Heater only blows cold air

Asked by Goodnightbrenda Nov 11, 2018 at 01:01 PM about the 1991 GMC Sierra 1500 C1500 SLE Standard Cab LB

Question type: Maintenance & Repair

I have a heater that is blowing cold air only.  The heater hoses are warm.  What
is going on?  I have checked the actuator it is working.

2 Answers
10

t3k answered 6 years ago

I would have guessed actuator. How did you check it? Here is another thread on the subject that you may find useful. https://www.cargurus.com/Cars/Discussion- t14310_ds538830

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30

Lithman answered 6 years ago

I had this exact problem with my 91 gmc sierra 4.2 L. I try to keep Alldata subscriptions for my vehicles and followed the diagnostic flow chart to no avail. I noticed that the inlet hose to the heater core was hot and outlet hose and heater core was cold. Pulled the heater core and found it clogged with a grainy/flakey brown substance that I'm not sure what it was, but I'm assuming it was black pepper. I flushed it out thoroughly and reinstalled it and now I now have heat. Hope this helps.

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