Truck Heater Blowing Cold Air?

I replaced the heater control for my 1998 GMC Sierra 1500, 2w/d, 4.3 eng. The fan works and the directional switch works, but there is still no heat. It just blows cold air.


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Bronze Answer Medal for All Time! 242 Answers
November 15, 20171 found this helpful
Best Answer

Our Tahoe was doing this. We added water to the radiator and it started blowing warm air again. My husband told me that if the water/anti-freeze isn't circulating that it will turn on but blow cold because it is not actually reaching the heater core. It was a simple fix. If that don't work then try the other suggestions.

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Gold Post Medal for All Time! 677 Posts
November 7, 20170 found this helpful

You could have a problem with the thermostat or the heater core.

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Bronze Post Medal for All Time! 105 Posts
November 8, 20170 found this helpful
  1. Check to see if your heater core is getting hot water from the radiator. If not you'll need to locate the valve that controls the flow of water. This could be stuck. Try opening the valve by hand.
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  3. Flush your heater core. It has air inside it and it can't function correctly. You'll also need to chair the heater core coolant.
  4. Check both heater hoses for heat. If there not hot check the bypass door it is probably opened.
  5. If all this is good and working, then more than likely it is your actuator motor that is bad.
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Silver Post Medal for All Time! 433 Posts
November 16, 20170 found this helpful

Thermostat could be worn out or the heater coil could be plugged.

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