Heater not working

1994 GMC SIERRA
285,000 MILES
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DESERTRAT52
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The arrow on the Temp. control , Flash all the way across, won't adjust heat....
I have replaced the control unit and it does the same thing...
Is there some sort of relay to open the heater core ????? I'm stumped....
Nov 15, 2013 at 11:45 AM
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HMAC300
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see if the actuator i pointed to in the pic is working that may be your problem. Here are tow guides to help you fix the problem.

https://www.2carpros.com/articles/car-heater-not-working

and

https://www.2carpros.com/articles/replace-blend-door-motor

Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.
Nov 15, 2013 at 11:59 AM
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BOOPERIII
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I had to get a new actuator cost me $67.00 all fixed!
Apr 16, 2019 at 2:09 PM
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TRUCK000
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a/c doesnt get cold heat doesnt get hot. air sounds like it shud b blowin hard but its barely comin out.cant even feel it on low setting.can still hear it tho. changed thermostat and flushed core??please help
Dec 26, 2020 at 2:47 PM (Merged)
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JACOBANDNICKOLAS
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Actually, it sounds like there is a problem with the blend air door. This door is near the heater core. Its job is to turn one direction to allow the fan to blow air through the heater core and heat the vehicle, and the other direction is for the AC to cool the vehicle. Based on your description, it sounds like it is stuck in the middle. Therefore, you don't get good AC or heat and there is less air entering the vehicle.
Dec 26, 2020 at 2:47 PM (Merged)
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TRUCK000
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how do i get to this door and i have read something about a blend door actuator is that the same thing? it is a digital control if that matters.
Dec 26, 2020 at 2:47 PM (Merged)
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JACOBANDNICKOLAS
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It will be next to the heater core. The actuator is the device that moves the door. Yes, it can be bad.
Dec 26, 2020 at 2:47 PM (Merged)
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TRUCK000
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what about the blend door motor? and is there a way to tell which one it is. when pushing buttons on the control panel i can hear clicks coming from something near the heater core
Dec 26, 2020 at 2:47 PM (Merged)
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TRUCK000
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also will i have to open up the core housing to get to the door
Dec 26, 2020 at 2:47 PM (Merged)
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JACOBANDNICKOLAS
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Everything may be working but need adjustment. You need to try it while you check the part. If you hear it, chances are something is disconnected or out of adjustment.
Dec 26, 2020 at 2:47 PM (Merged)
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TRUCK000
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will i have to open the core housing to get to the door
Dec 26, 2020 at 2:47 PM (Merged)
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JACOBANDNICKOLAS
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Yes
Dec 26, 2020 at 2:47 PM (Merged)
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TRUCK000
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ok s its not the blend door. found its working smoothly. although there was a gadget unplugged. plugged it back in (into a box that looked like the actuator box in the fron but this was in back (motor side) ) after plugging that in the box mad a loud clicking noise until we unplegged it..any ideas
Dec 26, 2020 at 2:47 PM (Merged)
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JACOBANDNICKOLAS
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I would need to see a picture. It sounds like an actuator.
Dec 26, 2020 at 2:47 PM (Merged)