The AC on my Sable doesn’t blow thru the front dash vents anymore. Cool air is blowing in from the two corner vents on the top of dash. It still seems to cool the car, just takes longer (much longer). what is the problem?
Probably a vacuum leak either in the heater control or the hose that supplies vacuum to it. There should be a vacuum hose that runs from the engine compartment through the firewall to the heater control in the dash. If this hose became disconnected or has a leak, the heater control will stay in the defrost mode. On most cars, the default setting is defrost so if you lose vacuum you still have the most important mode.