If your doors are operated by vacuum, they are normally spring-loaded to go to the defrost position when there's a leak or other failure of the vacuum supply. That's done for safety. Your feet might freeze but the windshield will be clear. Look for a small hard plastic vacuum hose under the hood. Be sure it's connected to the intake manifold and not cracked. There should be a small check valve too. You might have to temporarily bypass it to see if it's plugged or stuck.
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Thursday, May 24th, 2012 AT 10:06 PM