GM Genuine Parts HVAC Heater Blend Door Actuators are designed, engineered, and tested to rigorous standards, and are backed by General Motors. These actuators are electric motors that receive a signal or command from the HVAC controller and either open or close the heater blend door. The blend door's open or closed position determines the temperature of the airflow traveling through the HVAC vents. GM Genuine Parts are the true OE parts installed during the production of or validated by General Motors for GM vehicles. Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE).