Quote:
AC/Heat fan quits blowing when vehicle is accelerating up-hill
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This might be a bad check-valve that allows vacuum in the HVAC system to dissipate when the intake manifold vacuum is low (whenever there's a large throttle opening). I had this happen on a Volvo once and I could actually hear the HVAC blend doors move every time I put my foot down. I don't know what position the system defaults to without vacuum, but my guess would be defrost.