NO Heat and even colder air on deforst

Asked by Dec 20, 2013 at 02:52 PM about the 2002 GMC Sonoma SL 2WD

Question type: Maintenance & Repair

I have cool air coming out in heater mode.  I have already flush the radiator and also cleaned the heater cores.  What else can be causing this?

1 Answer

37,375

Stuck thermostat, air pocket, how did you test the heater core? Defrost blows cooler because the defrost uses the air conditioning to remove moisture from the air to defog the window quicker. Check the heater core lines for heat in both lines once the engine is up to temp. oif they are both pretty warm it could be the temp blend door isn't getting vacuum to it to open. If one line is hot and the other is cold then you have a blockage, if the engine is hot and both are cold then that's a serious blockage.

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