No Heat

Matt Vaughn

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Hello everyone and happy thanksgiving! I’m having an issue, I have1999 GMC Yukon with barely any heat at all, especially when driving. I have a brand new radiator from champion aluminum radiators, I think a 195 degree thermostat? A new heater core, and new temp mature control actuator, also new heater hoses all through out. The hvac box seems to be hot like there is flow in the heater core with hot coolant, but out of the vents to barely any heat and driving it’s honestly just cool. What am I missing here? If the heater control valve is stuck wouldn’t that not allow any coolant to enter the heater core?
 

454cid

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Hello everyone and happy thanksgiving! I’m having an issue, I have barely any heat at all, especially when driving. I have a brand new radiator from champion aluminum radiators, I think a 195 degree thermostat? A new heater core, and new temp mature control actuator, also new heater hoses all through out.

Ok, so barring a bad part, or hooking up the heater hoses wrong, you should be good, there.

The hvac box seems to be hot like there is flow in the heater core with hot coolant, but out of the vents to barely any heat and driving it’s honestly just cool. What am I missing here? If the heater control valve is stuck wouldn’t that not allow any coolant to enter the heater core?

Most GMT-400's don't have a heater control valve, if you mean a valve that controls the flow of coolant. The SUV's and maybe crew cabs got them. Most just have the coolant constantly circulating through the heater core. The heat is ajusted by directing cool and heated air, with a blend door. It's likely that your blend door is stuck pulling in cold air. I've never had to mess with my blend door, but others here have.
 

Vikingdude

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Blend door is a super common failure on these. Not only can the electronic motor go, but the gearset inside the little plastic case can jump/skip and take away your ability to change the interior temp. Someone on a facebook group had photos of the internals and a description of how to fix. Let me see if I can dig up.
 

Matt Vaughn

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Thanks for all the replies, I have confirmed that blend door isn’t stuck, I did replace the actuator with one from my gm dealer, and it operates with no binding, cooling system is full and completely bled of all air, I do indeed have the heater control valve since mine is an suv, I’m completely at a loss of what to do?
 

Intragration

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Have you checked the temperatures of the inlet and outlet hoses on the radiator? If everything else is working as you indicated, then it would seem to have to be the thermostat.
 

east302

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Hoses are installed correctly? In the photo below, the top one is from the intake, the lower from the water pump.

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At the bottom of the water valve, there is a spring-loaded plunger/shaft that moves up and down. When down, the butterflies are open. See if it returns to the down position with engine off. With engine on, see if it is down. It goes up (closed) with the temperature dial in the MAX detent to assist with a/c performance.

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The heater door actuator has a silver position indicator dial on it. See if it turns smoothly from one hatch mark to the other as the temperature dial is turned - roughly 11 to 1 o’clock positions. Might have to pull the glovebox and get creative to see it. That is the one that you replaced, right? Not the one by the gas pedal.

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And last, there is a plastic restriction built into the heater hose connector at the intake. @Schurkey could elaborate, but if it’s damaged then it could impact coolant flow.
 
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