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mmbrevo 11-20-2021 02:45 PM

Furnace trouble
Hey all,
So my furnace isnt working. Nothing trying to run no funny noises just nothing. The igniter board was corroded, so I replaced it. Still nothing. The fan is working and the stove works. I hooked the board up myself, is it possible to screw this up?

Argosy 11-20-2021 04:34 PM

Have you checked for voltage? Thermostat set low enough it's calling for heat?

MtCamper 11-20-2021 05:15 PM

You should hear the t-stat click on. Then the blower should start and run about 10 seconds, then the ignitor should fire. If no blower, I'd start with the t-stat and 12v fuses.

Old-Biscuit 11-20-2021 05:57 PM

1st you say " Nothing trying to run....."

then "The fan is working ..."

So if FAN starts then nothing else happens the first thing to check is whether Sail Switch is closing.
Fan comes up to speed then the airflow moves the Paddle that operates the sail MUST close in order for DC to go to Circuit Board for gas valve/spark for ignition.

Brand>Model of Furnace?

mmbrevo 11-21-2021 08:48 AM

So, the fan works if I set it to hi or low. But if I leave it set to Auto and turn on the furnace nothing happens.
I have checked fuses and they seemed fine.
Does the battery play a role in this? I have had issues with the battery where the fuse leading to the battery blows.
I have been using a heater that does a good job of keeping things warm. I turned it off til it got chilly, so Im sure it was cold enough to trigger the thermostat.
Im working and by myself so having a hard time scheduling someone to come and look at it. Temps are dropping into upper 20s for a couple hours at night but into the 50s during the day. If I leave a trickle of water running will this keep things from freezing up until I can get someone to look at it. Thanks to all for your help.

Old-Biscuit 11-21-2021 08:59 AM

"So, the fan works if I set it to hi or low. But if I leave it set to Auto and turn on the furnace nothing happens."

That FAN (Hi/LO) is the A/C Unit Fan ......not the furnace fan
Thermostat does not control Furnace Fan speed
*If T-stat Fan is not in Auto then A/C Fan will run when HEAT is called for

When HEAT is selected on Thermostat and inside room temp drops below the thermostat Temp Set Point then the Furnace should run
Furnace Fan comes on..1st/purge cycle then gas valve/ignition
Furnace Fan NOT coming on...then issue is with Thermostat or DC to furnace

Brand/Model of Furnace????

Year/Make/Model of RV??????

Brand/Type of Thermostat????

More details needed to help!

mmbrevo 11-21-2021 09:31 AM

This is an Atwood series AFS/AFM/AFL

mmbrevo 11-21-2021 09:42 AM

2017 Forest Rivers Wildcat TT

Daveinet 11-21-2021 09:47 AM

Most of these furnaces have a single blower motor with a fan on both ends. One side of the blower feeds the coach interior, the other side circulates air inside the boiler tubes. This side also has a sail switch that senses the air flow to make sure the air is moving before it will ignite. If the sail switch is not made, it will not switch on the gas a light the fire. Sooo.... here is a likely issue. Mud spiders love to build nests in the boiler exhaust vent. This prevents air flow, so the sail switch is not turned on. If this is the case, you need to pull the guts out of the furnace case and disassemble the boiler tubes around the fan, so you clean out the nest. Start with checking to see if the sail switch is being made. This should be labeled on the igniter board.

On Edit: I missed Old Biscuit's post. If the voltage to the fan is a little low, it may not spin fast enough to turn on the switch. Measure the fan voltage, then the switch. If the fan voltage is 12 volts, the switch should turn on, if it doesn't and the voltage is correct, then you likely have a mud clog.

mmbrevo 11-21-2021 09:58 AM

Thermostat is Dometic. How can I check voltage to furnace?

Ljwt330 11-21-2021 10:08 AM


Originally Posted by mmbrevo (Post 5992865)
Thermostat is Dometic. How can I check voltage to furnace?

Here is a link to Atwood Furnace technical manuals. You can look up the wiring diagram for your specific model.

Old-Biscuit 11-21-2021 10:20 AM


Originally Posted by mmbrevo (Post 5992828)
This is an Atwood series AFS/AFM/AFL

That is Three different models which have several versions within each model
AF...Atwood Furnace
S, M, L is small, medium, large.....referencing BTU ratings

AFS could be 12K, 16K or 20K
AFM could be 16K, 20K, 25K, 30K, 35K
AFL could be 35K, 40K

ALL are wired basically the same

12VDC from FUSED source (DC Dist/Fuse Panel) goes to an ON/Off --Circuit Breaker Switch (Located at furnace) then to the thermostat/from thermostat to circuit board etc

FAN must have DC and MUST Run before ANYTHING else can happen

Check for Blown Fuse in your RV DC Fuse panel
Then remove exterior furnace access panel and check for DC to/thru the On/Off --CB Switch on the furnace
(Should be a RED wire)
*IF fuse is Good the should be 12VDC ON red wire to switch.
Switch should be ON ---CB is manual Reset
**DC to switch also connects to BLUE wire going to Thermostat so that wire should have DC all the time also
(When t-stat closes the 2 blue wires connect and DC is sent back to furnace)

Here is manual for a AFM Series......wiring diagram on page 8

mmbrevo 11-21-2021 11:43 AM

Going to get a volt meter

mmbrevo 11-21-2021 03:39 PM

3 Attachment(s)
So gonna have to pick this up tomorrow.
However, I noticed a clicking sound when I turn the furnace on. Would this be the t-stat? Does this rule out a problem with the t-stat?

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