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Old 11-09-2020, 09:57 PM   #1
Big70
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Heater not working on high

For some reason my heater blower works great on low med and then when you put it on high it shuts off. Like I've lost all power to it. Any thoughts? It's a 70 factory ac cab with every thing still in it.
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Old 11-09-2020, 10:27 PM   #2
Getter-Done
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Re: Heater not working on high

Here is and old Thread that covers most of the issues.
Hope this helps

Link:https://67-72chevytrucks.com/vboard/...e+hi+speed+fan











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Old 11-10-2020, 08:49 AM   #3
sick472
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Re: Heater not working on high

The high speed is powered by a separate wire that feeds a relay behind and to the right of the glove box. You may not be getting feed power to the relay, OR the speed switch is bad, OR the relay is not working (OR any combo thereof). The plastic connector at the back of the speed switch is known for getting extra hot and melting down, but this usually causes fuse issues.

There's a wiring diagram in this thread that shows what I am talking about...

https://67-72chevytrucks.com/vboard/...d.php?t=807883
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