Just recently I've noticed that my air will only blow out of one vent and will not change when I turn the dial. It is stuck in the Defrost/Foot selection. Heat and A/C work great when either one is selected. I called my dealer and he mentioned that it is the Blend Door Actuator. I don't believe him! Blend Doors mix air for the temperature. Please help, it's getting cold out and starting to snow. As a safety concern, I want the defroster to work full bore.! Thanks for any upcoming help!

 

It might be a vacuum problem. Check to see if you have any loose or damaged vacuum lines.

 

That does sound like an actuator to me. Had the same problem with a Chevy Van once except all I had was defrost vents and nothing through my regular vents. Really sucked in the Summer when running AC. Good Luck!