Fan Cycling with nothing turned on (no furnace or AC)

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FixRV

Member
Joined
May 10, 2022
Posts
6
Location
Warner Springs, CA
I have a 2000 Pace Arrow issue. Recently the house fans started to cycle on/off every 30 seconds or so. This happens 30 seconds after I turn on the Aux power, but AC or furnace are not running (they both work but are both off in this case). I suspect it's a loose connection, bad board or switch and the system thinks it needs to purge before firing up the furnace. Furnace and gas are off, so hard to tell where to look for this gremlin. Fan air feels strong. I've checked as many fuses and wire connections as I can find throughout the coach, but I haven't used a multi-meter to verify anything, such as switches in the furnace.

The cycling does not occur when the furnace is running. Ideas?

Thanks!
 

Kirk

Well-known member
Joined
Oct 30, 2005
Posts
2,764
Location
Full-time , Escapee
cycle on/off every 30 seconds or so. This happens 30 seconds after I turn on the Aux power, but AC or furnace are not running (they both work but are both off in this case).
By Aux power, do you mean when you plug into shore power or use a generator? The furnace only uses 12V-dc power from the batteries or the converter. If you have one thermostat that controls both the air conditioner and the air conditioner, it sends it's information to a control circuit board that is located in the air conditioner and that is what turns the furnace on and off. Does the furnace attempt to light?
 

FixRV

Member
Joined
May 10, 2022
Posts
6
Location
Warner Springs, CA
The rv power switches are for main (engine battery) and auxiliary (house batteries). So by Aux, I meant the house batteries DC system. No shore power at this time.

The furnace does fire up and run fine if I turn use the thermostat to call for heat. I forgot to mention, the furnace control board doesn't appear to have a status light. I don't know if this model is so old that it didn't have them back then or the light isn't functional (or perhaps too dirty!)

Furnace is Atwood 8535 IV DCLP
 

Henry J Fate

Well-known member
Joined
Jun 14, 2018
Posts
1,979
If it is the Furnace Fan, it should be obvious as there will be exhaust air coming out the exterior vent on the side of the rv near the furnace.

If that proves correct, disconnect the control circuit from the heater (thermostats) but keep power applied to the furnace control board for normal operation. If the fan continues to run endlessly, control board is very likely.

The idea here is to eliminate any and all controls that send a message to the furnace to turn on. Isolate the control board to prove that the board is turning on the heat with no command to do so.
 
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