They use a vacuum articulated system to open/close the blend doors on these vehicles. Use a vacuum pump to check for leaks on the position switch, blend door diaphragms, and lines. Be vigilant.
April, 2, 2011 AT 9:04 PM
It sounds like a vacuum leak. Check under the dash as well as the supply line from the engine. If you are lucky, with the engine running, you may hear a hissing sound indicating where the leak is located.