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Old 09-28-2010, 07:34 PM   #1
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Suburban NT32C blows fuse after a few seconds

This furnace has seen very little use in 38 years.

I got it lit but it would not blow.

Pulled it out and found massive mud daubers nests in the fan- cleared that out and the fan spun freely.

fired it up and it worked perfectly for about 8 seconds.

then the fuse blew. the coach (72 Revcon) calls for a 7.5 amp fuse.

I bumped it all the way up to 20 amps and it still popped (don't try this at home)

any guesses?
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Old 09-28-2010, 10:02 PM   #2
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Fan bearing.

If it's that old and not working you really should just replace the whole thing. There have been explosions, see http://www.airforums.com/forums/f427...0ma-35151.html
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Old 09-28-2010, 10:16 PM   #3
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Quote:
Originally Posted by hertfordnc View Post
This furnace has seen very little use in 38 years.

I got it lit but it would not blow.

Pulled it out and found massive mud daubers nests in the fan- cleared that out and the fan spun freely.

fired it up and it worked perfectly for about 8 seconds.

then the fuse blew. the coach (72 Revcon) calls for a 7.5 amp fuse.

I bumped it all the way up to 20 amps and it still popped (don't try this at home)

any guesses?
Bad blower motor.

Andy
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Old 09-29-2010, 04:36 AM   #4
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Fan bearing.

If it's that old and not working you really should just replace the whole thing. There have been explosions, see http://www.airforums.com/forums/f427...0ma-35151.html

Replace it? Huh? I'm sorry, i thought this was the Airstream forum.

Seriously, the thing is pristine, very little evidence of wear or even use. I'm thinking the bugs did some other damage.
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Old 09-29-2010, 02:56 PM   #5
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The shaft rusts in the bearing area if it isn't used for a long time, and causes drag, so the motor draws more current, and blows the fuse.

If it's 38 years old you really should replace the whole thing.
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Old 09-29-2010, 03:08 PM   #6
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If it's 38 years old you really should replace the whole thing.
I'm not being a tightwad. I actually had planned on replacing it with a much newer Atwood.

But an RV appliance guy (marksrv.com) said that age alone would probably not wear out anything in the furnace and it has definately not been used much. The insides are mostly shiny. The baffles are free of rust.

The motor bearing is a good suggestion. I can just put power to the motor alone and see what happens.

Since i posted my question i've seen an actual schematic, there ain't much else it could be.

thanks
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Old 09-29-2010, 03:26 PM   #7
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::shrug:: Your choice. I've never been successful or seen anyone else succeed in making a lasting repair to a DC motor bearing. It is possible to work oil into them, or inject them with a hypodermic needle under the lip or the seal (or through it), and get some additional life out of them. I farm and had an older planter with an air metering system that used one blower on each row unit, and when the fan bearings went out yes I'd try to work some oil into them but it was always a temporary repair. I've tried that on heater fans in cars and tractor cabs too, again, temporary at best.

It is also possible that the motor has a shorted winding if it's blowing fuses like that. The only way to know for sure is to check it with a growler but nobody does that anymore, they just replace it if there's any question.

You can see if you can find a replacement motor. Maybe they're out there. That would be a lasting repair. With older motors it can be hard to find a match and also hard to remove the blower wheel without damaging it. Moral of the story is that you want to be sure you can get the blower wheel(s) off and the motor removed before you spend $100 or whatever on a new motor.

Good luck.
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Old 09-29-2010, 05:25 PM   #8
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I found a replacement motor for the heater in my 73 at PPl Motorhomes out of Texas. they sold me the gasket that would prevent carbon dioxide leaks into the unit as well. i was happy to refurb the heater . I was in a hurry and didn't want to modify the AS at the time. Had to go to a Rally. It cost me somewhere around 120.00.
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