Atwood Furnace Problems

[pomology]

I have a problem with the Atwood furnace on my 5th wheel (2019 Montana High Country )

It's an intermittent fault, usually happening about once every week. In the middle of the night, usually around 1 or 2 am, we'll wake up cold with the furnace not running. If we turn the thermostat off and back on, the blower will come on, blow for around 30 seconds, and then turn off without even trying to light.

So after this fault:
1) The furnace doesn't even try to light after switching the thermostat on/off, only the blower comes on briefly
2) If I go outside and take the cover off, the red LED has the 1-blink pattern.

Here's the weird thing. If I take the cover off outside, and flip the little master on/off switch off and back on, the furnace lights back up immediately and continues to work perfectly until a week or two later when the exact same thing happens all over again. It is ALWAYS solved by taking the cover off outside and re-setting the master on/off switch.

Things I've tried:

1) I thought maybe the control board was bad. I bought a new one (Atwood OEM), but the problem stayed exactly the same.
2) Instead of going outside to take the cover off, I tried pulling the 12volt furnace fuse in the fusebox inside the RV and popping it back in. That does NOT fix the problem, the blower just runs for 30 seconds and turns off. The only way to fix it is to go outside, and re-set the master on/off switch physically located at the furnace control board.
3) I purchased a new sail switch and limit switch, since the 1-blink pattern says it's a "limit or airflow" problem. I will try installing those when they come this week and see if that fixes anything. But if the limit switch were bad it seems really odd that flipping the master on/off switch at the control board would fix it (for a week or two), while pulling/replacing the fuse inside the RV would not.

It's also interesting that it usually happens during the dead of night - i.e. when it's cold.

Any ideas what's going on or what may be the problem?

Thank you!
Randy

[A1RVTraveler]

pomology wrote:
Thank you gentlemen for your help! The sail switch recommendation appears to have fixed my problem!

Randy

Success at last.

[pomology]

Thank you gentlemen for your help! The sail switch recommendation appears to have fixed my problem!

Randy

[Mike_Tassinari]

Good afternoon Pomology.

Had the same problem with my Atwood furnace a few years ago. Drove me crazy and spent a pile of cast replacing parts that were probably good.

I bit the bullet and went to a friend of mine down on Cape Cod who does R/V repairs of all sorts.

It turn out to be the "High Tension" wire that supply's the electricity from the main electronic board to the spark/sense rod.

What made it worse for me as my furnace always worked fine in the moderate temps and fired up every time. When it got down to say in lower 3o ties or colder - sometime it would fire up - most times it would not.

Hope this helps
BTW - Everytime you shut off the on/off switch on the furnace - you are resetting any faults what may be on the board.

Mike T

[Chum_lee]

If none of the above fixes the problem, look carefully at all the internal wiring and connectors as well as the grounds. Check for good continuity at all the connections. Look for discolored wiring terminals and melted insulation on the wiring.

Chum lee

[pomology]

Thanks guys! That makes perfect sense. I've ordered part # 33082! I will update here on how it works!

Appreciate VERY MUCH all the input!!

Randy

[Old-Biscuit]

A1RVTraveler wrote:
The problem is with the sail switch bracket. Dometic/Atwood realized they have a problem and redesigned the sail switch and bracket assembly. The new bracket allows the sail switch to travel 1/16-inch farther.

What you currently see is intermittent sail switch operation. The fan motor starts but the circuit board is not getting a signal from the sail switch that it is closed.

The new part number is 33082. You need to change the sail switch AND the bracket. It is covered by warranty if you are in the 2-year warranty period.

Matt

THIS^^^^^^^^^^^^^

Sail Switch is not closing allowing DC to go to circuit board for igniton sequence
resetting On/Off switch allows circuit board to be reset ---clears the lockout condition

[newman_fulltime]

You either have alot of moisture in the line or a bad regulator. When it gets cold it freezes up looses pressure goes into lock out.You reset it after its built pressure back up.or has warmed up outside some and it works fine

[pomology]

Thank you all!

I will order part # 33082 to see if that will fix it. One question though - if the sail switch is the problem, why do you suppose that resetting the on/off breaker switch by the board RELIABLY fixes the problem, for a week or two, until it happens again? This has happened maybe 8-10 times in the last 3 months, and every time, resetting the on/off switch at the unit causes the furnace to immediately light, first try.

Answering the other questions:

1) I am on shore power - plugged in to 50 amps.

2) Does it light and then go out (yes/no) or does it not even try to light.
It does not even try to light until I reset the on/off breaker, and then it lights immediately

3) Do you hear the CLICK of the gas valve, the snap of the ignition system or not
No I do not

[wa8yxm]

Are you on shore power this happens or on batteries.

If on batteries. Have them (the batteries) tested because that is what the Atwood will do if he batteries are not up to the job of overnight .

WHY: The T-Stat calls or heat.. The blower comes on, When air flow is high enough a "Sail Switch" (wind powered switch) closes and the burner lights. If the sail switch does not close within a specified time the blower shuts off and it locks out. LOW battery means the blower does not blow hard enough.

Page 2: The blower motor could also be failing and running a tad slow.

If on shore power so batteires are full up then it's more complex.. Obeserve the furnace (remove outer cover) as the thing cycles and let us know what happens for more info.

Does it light and then go out (yes/no) or does it not even try to light.
Do you hear the CLICK of the gas valve, the snap of the ignition system or not

These are questions we need answered to diagnose.
Only took required is a screwdriver to remove outer panel

There is a "Switch" (Really a circuit breaker) in the outside compartment you can use to cycle it if the T-Stat is set high enough.

[A1RVTraveler]

The problem is with the sail switch bracket. Dometic/Atwood realized they have a problem and redesigned the sail switch and bracket assembly. The new bracket allows the sail switch to travel 1/16-inch farther.

What you currently see is intermittent sail switch operation. The fan motor starts but the circuit board is not getting a signal from the sail switch that it is closed.

The new part number is 33082. You need to change the sail switch AND the bracket. It is covered by warranty if you are in the 2-year warranty period.

Matt

[pomology]

Thank you! The furnace model is AFMD35131.

[mchero]

Might be a good idea to give us the MODEL of the furnace.
Sounds to me like the sail switch. On some of the Atwoods they have couple of crappy wire taps off of the control board. I know one of the blue wires that feed the sail switch feeds off of one of the two taps. While the furnace is running I shook/moved the wires in front of the plastic cover over the heat exchanger blower and the blower would stop.
That switch your referring to, I believe its a circuit breaker.
I'm sure others will chime in.

Thanks for the post.