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Old 10-25-2020, 03:54 PM   #1
Wxman
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Furnace Woes Sanity Check

Hello all,
Atwood AFMD30121 furnace under the fridge in a Passport Elite 19RB. No exterior access.
This last trip worked fine the first day and a half and then tuckered out. Gas fine to all other appliances and no apparent issues with any electric. Turning the thermostat to off and then back to heat would generate the fan cycling on for the purge cycle, but no evidence I could discern of an attempt to ignite.
My reading of forum searches leads me to sail switch problem.
I haven't torn into it yet, but I think I will have to remove furnace to get to the switch. If so, is there anything else I should check first to maybe not need to remove the furnace. I would love an easy to reach reset button or on board fuse or the like.
Looking for the fairy tale ending.
Thanks
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Old 10-26-2020, 07:11 AM   #2
Wxman
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More info for anyone interested. There is a reset switch on top of the furnace unit that is accessible after removing the grill under the fridge. It had no effect on my problem.
I got the unit removed without major issue. Not a whole lot I can troubleshoot on the bench top. Everything inside appeared tight and clean. I removed the sail switch. It was clean and seemed to work smoothly in hand. Good continuity when switch was activated. I put the sail switch back in and connected fan to 12V. I got good continuity at the switch connections without fail. Basically convinced switch is not the issue. Limit switch or control board itself I gather are the next likely culprits.
I think I will buy both and install before reinstalling the unit and hope for the best. We want to take it out this weekend.
Any pointers for reinstalling the unit under the fridge. The exhaust lineup and seal appear to be the worry point for me. Can I/will it be OK to slide the unit back in and work the exhaust connection together, or should I/will I need to remove the exhaust port from the outside, install the unit and then install the exhaust port and reseal with ProFlexRV?
Thanks for any help.
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Old 10-26-2020, 08:45 AM   #3
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I cant help, but there are some youtube videos about servicing the heater.

https://www.youtube.com/results?sear...urnace+service
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Old 10-26-2020, 08:48 AM   #4
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BTW, what exactly is the function of the Sail switch?
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Old 10-26-2020, 09:59 AM   #5
Life-in-Him
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Sail switch determines there is enough airflow on the outside of the heat chamber to not overheat. There is also an over temp switch as safety. the sail switch on mine (replaced last week) is a very poor design. Atwood/dometic/Keystone know it's bad, have done nothing. replace the assembly. the old one can probably be seen to fail if you hold it horizontally (sail up & down) & gently blow on it. It binds in the sloppy grove since it's not pivoting on anything but it's imagination. It's just placed in the hole on the switch loosely. Testing the unit might be wise by tilting it up or down a few degrees. Mine worked a fewtimes after s dealer banged on it, but not till we replaced the sail switch did it work reliably. pull the inlet/outlet ports out, put the unit in. Then install the ports. be careful since you can strip out the frame where the screws go in. Be ectra safe. Double-tripple check for gas leaks. Use leak detector & don't use tape. Only use gas fittings & if damaged in any way replace them. Get a professional to do that part is the right way.
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Old 10-26-2020, 10:59 AM   #6
sourdough
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Quote:
Originally Posted by Wxman View Post
More info for anyone interested. There is a reset switch on top of the furnace unit that is accessible after removing the grill under the fridge. It had no effect on my problem.
I got the unit removed without major issue. Not a whole lot I can troubleshoot on the bench top. Everything inside appeared tight and clean. I removed the sail switch. It was clean and seemed to work smoothly in hand. Good continuity when switch was activated. I put the sail switch back in and connected fan to 12V. I got good continuity at the switch connections without fail. Basically convinced switch is not the issue. Limit switch or control board itself I gather are the next likely culprits.
I think I will buy both and install before reinstalling the unit and hope for the best. We want to take it out this weekend.
Any pointers for reinstalling the unit under the fridge. The exhaust lineup and seal appear to be the worry point for me. Can I/will it be OK to slide the unit back in and work the exhaust connection together, or should I/will I need to remove the exhaust port from the outside, install the unit and then install the exhaust port and reseal with ProFlexRV?
Thanks for any help.


Shouldn't be the limit switch. It shuts it down if it gets too hot but in your case it never tries to ignite if I understand correctly.
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Old 10-26-2020, 11:09 AM   #7
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Doing the tons of "researching" ive been doing since yesterday, i have read of people having not enough converter from the factory and when they went bigger, the furnaces would cycle normally. This was based on an Amazon review as im replacing my converter so dont hang me if its not helpful
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Old 10-26-2020, 11:48 AM   #8
Wxman
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Quote:
Originally Posted by Life-in-Him View Post
Sail switch determines there is enough airflow on the outside of the heat chamber to not overheat. There is also an over temp switch as safety. the sail switch on mine (replaced last week) is a very poor design. Atwood/dometic/Keystone know it's bad, have done nothing. replace the assembly. the old one can probably be seen to fail if you hold it horizontally (sail up & down) & gently blow on it. It binds in the sloppy grove since it's not pivoting on anything but it's imagination. It's just placed in the hole on the switch loosely. Testing the unit might be wise by tilting it up or down a few degrees. Mine worked a fewtimes after s dealer banged on it, but not till we replaced the sail switch did it work reliably. pull the inlet/outlet ports out, put the unit in. Then install the ports. be careful since you can strip out the frame where the screws go in. Be ectra safe. Double-tripple check for gas leaks. Use leak detector & don't use tape. Only use gas fittings & if damaged in any way replace them. Get a professional to do that part is the right way.
I didn't mention before, but I had read about the banging fix. I tried the furnace after removing the grill and did bang on it during the purge cycle to 'get the sail switch' to activate. Didn't work for me which is another reason (along with my bench testing) I am thinking circuit board instead of switch.

