Heater mixing door not working

The wifes 1997 Lesabre is not able to control the temperature coming through the vents. I can control where the flow comes out with no problem but the little motor that controls the mixture door is not working. I opened up the gearbox and everything appears ok. no cracked or broken gears but when I slide the hot and cold lever back and forth, nothing moves inside the gearbox. If I knew the pinout on the three wires going into the gear box, I could hook up a multi meter while moving the lever.
Here's a picture of the three wires (white, blue and brown) that power this gearbox. can anyone tell me what voltages I should see when I move the hot and cold lever back and forth?

http://img.photobucket.com/albums/v236/killforfood/IMG_5528-1.jpg

Also could somebody tell me how to test the hot and cold lever?

Thanks, Joel.