[angus10]

You say they move? How did you check them? By hand or by moving the switches on the dash? You can also check the vacuum hoses out under the hood (passenger side going into firewall) and trace them to the back of the control mudule, and there is one or more check valves on them. Sounds like the blend door is broke though. And the only way to fix it is to remove the whole heat/ac box from the vehicle. So check the hoses first. And I suppose you could have mice in there clogging it up if the truck has sat a while.