Atwood Furnace Blows Fuses

[Matt42]

I finally a chance to use my travel trailer, only to find that the furnace fan would come on for an instant, and then POP, the fuse would blow. I had replaced the motor last year, and all was well then. Then the new motor sat for a year in Arizona heat.



So far, my troubleshooting has been limited to this:

1. Check for bare wires or obvious problems. None, so OK.

2. Is electric igniter causing problems? No, so OK.

3. Will going from a 15 to a 20 amp fuse work? (I was watching VERY closely. ) No change, fuse still blows. So not the problem, maybe.

4. Will going to a 30 amp fuse work? Yes, this made the fan turn on and then immediately speed up. It was at the speed-up point where the 15 and 20 amp fuses blew. Maybe I am on to something. So I unplugged the 30 amp fuse.

5. I plug a 15 amp fuse back in, thinking that the thermostat had reset. It had not. So there was a spark across the fuse contacts, and I removed the fuse. Now NOTHING works.



Sooo, in addition to my original problem, have I fried the poor furnace's computer board?



It's an Atwood/Suburban 8531-III. I understand that this furnace is attaining antique or at least classic status. When it comes to propane fired devices that operate when my family is asleep, I am willing to rip out and replace the whole thing with an updated model.



Thoughts? Many thanks in advance.

 

[HBarlow]

Sitting in the AZ heat didn't cause the problem but did intrusion by mice or other critters cause mechanical binding of the fan motor?

What does the owner's manual specify for the correct fuse?

If you put safety at the top of your priority list and you have determined that your furnace is already old and becoming obsolete perhaps a new furnace is the best solution. You can find a new one from an internet discounter at a reasonable price and install it yourself.

Older RV furnaces can be rebuilt. I had one in an older but completely satisfactory Travel Supreme fiver I was using as my home away from home when I was transporting that had become erratic and unreliable. I pulled it out and left it at a local RV dealer when I was on the road for a week. They put new bushings in the fan motor and new parts in the burner and it still works great years later.

RV furnaces are simple.

 

[Matt42]

No mice!

We have six cats where we store the trailer, so no mice or other unwary rodents. Also, the trailer has no unsealed openings. There's no evidence of entry or corrosion. The old motor, long gone now, just had worn out bronze bushings. The new motor spun fine with 30 amp fuse.



The trailer manufacturer specified a 15 amp circuit fuse for the dedicated circuit. The Atwood nameplate tells me that it is an 8. 5 amp "unit. "

 

[Matt42]

More information.

The "nothing works" factor was due to the thermostat. It had vibrated down to one wire on the copper line on moving arm, and it just burned off during my silly experiments.

I have voltage to the red wire on four pole relay that powers up the fan motor, but no voltage to the blue wire on the four pole relay.

When I jump from the red wire on the relay straight to the motor red wire, the motor will run just fine and not make the fuse blow. When I try to make the system work "properly," the fuse blows. The only new part is the motor.