Atwood furnace blowing cold some time at night...

Mine did the same thing. Thermostat fixed it. YMMV.

FWIW, neighbor of mine had a slide in with (I think) that furnace and was having the same problem when they came down from Canada. Go to bed nice and warm, and sometimes would wake up nice and cold. They would turn the furnace off, then on, and off it would go.

I found the connection to the sparker was corroded. Once I cleaned that up, the problem went away. Good news is you shouldn't have to pull the furnace to get to it.

Mine had the same problem and after troubleshooting to no avail pulled out the igniter and found that the air gap looked like it had spread too wide, likely due to road borne vibration... I squeezed the gap back to 1/4", reinstalled and it has worked flawlessly for 2yrs now...after the reinstall, I called the Atwood tech line and was told that that was exactly the right fix and that the gap will occasionally get out of its spec width of 1/4".

When I heard the ignitor trying to light when it failed, it sounded funky. Not the steady ticking. It went tick tick...........tick. Then reset to ready.

I took the board into the local RV place and they tested it, said it wasn't resetting properly. I'll be ordering a new board from Dinosaur after the holidays.

I also ordered a Wave 3, so I'll be installing that for the winter. The drain on my lone battery was ridiculous with the furnace....

When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)

*: At nearly every step the control board is involved. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.

1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid, Clogged Gas Jet
4: .1: Bad ignition circuit (high voltage) on control board. .2: Points too wide (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.

* applies to all steps by the way So does bad wire/connection.

Note that low battries will cause it to fail in the night if not on shore power. OR
Not enough battery
Or if using solar power not enough panels.
Epically if running on sol

had the same problem. Turned out to be too much air to the burner which caused the flame to blow out. Does the flame sound rough, roaring a bit? If so, use your fingers to cover the burner air intake a bit at a time until the flame smooths out.
Then a little electrical tape is all thats needed.
Its just like adjusting the air for the water heater, smooth quiet blue flame, no roar or yellow tips.

I was lucky and was there during a failed relight. It tried three times, then just ran the fan.

So I'm guessing it could be the board, ignitor itself, or the gas valve limiting flow? Now what the hell do I do? I'm guessing for the price of paying someone to diagnose it, I can replace all three and have peace of mind?

Thoughts?

Chris Bryant wrote:
I would pull and inspect the burner.

I can try this, thanks.

I would pull and inspect the burner.

AllegroD wrote:
Cannot tell from your post whether this was duplicated while on shore power. Could it be that your batteries got too low for the furnace to turn on? Check your manual. I believe the Atwood 7900 Series says 10.5 and above.

I ws able to duplicate it on shore power, I verified the relay has 12.9 to it, and the thermostat is sending 13.1 or so to it when tripped.

Went out a minute ago, and it was blowing cold finally.

The board light was green (power), which means it didn't ignite. I did notice that a couple times this morning it wouldn;t light on the first try.

Normal sequence appears to be:

Thermostat trips, sends power to relay and board. Light turns green indicating power. 15 seconds or so later the the board opens the valve (light turns red), ignitor fires a few times. If burner lights, the light stays red. Or it will close the valve and light will turn back to green. Then will retry to light (change light to red, ignitor fires, etc).

I;ve read that the regular board will try 3 times then stop, continuing the blower.

So, either the ignitor is getting weak, or I need to adjust it? Or maybe propane flow is limited when cold, also making it hard to light?