You have a vacuum leak. The air flow is directed by doors in the HVAC system. The doors are actuated by engine vacuum through small plastic hoses. If there is a leak, this is what happens.
Check under the dash for broken or disconnected vacuum hoses. If you are lucky, with the engine running, you may hear a hissing. Also, if you find nothing under the dash, check under the hood. That is where the vacuum comes from.
Let me know what you find or if you have other questions.
Sunday, August 15th, 2010 AT 11:15 PM