I have a '91 Pathfinder SE 3.0L V-6 with Auto Air Conditioning. The air flow is solid to all other vents (side, center and floor) but not to the dash or side defroster vents. Blower motor is working fine (all speeds) and all mode switches seem to be working. When I select Floor/Defroster mode I get only floor. When I select Defroster Only mode I get some air out of all the other vents, but no flow from defroster vents. Any ideas what the problem could be and how to fix it?