The details are a little sketchy as I replaced these actuators a few months ago, but I’ll try to be thorough.

All of these actuators were replaced due to the thumping or knocking sound they were making. 3 of them came off the same truck and the 4th from another truck of the same era/generation - I don’t remember the exact years but they in the 2000-2005 range.

There are A LOT of possible causes for actuator failure - the thumping/knocking sound in particular is typically due to stripped or broken teeth on the gears. It is also possible to repair these, but I don’t know where you would source the parts if you were motivated to do so.

2 of them were for the driver/passenger temp blend doors, 1 was for the recirculation door, and 1 was for the mode door.

In the first pic, note that despite having different purposes, they are all the same part#. It’s not true for every vehicle out there, but on these trucks, the actuators are interchangeable.



The case can be opened by releasing the tabs around the perimeter.



It’s a pretty basic set up. The HVAC module provides 12V power and ground to the motor. The motor turns the gears, which rotates the door position. I didn’t take a pic of the individual gears (or do the math to figure the ratio) but the set up allows a significant mechanical advantage to the motor, making door operation relatively easy work.




I didn’t find any stripped or broken teeth on the gears, but I did notice that the drive gear on each motor appears to be “necked” or stretched. I know the doors for these actuators were moving freely (something I always check when replacing them) so I suspect the root cause of failure was the drive gears were stretched enough that they couldn’t grip the teeth of the driven gear any more and just started skipping. Unfortunately, the lubricant (some kind of Vaseline or dielectric grease) prevented any scarring of the gears if this was the case, so I don’t know for sure.



Back to the operation for a moment - the gear that attaches to the door shaft has a contact wipe on it to provide feedback to the HVAC module about actuator position. It works exactly the same as a TPS (potentiometer). The module provides a 5V reference to the sensor circuit, and as the actuator rotates and changes position, a return voltage signal tells the module what the current door position is.




And one pic of the motor disassembled. Just because.