My ac is not blowing out of the center vents. It blows out of the sides fine, and the rear fine. Instead of blowing out of the center, it comes out of the defrost vents at the base of the windshield. What is causing this, and how can it be fixed? It hasn't been a problem with temps under 80, but if it get's much over 80, it becomes really hard to cool the car down, and all but impossible over 90. It'll be 96 deg tomorrow.