Heater on my 01 GMC Sierra doesnt fully work

Asked by Weezer67 Jan 22, 2013 at 06:22 AM about the 2001 GMC Sierra 1500

Question type: Maintenance & Repair

Last summer, on cool mornings, I noticed that the heater didnt start blowing hot air once up to temp. Later in the day when it was hot out, I went to turn the temp to cool, it kept blowing hot air for a long time until finally cooling down like the control wasnt working. Now when I need heat, its -7 below today, I find its blowing warm air when its up to temp. It gets alittle warmer when i am driving. Any possibility its the temp. control  rheostat on dash panel?

3 Answers
177,545

tenspeed answered 11 years ago

On other GM products, the temperature is controlled by a stepper motor that controls a bypass door. The door allows air flow around the core when open. --- It could be that the door is stuck open. It could be that not enough hot coolant is flowing through the core due to a clog or low flow from a worn water pump.

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69,815

John answered 11 years ago

Lots of them also have a large debris "filter" going to the heater core. Seen quite a few clogged with symptoms similar to yours. Back flushing the heater core will clear the blockage if that is the issue. I mentioned this in a previous post and found a site with a handful of people saying the same.  http://www.cargurus.com/ Cars/Discussion-t2226_ds531377 http://www.pacificp.com/forum/ viewtopic.php?t=977 both links there, delete the spaces.

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