HVAC Air Door Actuator by Dorman®. Defrost. Location: To Main Unit. Dorman-engineered with robust materials to improve durability and performance, the HVAC Heater Blend Door Actuators restore and maintain proper functioning of the HVAC Heater Blend Door. Depending on the make and model of your vehicle, the same exact actuator could be suitable for any and all climate control blend door applications.