[apstguy]

1: sounds like you shoud disassemble your ventalation system & clean the thing out.

2: Disassemble and clean again. Switch may be bad if it doesn't turn on at low or is hooked up wrong.

3: How hard is it to change from Hot-Cold on the slider? Mine is really stiff - if yours is easy, the metal rod is broken. If that isn't it, the heater core is clogged, or the linkage to the heat-cold door is busted. Hope this helps!