Can someone offer guidance with my furnace? Atwood 8940-III had burned out/seized motor. Tech replaced motor, sail switch and on/off 15a switch on unit. Now it runs, cycles on and heats great. When it comes to temp, flame cuts off but fan only slows a lot .... and board LED flashes pretty much constantly until I hit the off switch on the unit outside.I am guessing a relay, bad board, or maybe limit switch since that switch not replaced? Relay appears part of the board these days.Gotta hit road in two days, tues AM, so may not be able to get tech back out. Need assist in case of DIY on this part now that heavy lifting was done. Thanks for any guidance I can get.

I would say the Module board was damaged when the old fan motor seized and the Fan relay on the module board is sticking or burnt/pitted. Never had or heard of this type problem, but the odds are replacing the module board will fix it. Doug

the board has a time delay for turning the gas valve on/off.Also the fan delay for turning the fan off. Here is the link for troubleshooting you furnace. The first thing a all techs do is check all connections on the board also battery should be fully charged. http://bryantrv.com/docs.html

fischer wrote:the board has a time delay for turning the gas valve on/off.Also the fan delay for turning the fan off. Here is the link for troubleshooting you furnace. The first thing a all techs do is check all connections on the board also battery should be fully charged. http://bryantrv.com/docs.htmlGood suggestions, I will expand a bit:Sounds like the OP battery (s) are low or your converter/charger is not functioning.Fan slows = low battery! Fan may continue to blow because the controller does not have enough voltage to control the furnaces functions.Make sure that you are plugged into shore power, check your battery monitor if you have one.Plugged in after about 30 min your battery monitor should show that the battery voltage is high.This is not a charged indication as some believe... It takes hours to charge a low battery!Here is a direct link to the furnace section of the manuals provided by Bryants.http://bryantrv.com/docs.html#furnaceJim

The circuit broad has a 'blower power'........old timed delay relay incorporated onto boardT-stat calls for heatFan gets power thru circuit boardFan comes up to speed......sail switch makes up/high temp limit switch already closed...power goes back to board and then to gas valve/ignitorHeats blows......T-stat set point gets satisfied....t-stat contacts openPower to gas valve gets droppedFan continues to run until 'blower power' shuts downFan not shutting down.......Bad contact on connector at board. Pull/clean board contact surface with pencil eraser and check that pins in connector are not bentORbad 'blower power'..........NEW boardLow battery ,,,,,,,,,Fan would not start and if it did it wouldn't come up to high enough speed to move enough air to satisfy sail switch.Gas valve wouldn't stay open....heating wouldn't happen

Do you have the thermostat fan control set to auto?

Atwood 8940-III fan won't stop | Good Sam Community

bigfootford
Nomad II
Jan 10, 2016
fischer wrote:
the board has a time delay for turning the gas valve on/off.Also the fan delay for turning the fan off. Here is the link for troubleshooting you furnace. The first thing a all techs do is check all connections on the board also battery should be fully charged. http://bryantrv.com/docs.html

Good suggestions, I will expand a bit:

Sounds like the OP battery (s) are low or your converter/charger is not functioning.
Fan slows = low battery! Fan may continue to blow because the controller does not have enough voltage to control the furnaces functions.

Make sure that you are plugged into shore power, check your battery monitor if you have one.

Plugged in after about 30 min your battery monitor should show that the battery voltage is high.
This is not a charged indication as some believe... It takes hours to charge a low battery!

Here is a direct link to the furnace section of the manuals provided by Bryants.

http://bryantrv.com/docs.html#furnace

Jim
fischer
Explorer
Jan 10, 2016
the board has a time delay for turning the gas valve on/off.Also the fan delay for turning the fan off. Here is the link for troubleshooting you furnace. The first thing a all techs do is check all connections on the board also battery should be fully charged. http://bryantrv.com/docs.html
dougrainer
Nomad
Jan 10, 2016
I would say the Module board was damaged when the old fan motor seized and the Fan relay on the module board is sticking or burnt/pitted. Never had or heard of this type problem, but the odds are replacing the module board will fix it. Doug

Forum Discussion

Atwood 8940-III fan won't stop

About Technical Issues

Related Content

Atwood water heater problem

Atwood 8940-III-DCLP Furnace issue

Atwood furnace

Atwood Furnace

Atwood Furnace issues