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Pete, GMC Technician
Category: GM
Satisfied Customers: 24158
Experience:  14 years GM dealership technician and training.
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2001 GMC sierra p/u heater not blowing hot air, need help!

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problems with 2001 gmc sierra p/u heater not blowing hot air. had thermostat and water pump placed and still won't blow hot air

Hello,I will be glad to try and assist you with this,Welcome to Just Answer.

With the engine running and fully warmed up and the heater set on high heat locate the heater hoses going into the firewall (there should be two) feel both hoses,they should be hot or very warm to the touch both of them,if you have one that is and the other is allot cooler then the heater core is most likely restricted and needs flushed or replaced.

You can try flushing it by removing both heater hoses at the firewall and taking a garden hose and flush both inlet and outlet on the heater core at the pipes sticking out of the firewall.

If both hoses are hot and no heat you may have a faulty electronic actuator on the heater box inside the vehicle.The actuators control the temp and mode doors to control air flow direction and temperature output.

These would have to be checked/tested as well s the heater push button control unit to see which is faulty and needs replaced.

You can also try and recalibrate the actuators by locating any fuses in the under hood and dash fuse box that are labeled for the heater like HVAC/heater/ac etc.Remove these fuses and wait about 3 minutes,then reinstall them.Turn the ignition on and don't touch any heater controls and wait about 1 minute and then start the vehicle and see if the heater works normally then.

Let me know if you need anything else.

Happy New Year!

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