Just as a side note, when there is a lot of traffic, posts get lost quickly, I did not see this and it is a subject I am interested in
Basically it appears all the heater servos run the same way. They get power and ground whenever the ignition is on, and the third wire is 0-12 volts. One could test it by connecting power and ground and giving power to the third pin[don't have the wiring diagram open in front of me] If it moves, when connecting disconnecting the third pin, the servo is good, back track to controls[heater pot etc]
The heater only boxes have the belt, I don't think the ac boxes do.