Review on Air Door Actuator - Replaces OEM 89018365, 604-106, 52402588 - Compatible with Chevrolet, Chevy, GMC 1994-2012 - Silverado 1500 and 2500, Tahoe, Sierra - HVAC Blend Control Actuator - Heater Blend Door by Joe Meyer

The OEM actuator uses a potentiometer to adjust position. Over time, the contacts wear out and the device is constantly "chasing” endpoints. Dorman solved the problem by using a photocell to determine the position of the actuator. Seems like a great idea, but unfortunately they designed it so that the photocell doesn't sit on the final driven gear, but on the gear that drives the final driven gear. This creates a problem because there is no guarantee as to what position the actuator is actually installed in. If you don't go into detail, it took me a lot of trouble. Because of this, both of my actuators refused to calibrate. I ended up getting an OEM replacement and they worked great.