor. There are diagnostic procedures on line to confirm the motors work.