Mode door will not work

Hi all –

I am having a problem with the mode door on my 97 K1500. The actuator will rotate very slightly (just enough to say it moved) CW and CCW when the control knob is turned back and forth. The linkage is free, and this is happening with the actuator removed from the linkage. Before I spend money on an actuator or controller, I would like to be able to better determine where the problem is. So, I have two questions:

1 – There are three wires to the actuator motor. What voltage and polarities should I be able to measure on the actuator at a given position on the controller?

2 – I have the controller removed from the truck. At one end, is a ten position ribbon connector that I assume the actuator motor is connected to (the other connectors appear to be for fan speed). Where should I be able to apply 12v, and where should I be able to measure some varying voltage (that would appear at the motor, as in the first question).

I can probably replace both components for about ~$140, but like most people, I am trying to save every penny I can, so I would like to be sure that what I am replacing is actually defective.

Thanks in advance.

This is from my '98 C/K manual. Your '97 may be different.

At the motor:

Brown wire is 12v with key in run.
Black wire is ground.
White wire is signal from controller.

So, at the motor connector, I would check for a constant voltage change on the white wire as the control knob is rotated with the black grounded. The manual does not give any voltage values.

UPDATE Just reading some more in the manual and for the mode door motor to get power from the contoller on the white wire the fan has to be in one of the ON positions. Hope this isn't too late.