Home » Public Forums » GMCnet » Dash air/heat Blower Not Working - Blowing Fuses
| Re: Dash air/heat Blower Not Working - Blowing Fuses [message #371351 is a reply to message #371347] |
Sun, 21 May 2023 15:11   |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Ken, I disconnected the plug from the relay, and tested with a VOM. With it connected to the other end, at the switch, I have continuity to ground when the switch is in the high position. When the switch is down one notch, there is no continuity.
When I disconnect the plug from the switch AND the relay, there is no continuity on the orange wire. When I re-connect the plug to the relay, I get continuity to ground through the relay coil as you say. If I disconnect the plug from the relay, there is zero continuity to ground on the orange wire.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
[Updated on: Sun, 21 May 2023 15:29] Report message to a moderator |
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| Re: Dash air/heat Blower Not Working - Blowing Fuses [message #371352 is a reply to message #371351] |
Sun, 21 May 2023 15:15 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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So I've replaced the relay, and found no short in the wiring, and tested the amp draw on the blower motor (15.5 amps) . What's left?
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Dash air/heat Blower Not Working - Blowing Fuses [message #371367 is a reply to message #371352] |
Tue, 23 May 2023 15:55 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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It looks like I've finally figured out the problem with the help of my mechanic friend, Jim. I borrowed a similar switch, same prong layout and function, but with different brackets, possibly out of a Blazer or something, plugged it in, and went through the positions with power on. This time, instead of blowing the fuse, the blower came on at all speeds instead of just the lower three.
We took the switch apart and found the problem. The switch is a pretty simple mechanism with a nylon slide on the bottom, a copper plate on the top, with a spring in between. The copper plate is positioned on the nylon slide by a couple of tabs. One of the tabs was making contact with the switch housing, grounding it out and blowing the fuse, as evidenced by a small burned mark on the inside of the housing on one end.
The solution will be to not only bend the tab back a little but then to add a small piece of plastic to each end of the switch housing to act as additional insulation to prevent this from happening again. Evidently this switch is unique to the GMC or at least hard to find as it is listed on Applied's site as REALLY expensive, so making this repair seems to be the best solution.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Dash air/heat Blower Not Working - Blowing Fuses [message #371368 is a reply to message #371291] |
Wed, 24 May 2023 14:07 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Glad you got it. I had guessed that as your problem back on 5/13
“”The switch could be “coming apart” with the bent over tabs stretched if it’s the type I think it is. Or the phenolic material cracked? That could cause possible hot to case or full 12 to motor through switch instead of the relay. Best to inspect at this time. Also you could watch exactly which positiin caused the fault so you can observe on bench.””
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Dash air/heat Blower Not Working - Blowing Fuses [message #371370 is a reply to message #371368] |
Wed, 24 May 2023 20:41 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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JohnL455 wrote on Wed, 24 May 2023 12:07Glad you got it. I had guessed that as your problem back on 5/13
“”The switch could be “coming apart” with the bent over tabs stretched if it’s the type I think it is. Or the phenolic material cracked? That could cause possible hot to case or full 12 to motor through switch instead of the relay. Best to inspect at this time. Also you could watch exactly which positiin caused the fault so you can observe on bench.””
Yes, good job John. I had to see the inside of the switch to have that make sense to me. I eliminated all the other possibilities so it came down to the switch.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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