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HVAC stopped working, help!



Hi there, I have been having an issue with the HVAC in my 2002 GMC Sierra 2500HD duramax w/ auto climate control. The blower would intermittently stop working from time and time, and sometimes would work fine for days. However just recently it stopped working altogether, right during a cold snap of course! 


After researching all over the net, I learned the most common problem was the blower motor resistor (or in my case the HVAC control module). So I replaced it hoping for a quick fix. But still didn't work. Ive tried disconnecting the battery and resetting the system, ive checked voltage all over and the control module is getting power but is not sending power to the blower. I bench tested the blower and it works fine. All fuses are good. I'm not sure what else to look for. I am at the point where I'm considering taking it in, but of course due to the holidays I cant get my truck in to any shop until the new year, if I haven't froze to death by then. Any help would be greatly appreciated! 


The picture is to show the type of control module I have. (Pictured is the old one, new one is identical)


Edited by RustyRipper
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This could be one of those, "keep bringing them back for a new one until you get a good one" deals. Parts are horrible today.


Before doing that though, check to make sure you're getting a 12v output to the fan at the fan wire at the module (may have to pierce a wire to do so, depending on how it's set up), and also at the fan, just to rule that out. If it's sending power to the fan, it's not the control unit.


Wiggle any connectors around as well - could have a bad, oxidized connection, or broken wire.

Edited by Jsdirt
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