Changed only defrost

Asked by Oct 22, 2007 at 09:42 AM about the 1999 Chevrolet Astro

Question type: Maintenance & Repair

I recently changed the alternator in my van.  Since then, air will only blow from the defrost.  Blower fan, a/c, and heat all function.  Any assistance in helping me isolate what I've done to cause this would be greatly appreciated.

3 Answers


Alternator change is most likely not your problem. Sounds like you have a problem with the blend door inside the climate control system. Probably just coincidence that it happened at the same time as the alternator change.


the heating system on almost all vehicles defaults to defrost ( so you can see in winter) there is a very very good chance the vacuum supply line to the heater controls was broken kinked disconnected during alt r&r inspect under hood very close listen for slight hiss with engine running find vaccum leak find problem


It sounds like you knocked off the vacuum line that runs the heater box doors.

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