My a/c will suddenly switch to heat. Any thoughts on what could be wrong? My temp gauge is also not working. Related?

Asked by muhde Jun 09, 2013 at 09:52 AM about the 1991 Buick Roadmaster Estate Wagon RWD

Question type: Maintenance & Repair

I have a '91 Roadmaster Estate Wagon with 100,000 miles.  The temp gauge is not
working and without warning the A/C will suddenly switch and blow HOT air out of the
vents.
Are they related?
What could be the cause?

2 Answers
1,830

thedoctor answered 10 years ago

Does this happen when you accelerate. the "blend' door- hot/cold is controlled by vacuum if it switches to hot just when you accel its probably just a vac. leak, theres a vacuum reservoir, maybe ball shaped, maybe on the fender....check all the hoses. if you drive for a while then it switches to hot and stays there till you park for a while it may be a bad vacuum motor at the HVAC housing or a bad hot/cold switch

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