Hi, my '08 when set to Auto temp will all of a sudden start blowing thru the dash vents instead of the defrost & lower vents like it is supposed to. If I switch it over to defrost, no change. Temp stays the same. Dealer had flashed it a couple of years ago & it cured it for like 3 days. It rarely did it over the summer but now it is doing it pretty much every time I drive it & with winter here. afraid it will fail completely and won't be able to clear my windshield. Any ideas?

Doug