Blower motor stays on

BB386

MEMBER
1993 GMC YUKON
5.7L
V8
4WD
AUTOMATIC
300,000 MILES

Replaced blower motor approximately one year ago. A/C only worked on high (it's hot here, so wasn't a priority to fix). Didn't use A/C for above two months, wouldn't kick back on when I tried. Replaced resistor, started blowing (no keys in ignition.) Started truck, checked all speed settings, heard relays click but no change in speed. Turned truck off and within a few seconds heard sparks/smelled smoke. Source= blower motor ground. Unplugged and grounded directly to frame, same thing happened. Swapped out the resistor with another new one, even though it looked fine. As soon as I plug in the ground, with truck off, blower turns on, sparks/burning smell. I'm stumped, please help!

Saturday, June 5th, 2021 AT 2:13 PM

3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

There are a number of things that will cause the ground to smoke and get hot.

The first is a dirty or faulty ground or ground wire. A short to ground will also cause this. Basically that is a faulty component that is supposed to "use up" the voltage but it is shorted internally and it does not use the voltage and so there is too much after the load and the wire gets hot.

If the blower was coming on even with the key off then I suspect you have a shorted relay which is what the control uses to turn the fan on and off.

To test this, we need to remove, test, and/or swap the relay with another.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

You have two relays, one for low and one for high. I would suggest testing each relay but this would be the likely thing that is causing this if you have moved the ground to the frame directly so it is unlikely to be loose or dirty.

Below are the wiring diagrams. Please let us know what you find with this. Thanks

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Sunday, June 6th, 2021 AT 3:23 PM

BB386

MEMBER
2 POSTS

Genius! Glad I didn’t mention that I had changed the relays too it may have confused the thought pattern. Changed the relays again today and no sparks, no more possessed blower. Thank you so much. New problem: A/C no longer cold. Think it’s related?

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Monday, June 7th, 2021 AT 4:09 PM

KASEKENNY

MECHANIC
18,907 POSTS

That is great that it worked out. Yes. If you would have mentioned that then I would have instinctively pushed another direction.

As for the A/C issue. We need to start a new post for that one. Simply because the heading for this one is a blower motor issue and others will not find an A/C issue under it.

However, if you can go ahead and check the pressures on the high and low side and then get a new post started with that info, we will get right on it. Below is a chart that will help with causes of pressure issues.

https://www.2carpros.com/questions/new

Thanks

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