The feedback potentiometer is a variable resistance device used on older automatic temperature control systems where the in car temperature could be set and the system would maintain that temperature using both air conditioned and heated air. The feedback potentiometer is used to monitor a specific position of doors in the plenum.

On automatic temperature control systems, the feedback potentiometer would monitor the position of the blend door. The blend door is used to mix the air entering the vehicle so that you get the best temperature control. Understand that on air conditioned vehicles, when the system if functioning properly, there is always air conditioned and heated air available. The flow of water to the heater does not shut off. Therefore, the blend door can direct a mix of hot and cold air into the vehicle to maintain specific temperatures and provide better passenger comfort.

The feedback potentiometer is used to monitor the position of the blend door and report that position back to the control head on the dash. Depending on temperature settings, the control head works to alter the position of the blend door to maintain specified in car temperatures.