Atwood Furnace Fast Flashing Light

[jsb5717]

Buddy of mine has an Atwood furnace that won't run at all when the tStat calls for heat. The red light on the board flashes very quickly, non-stop...it's not one of the codes.

First thing that should happen when the furnace is engaged is the blower should spin up and clear the baffles. From there it should attempt to ignite if the sail switch is working correctly.

On this furnace, nothing happens. The red light flashes very quickly and the blower does not turn on. I can't find anything wrong. We've checked all the switches...all good. We connected 12v directly to the blower wires and it spins right up. At first we suspected the main board. We put in a new main board and have all the same symptoms, including the fast flashing light.

Without specific diagnostic equipment I'm out of ideas. Any thoughts or previous experience with these symptoms? Thanks,...

[chuckster57]

So try this:

Put 12VDC to the board, jumper the 2 blue wires together and tell me what happens.

[jsb5717]

Thanks, Chuckster. That may be tomorrow now but will give it a try. Is it possible there is a problem with the relay board at the AC unit?

My friend's 5er is a 2010 Holiday Rambler, maybe a Savoy 31SKT. The furnace is newer. It was replaced when they bought the rig 5 or 6 years ago. Still original AC with a wireless controller.

[jsb5717]

Update - did troubleshooting as Chuckster suggested. The drawing below is my understanding of what goes where.

1. We jumpered the 12v + and - from the trailer wiring to the furnace wiring per the drawing below. We confirmed that we had 12v at the red wire that plugs into the main board.

2. We then jumpered the blue wires. The red light flashed quickly again. However, the voltage at the red wire dropped from 12v to 4.XX v. Remove the blue jumper and back up to 12v.

3. We unplugged the blue wires from the sail switch and jumpered them. The red light went out but nothing happened.

4. At no time did the blower spin up, nor did we get any voltage at the other red wire on the main board that should power the blower.

We have the original main board and a new replacement main board...both with the same results.

Not sure what to make of it.

[chuckster57]

Start with the 4 wires that are connected to the trailer wiring:

One is 12VDC positive
One is 12VDC negative

Two are blue:

One is 12V TO the thermostat
The other is the return signal to the furnace.

If you have 12V going into the board, then jump the 2 blue wires at the trailer connection and tell me what happens.

You may end up pulling the furnace for some bench testing.

[jsb5717]

Thanks, but I'm not sure where you mean to jump the blue wires. Should I leave the furnace unplugged from the trailer and jumper as in my pic or should I plug it back together and jumper the blue wires somewhere else?

The furnace is already pulled out since no access from exterior.

[chuckster57]

If you supply 12VDC to the furnace using the two wires coming from the furnace. Then just put the two blue wires together.

Since the furnace is “on the bench” a simple test light would make troubleshooting easy. There should be a schematic on the furnace, simply “follow the path”.

Make sure the blower is connected correctly to the board.

[jsb5717]

isn’t that what I did in my drawing above?

[chuckster57]

Ok, let’s start over:

The furnace is on the bench, you have 12VDC at the 4 wire harness coming from the furnace. You have connected the 2 blue wires together and what happens?

[jsb5717]

Chuckster, here's the main board pic I referenced in our PM.

[chuckster57]

PM replied to

[CampNBrew2]

Please post results for us to keep in our memory banks (since I have an Atwood furnace )

[jsb5717]

I'm not sure how much help it would be except to say that troubleshooting requires looking at absolutely everything. Here's the last PM I sent to Chuckster

OK...sigh...problem solved. I told my wife this morning that it's got to be some stupid little thing, we just have to find it.

All along we've had the furnace out of the wall but have been using it's own plug as a power source since we were getting 12.5 volts at that plug. Today we took it into the garage and used a battery charger as a power source to do some testing and the blower kicked right on. So now we knew, after all that time trouble shooting the furnace, that the problem wasn't the furnace at all.

Back into the trailer and the trailer plug...nothing except flashing red light. Also, we discovered that pulling the furnace fuse doesn't kill power to the furnace. After testing the converter and the battery and finding that they were working fine, we pulled the 12v fuse block out of the wall to trace wires. We couldn't tell where the current trailer wire comes from or where the wire connected to the furnace fuse goes to. Made no sense. But we jumped off of the 12v fuse block to the furnace and it came right on. So, for now, we tapped into the wire from the furnace fuse and everything is working just fine.

If we hadn't used a different power source for testing we could have been scratching our heads forever trying to figure out why the wire that's been successfully powering the furnace for years had the voltage but no longer carried enough amps to power it...making us believe the problem was the furnace. Still a mystery. Also, why wasn't the furnace wiring routed through the fuse block. Another mystery but at least now it's fused.

Anyway, glad we got it figured out. It's pretty easy to fix once you know what's wrong.

[CampNBrew2]

Thanks that is still great knowledge. So you had 12VDC before but it wouldnt run? I wonder if that was just a signal wire from the stat?

[jsb5717]

No, it was a 4-wire plug. 12v, ground, 2 TStat wires. The 12v wire measured 12.5 volts on the meter but no longer would run the furnace, even though it’s been running it for years. It’s weird. Reconnect the 12v wire to a new source and it works like it should.

[JRTJH]

Originally Posted by jsb5717

No, it was a 4-wire plug. 12v, ground, 2 TStat wires. The 12v wire measured 12.5 volts on the meter but no longer would run the furnace, even though it’s been running it for years. It’s weird. Reconnect the 12v wire to a new source and it works like it should.

Does your 12 volt power distribution center (where all the fuses are located next to the 120 volt circuit breakers) have a fuse or a "mini DC circuit breaker" in the furnace circuit ???

There was a time in previous years when Keystone was installing a DC breaker that just couldn't handle the startup surge and would trip. Replacing that circuit breaker with a standard fuse usually fixed the problem with "my furnace won't run"....

On yours, if you do have the DC breaker in that slot on the DC distribution panel, I wonder if maybe the internal circuitry might be corroded or somehow burned or pitted, causing a high resistance and not supplying the full 13.6 volts to the furnace electrical connections under the refrigerator ?????

Just something to think about .....

[jsb5717]

Thanks, John, good thought but no, just the standard array of fuses. Just seemed odd that the 15A fuse marked "Furnace" didn't actually go to the furnace. The trailer is a 2010. My friends bought it used and the dealer they bought it from replaced the furnace in 2018 or 19 since the OEM furnace was failing within the year warranty they received. It's possible that they also ran new wires to the plug since there was a splice just above the plug in the power wires. It's not always easy to tell what someone else has done prior to ownership...or for that matter, what happened at the factory during construction. Oh well, it works now.

[jsb5717]

I'm stumped again. After getting this furnace working perfectly it now ignites and turns right off. But before jumping in with solutions, here's what we've done.

I have a lot of backup parts since I've had so many problems with our furnace so the furnace is basically completely rebuilt. Today in troubleshooting this thing I started replacing parts. Here's a list of what was replaced today:

• Sail Switch
• Main Board
• Limiter Switch
• Diffuser (old one is probably fine, just has a little rust on it)
• Propane valve
• Propane regulator - recently put on a new one but tried anyway just in case.

There's literally nothing left to replace, it's all new but continues to do the same thing.

The propane tanks were refilled last week. Has anyone ever received bad propane? Seems odd but I'm grasping at straws. FWIW the stove top fires right up. Any other thoughts as to why this thing won't stay lit?

Thanks...

[chuckster57]

Igniter/flame sensor.

[jsb5717]

Thanks, Chuckster. I didn’t replace that part. Question: That part looks like this pic. Is this type also a heat sensor?