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1990 Chevrolet Suburban Base 4D Utility

1990 Chevrolet Suburban
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September 19, 2012, 3:56 pm

Dustin H

Question: heater only works when set to 90

Not Working>> Lack of hot/cold air>> The heating system>> No>> heater only works when set to 90 degrees. Rear heat only works sometimes but only if set to 90. Turn it down to 89 and it blows out cold air.

September 23, 2012, 6:02 pm

Tyler O

Maybe an issue with the HVAC control unit/head or an issue with the heatercore, maybe the heatercore valve etc.

Hard to say for sure. A professional with the correct equipment should be able to retrieve the codes from the HVAC control module, which may point to the cause of the problem

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September 23, 2012, 6:17 pm

Dustin H

Tried a different head unit from out of my pickup. Does the same thing works at 90 but blows cold at 89. Gm service told me it was the recirc door actuator put a new one on and didn't work. Replaced the pass side blend door actuator and it still works the same. Every once in a while it will work correctly for a little while than goes back to only at 90. The AC compressor also kicks on even when set at 90.

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October 23, 2012, 9:10 pm

Tyler O

Maybe the interior temp sensor or the vent outlet sensor if equipped?

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