heater problem

03 Pontiac vibe / heater blows cold air when driven slowly (or at idle) even when motor is up to normal temp. Blows hot air when driven on the highway. Temp gage worms up normal. Makes me think thermostat is OK.??? Doesn’t leak antifreeze. Heater core, bad circulation???

1 thought on “heater problem”

  1. This sounds like a vacuum issue to the blend door actuator. To be certain its not the heater core check to make sure both hoses are hot at the firewall. If they are both hot, the heater core and thermostat are fine. This is of course assuming you have already made certain the coolant level is full.

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