2011 Acadia SLT2 with 40k miles. Traveling home on a 1600 mile trip and the only heat or air depending on the temperature would come out of center vents no matter if I turned it on defrost or floor. I tried all settings but no matter where I have it set the only air movement I get is from the center vents. Air pressure coming out of the center vents is good. Any ideas or suggestions before I take it to the dealer ? I searched the forum but could find nothing that helped me. Thanks BJT