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Old 10-16-2013, 10:01 PM   #1
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Default 04 envoy hvac problems

I've recently had some problems with my hvac that I tried to remedy with no success. Not too long ago the blower motor would blow, then shut off on it'* own, begin to blow again, and shut off again. Often times it would even blow for a few seconds after the vehicle was shut off. After some time the blower motor quit working all together. After doing a little research online I thought there was a problem with the blower motor resistor. I bought a new one, changed it and the blower motor still doesn't work. So I disconnected the blower motor, removed it from the car and hooked it up to a 12v source and it worked. So my question is where do I look next. Please be specific because beyond what I've already done, I know very little about anything else in this area.

A few things that might be worth mentioning...The vehicle does have automatic temperature control. And the blower for the back seat still works just fine.
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Old 10-17-2013, 06:03 AM   #2
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Blower motors are DC motors. They have brushes inside that contact an commutator and are spring loaded to maintain contact as the brushes wear out. Sometimes the brush will either get hung up or wear completely out and no longer make contact with the commutator. This is a typical failure for blower motors on vehicles. I wonder while you were removing the blower, that maybe you bumped it just right and it started working again?? Or, do this test, verify you have 12v at the connector for the blower on HI, voltages will be lower on the lower settings.
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Old 10-17-2013, 06:37 AM   #3
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Looks like you need to find someone who has a scan tool that will communicate with the HVAC unit. It might have a trouble code that can send you in the right direction. It could even be a bad cabin air temp sensor but without the proper scanner it'* hard to diagnose. As far as the blower coming on after the car is shut off it is actually susposed to do this to dry the moisture off of the AC core to prevent mold. Most people don't notice this because they are usually out of the car before it does this. Does your control unit have the option to turn the fan on manually and the blower still won't blow?
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Old 10-17-2013, 07:06 AM   #4
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Mike1995, after I put the new resistor in and the motor still didn't work I disconnected the motor and checked the DC voltage that would feed the motor (I just checked voltage between the two wires feeding the motor). I had 0v no matter what fan speed I tried to run at. To be sure the motor was good, while I had it out of the car, I hooked it up to a 12v battery and it did run, so assumed the motor was good.

75 racer, I'm not sure if I can manually start it, but here is what I've expereinced since I've owned the vehicle before the blower stopped working...If I turned the heat or A/C, the blower would start blowing, and the automatic temperatue control would only control the amount of hot or cold air that the blower was blowing, but the blower always ran at whatever speed I set it at (the ATC didn't seem to control this). I hope that is clear enough. Thanks for the tip, I will see if I can find a place that has a scanner. If I remember right, AutoZone does that for free, right?
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Old 10-17-2013, 07:15 AM   #5
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The autozone scanner will probably only talk to the power train componets and not the body components. Perhaps a wiring diagram of the blower motor might be all we need of figure this thing out.
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Old 10-17-2013, 07:20 AM   #6
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That'* what I was thinking last night, but I couldn't find one online. Perhaps you could point me in the right direction?
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Old 10-17-2013, 07:47 AM   #7
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Old 10-17-2013, 11:14 AM   #8
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I'm trying your link but all I get is an error
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Old 10-18-2013, 01:26 PM   #9
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Got it fixed guys, thanks for the help. Found a wiring diagram online and discovered a fuse I didn't see when I checked them. The bad resistor must have blown it. Go figure.....
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Old 10-18-2013, 09:15 PM   #10
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Glad you got it fixed.
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