It sounds like a vacuum issue. However, the blend door is not responsible for air flow direction. Since the only issue is the 2 center vents, something has most likely come apart.
I have attached a pic for you to review. It indicates which vacuum hoses should be checked. Also, check to make sure the vacuum supply from the engine is good.
And yes, most of the dash needs removed. However, not the entire thing.
Wednesday, July 30th, 2014 AT 9:14 PM