I have a 2000 gmc jimmy slt 4x4 and when I turn on myheater/air and choose (defrost,floor,front vent) ether still blow out every open instead of one. I was wondering what parts I should try looking at and replacing?
2 areas to check, vacuum and diverter plate. Leaking vacuum lines throughout engine compartment and under dash. Bad vacuum valve,(it positions the air diverter plate and changes air flow direction). And, a broken diverter plate.
