hd10 heat always blows hot

[2dogbed]

Hello, been reading up trying to find a good solution to my heater always blowing hot. I have checked to make sure the selector switch (hot-to -cold) is moving and it is, but even with the heat off and the vents closed, it blows hot. Has anyone found a way to close the line with an additional switch or value. On this 101 degree day i almost cooked. Thanks

2019 hd10 Cab model 

[Andystoy19]

I have the same unit but so far no problem. The heater has 3 temperature components, the potentiometer (on the dash) which provides resistance changes to the heater valve actuator and the heater valve. The heater valve actuator should fully open and fully close the heater valve, if it does not it could be an actuator problem or a stuck heater valve. The actuator and valve are on the lower right side of the heater. Remove the 3 screws holding the cover to the dash and you should see the heater actuator it should rotate the valve about a quarter turn. If it does not remove the actuator (2 screws) and see if you can open and close the valve itself that should allow you to see if you have a faulty actuator or faulty heater valve. I don't know if they are sold separately. FYI.🙂

[Steelslinger]

You can get a shutoff valve and place it in the radiator line that supplies the heater core to stop the heater from getting heat. The other issue is making sure all the openings in the front wall are closed/taped/sealed off as it could be hot air flow coming through the wall from the radiator itself.