The little white box you refer to is the controller to the hot/cold blend door inside the air plenum. If the white box is moving the little arm, but the lever to which it is attached is not moving, then the blend door is stuck in a particular position: Either hot or cold.
Try forcing the blend door lever to move, spray some penetrating oil. Whatever to make it move. Without damaging it.
If it is really stuck, you'll either have to remove the entire intake plenum to free the blend door, or be content with the temperature you are getting at the vents. Removing the plenum requires removal of the dashboard and lots of associated components in order to gain access. It's a huge complicated job.
Thursday, February 19th, 2009 AT 9:18 PM