Question about 1997 GMC Sierra
Check your vacuum lines....i just had the same problem with my gmc Sonoma. Somehow a vacuum line came off after being to a mechanic...the mechanic couldn't figure out where the hose went so he plugged it with a screw and low and behold the heat switch started switching between window, dash and floor like it was suppose to.
Posted on Nov 01, 2012
It all has to do with vacums basically, when you turn the switch to defrost there is a hose that should **** a "door" so to speak over lettin the air travel through your defrost vents, and if your not gettin suction the in aint gonna switch over, and are you gettin it out of the floor vents?
Posted on Feb 11, 2009
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