Problem with Atwood furnace

[DonMichUP]

Hi everyone. I have an Atwood 8516DCLP in my 1999 Alaskan Camper that worked wonderfully, but then all of a sudden stopped firing up. Fan would blow (common thing with the circuit board it has) but no ignition sound. I was going to trouble shoot the solenoid gas valve coils, and then the sail switch... considering that 75% of circuit boards are not faulty and replaced for nothing... and realized that I'd have to access the furnace from the inside of the camper so began taking cabinets and compartments apart. Good thing I did.

On the camper wiring that goes to the furnace, along with the thermostat wires, is a white wire that attaches to a yellow wire and then a plug connection. Alaskan says that the white wire is ground. From there the wiring goes to the furnace. The yellow wire's insulation was melted, exposing bare wiring. Good thing there wasn't a fire! I've included some photos. The furnace is only runs off the inverter from 120V shore power, no battery connection.

Any idea what might have caused this?? I'm at a loss. And after seeing that melted wire, pretty concerned. I see that the wiring was damaged after the wiring clamp, but not before that. So I 'do' wonder if that has something to do with it(??).
Don

[road-runner]

ScottG wrote:
High resistance at the molex connector.

I'm going to agree with this guess. As to why the insulation damage stops at the clamp, the wires get bundled tightly there allowing greater heat transfer from the yellow wire to the others. I've been having an ongoing high resistance problem with my water pump power running through a similar molex connector.

[DonMichUP]

I want to thank everyone for their input on this issue. Yeah Puddle Pirates, that's what I was thinking too. I finally got the furnace out and apart. NO easy task for any of it.

The gas valve coils checked out ok. The sail switch seemed to be ok. The ignitor seemed to be ok, but not sure how to test that really, nor how to test the motor. By what I've researched, even though there's no house battery, and I don't think it ever had one, someone could have wired an exterior battery or generator the wrong way at some point before I acquired the camper; reversing the hot and ground coming in to the camper. Either that, or, yeah, a bad plug. And/or maybe a bad motor even, as someone said.

Anyway, since the furnace is at least about 19 years old -- although I don't think it was used much as the burn chamber looks hardly used -- and since I have it all torn apart, I decided to replace some things because I sure don't want to have to go through all this again. So, I'm awaiting a sail switch, a motor, a field plug assembly, a limit switch, an exhaust wall gasket, and an electrode. I'll double check the tracing of the wiring going from/to the inverter in the mean time. But once done, it should be like a new furnace. I'll update once I get it all put back together and it's running.

[Puddle_Pirates]

I can’t add much else except I would take a real close look at the plug, to me that looks like it possibly could have somehow shorted in the plug. Or possibly a severely corroded plug connection.

Here’s hoping you sort it out.

[DonMichUP]

Yeah enblethen. The ground wire is factory, so I don't know. I'm going to need to go to an RV dealer for another molex connector and have them bench test my board, so I'll ask the RV service techs about this. Weird though how the wire is only affected about 8" forward (towards panel) of the connector and about 2" back (towards furnace) of the connector. And of course the connector itself. I'm wondering if the connector went bad, and/or a bad factory crimp that has finally manifested itself(?). Anyway I'll see what the techs say and let yas know.

[wa8yxm]

enblethen wrote:
That was an extremely overloaded conductor. I see that the pin going into the furnace is melted.
What does it look like inside the furnace?
I would do more searching to see what caused this overload.

I will second that and suggest installing a new wire.. A BIGGER WIRE to replace it... If it is ground you could just parallel.. but make sure it's at least 2x the diamater of the old wire.

With the wire damage I am assuming serious voltage loss. if that's the ground this means the Blower may not be blowing fast enough to sail the sail switch (The blower is the big power hog in the furnace) if the sail switch does not sail.. the control board will NOT light the furnace.. Safety thing don't you know.

If it lit the furnace without enough air it could melt the heat exchanger and then either 1: Start a fire or 2: You might go to sleep... .and never wake up (CO Poisoning) . I've heard of both happening with portable propane heaters (never an RV furnace though because of the safety interlocks)

[DonMichUP]

ScottG, that could be the problem, considering that the area affected was just before and just after. Question now would be why tho.

shastagary, I'll check those things as soon as I can get the darn thing out of the rig. It's not easy in this Alaskan Camper. I think I'll have to take apart some cabinet areas to do it. And they are glued at the joints, which means that I may have to re-fabricate those areas when putting it all back together. Fun fun :/.

[shastagary]

blower motor could be going bad drawing excessive current. bad bearings? and does not spin fast enough to activate the sail switch. or mud daubers nest in intake or exhaust?

[ScottG]

High resistance at the molex connector.

[DonMichUP]

Thanks, I'll check those things out. There's no house battery on board, I run things via 120V shore power to converter. Sometimes, I've raised the top of the camper using a 2000W converter that I have installed in my truck, and I've also frequently used a pure sine wave Yamaha generator for my power. The generator was never grounded. And I know for a fact that the camper also is not grounded to my vehicle.

[enblethen]

What it almost looks like is the entire ground of the rig was being carried by this conductor.
by this manual, it looks like the ground for the entire system went through the yellow conductor then went to true ground via the terminal mounted to the fan housing.
Open the 12 volt DC system and see if there is a missing ground to the battery and frame of the rig.
Check the yellow conductor going to the thermostat.
Check the black conductor to the motor.

[DonMichUP]

Yeah, pretty serious stuff enblethen. The furnace ran great last winter and this year to Alaska and while in Alaska on my month long trip. If that's the ground wire, weird that that would melt and not the hot wire. Alaskan Campers replied, "Don, The campers white wire is the ground. Sounds like somebody wired a plug wrong." After the conductor/plug, on the 'way' to the furnace, the wire is just melted a little. I added that pic above. No melted wire going into the furnace.

[enblethen]

That was an extremely overloaded conductor. I see that the pin going into the furnace is melted.
What does it look like inside the furnace?
I would do more searching to see what caused this overload.