Atwood 8535-IV blower non op

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New member
Aug 9, 2018
Hello all, first post here.
Im stumped, and growing cold by the minute here

Im in desperate need of help on my Atwood 8535-IV furnace
We are in MT and the temps are falling at night.

I have a brief synopsis of what I have done, and hope with your expertise , i might not turn into an IceCube...grin...
So is what has transpired so far:

Atwood 8535-IV
Blower was operational with no problems PRIOR to bench testing.

Pulled the furnace, as the furnace would not ignite.
Found the sail switch defective and replaced. The furnace bench tested fine thereafter .

Installed the furnace back to the RV, found that the blower SUDDENLY was nonoperative .

Checked all the fuses in the inverter none were blown , checked the reset switch on the blower housing, it was fine.

Went one step further...used the pigtail from the RV to bench test, and jumped the 2 blue thermastat wires, everything fired up, no problem.

The furnace is now bench tested and operational with a SUDDEN loss of thermostat control over the blower.

Im stumped, and getting cold.....brrrrr.
Again, Any help would be greatly appreciated
Thank you



Well-known member
Nov 22, 2010
Where our wheels take us!
Is there +12 volts on the red wire connection to the ignitor board?
Is there -12 volts (ground) on the yellow wire connection to the ignitor board?
Is there +12 volts on one of the blue wires but not the other at the board with the thermostat off?
Is there +12 volts on both blue wires at the board with the thermostat on?

Gary RV_Wizard

Site Team
Feb 2, 2005
West Palm Beach, FL
You need to get down to the level of diagnosis that Dutch suggests. Right at the furnace, not back at the 12v converter (an INverter has nothing to do with a furnace).

Basically the furnace requires two +12v inputs to function, a main power line from the converter/battery and a secondary one from the thermostat. The thermostat +12v is merely a trigger to start the ignition process; the fan and the controller board operate from the main +12v power line.

My Library article on Furnace Troubleshooting should help you understand how it works and where it can go wrong. See


Well-known member
May 7, 2015
Western Kentucky
Welcome to the Forum!

Sounds like the furnace is working fine after your service.  It is a thermostat issue.  Follow the suggestions above.  It sounds like a simple fix for someone with your skill set.

Note also:  An INVerter takes 12VDC from the battery and inverts and transforms it to 120VAC.  You probably have a CONverter which takes 120VAC and converts it to 12VDC to charge the battery.  Common confusion.


New member
Aug 9, 2018
:) :)
Many thanks to all who responded
A special thank you to Gary.
With a detailed email, and his patience and wisdom
I can now count myself as one of those that
will be warm

The problem as Dutch, and Gary pointed out was in the wiring
It was a very slow process, but taught me a lit in going
through it methodically .
Again many thanks, to all
Safe travels
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