there is a reistor block behind the glovebox, basically there a are two resistors on it, one low resistance and one high resistance. on "1" the power goes through both, "2" goes through the high one, "3" goes through the low one, and "4" goes straight to the blower. Sounds like one of them is burned out. I forget what it looks like but i replaced it on a teg one time. easy fix.