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Heat not working when idling

I have a 2006 Buick Terraza and am having a problem with the heat. It only works when I’m moving. If I stop at a light or am just parked with the engine running, the air which was nice and warm, fairly quickly returns to outsisde air temp. If I’m just starting the vehicle up and let it idle in the driveway, the air being put out never warms up. The engine warms to a proper temperature, but the air coming out of the vents doesn’t. Any idea what would cause this and about how much it will cost to fix? Is it something I could possibly fix myself? Thanks.

First check the level of coolant in the radiator. Do it when the engine is cold. The radiator must be completely full.

Assuming the cooling system is full, the problem may be in the “blend door” which controls the air temperature by diverting airflow through the heater core or the AC evaporator, or a combination, depending on the desired temperature.

Thanks. That could be it. I was told recently that I had a slow leak of coolant.

mcparadice is correct in first checking the coolant level.

Have you have any engine work lately that required the coolant to be at least partially drained?

If the coolant level is full I suspect you need to or need to have your service tech “burp” the coolant system. Older cars do not need this but newer vehicles sometimes need to belch. Sometimes there is a bleeder screw for this but on mine I simply pulled a small hose until the air was eliminated.