There's is a small vacuum hose that is disconnected probably under the hood headed into the fire wall on the passengers side. Look for a small check valve to plug that hose into. It will be somewhere near or on the firewall near the rear edge of the hood, and it could be about the size of a stack of three nickels with a port on each side, or it could be the style with a built-in storage chamber.
That one is about the diameter of a quarter and about 1 1/2" long, again, with a port on each end. Your car might also use a much larger type of vacuum storage canister with the port for the hose. Vacuum-operated systems are spring-loaded to go to the defrost position when vacuum is lost. Your feet might freeze but the windshield will be clear.
Here are some vacuum diagrams (below) to help you see what needs vacuum. If you need to run a new hose to the control head to fix the problem.
Please let us know what happens.
Images (Click to enlarge)
Thursday, May 12th, 2011 AT 7:14 AM