Should know more tomorrow when Amazon delivers the new Dinosaur board.
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Old 10-26-2020, 03:27 PM   #9
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Personally, While it's not fully installed, I would replace the sail switch, it could be just nfg. I have done this once. it is best to remove plate and tube of exhaust from outside. You will have to re-putty and seal after install has been checked and working well. Replace screws for that plate if any sign of rust.
I wouldn't bolt the unit down until you let it cycle once or twice. I would do this manually. Good luck
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Old 10-26-2020, 04:44 PM   #10
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I'm on my third sail switch in two years, all under warranty. It's an ugly design.

If you don't hear the "snap, snap, snap" of ignition attempts shortly after the fan comes on, it's like the sail switch.
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Old 10-26-2020, 07:30 PM   #11
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The problem is not with the switch it's the bracket that holds it. The bracket can interfere with the paddle arm movement and the switch doesn't make up. It's an easy fix to pull the switch out and trim up the bracket to give the paddle arm a little more room to move. Or you can get a new switch that has the new bracket design.

If you look at the new design for the switch bracket you'll see it's been modified to have a nice notch under the paddle arm.

The switch I'm holding is my original switch. You can see the area circled in red under the paddle arm and how it could interfere with the arm movement. The other picture shows the new bracket with that area cutout so the paddle arm has more range of movement.
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Old 10-27-2020, 03:45 AM   #12
Wxman
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Thanks, more to check out.
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Old 10-27-2020, 05:51 AM   #13
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Since your furnace is an Atwood did you look at the LED mounted on the control module and read the error code it flashed? This will usually steer you toward the issue area...

Your stock WFCO converter is more than enough converter for your RV... it’s not gonna cause furnace to not light off provided you have good 12 volts dc power..

I’d also measure across the hi limit sensor just to verify it has continuity when cold. Furnace won’t work if it’s open...

Sail switch in conjunction with hi limit switch complete circuit to allow DSI to fire and propane solenoid valve to open.
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Old 10-27-2020, 12:05 PM   #14
Wxman
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Done, working, happy for now.
Notes:
Except for the reset switch can't get to anything without at least disconnecting ducts and gas and sliding unit out from under fridge. I had to cut all wires to pull it out because they had been run behind some plumbing. I now have the bundle ran in front of that plumbing and could pull unit out without cutting wires if needed.

Single gas connection via flare fitting no issues getting it sealed back up.

No, didn't check LED code on OEM board. I started out thinking it was sail switch. When I got the switch out it seemed to test good out of unit. I put it back in and ran fan with a battery and the sail switch still seemed to test good.
I had read the OEM boards had bad reputation and ordered a Dinosaur FAN50PP via Amazon with next day Prime delivery. I couldn't find a sail switch or limit switch local to me or deliverable in time for our next trip. Also, they were both testing good as far as I could tell on the bench.
Since a new board was coming I removed the old board before looking at LED as I had not rigged up a way to bench test entire unit yet.
New board arrived. Had to modify slightly to get it to physically fit. Drilled out some brass standoff rivets in the mounting holes to fit my unit and had to bend the igniter connection 90 degrees.
I did modify the sail switch bracket after reading Steveo's post. I was getting good tests on the bench, but I could see how the alteration might stave off some issues.
Hooked everything up, including propane and ran through multiple cycles on the benchtop. Never a hiccup. All reinstalled now and has gone though several cycles without issue.

Happy for now
Appreciate the helpful comments.
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Old 10-27-2020, 05:52 PM   #15
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Glad to here you were able to get it working again.
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Old 11-01-2020, 09:41 AM   #16
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We have a dometic furnace. Tech replaced circuit board tested fine in truck and reinstalled in camper. It didn’t function again. End up being the fuse in fuse panel. Fuse had a built in relay which was faulty but fuse was good.replaced fuse without the relay furnace works fine now.
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Old 11-01-2020, 10:33 AM   #17
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We have a dometic furnace. Tech replaced circuit board tested fine in truck and reinstalled in camper. It didn’t function again. End up being the fuse in fuse panel. Fuse had a built in relay which was faulty but fuse was good.replaced fuse without the relay furnace works fine now.
Fuse with a relay ??? Do you mean a 12 volt circuit breaker that "looks like a fuse and has two tabs to plug into a fuse panel ???
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Old 11-01-2020, 10:43 AM   #18
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We have a dometic furnace. Tech replaced circuit board tested fine in truck and reinstalled in camper. It didn’t function again. End up being the fuse in fuse panel. Fuse had a built in relay which was faulty but fuse was good.replaced fuse without the relay furnace works fine now.
I've seen a rash of these failures in our Cougar group also. The auto resetting fuse is failing and causing the furnace to squeal due to low voltage we believe. Replacing the fuse with a new one or just a regular fuse has fixed the problem.
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Old 11-01-2020, 11:33 AM   #19
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I have a 2019 29RKS with the furnace under the fridge and no outside access.
We have been having, what sounds like, the same problem all summer. Furnace has been removed and reinstalled 4 times since May. Friday they re installed it and so far so good. My experience so far is that it could run fine for 2 weeks and then have the same issue.
I was told Friday that the sail switch would intermittently malfunction due to a design problem so they had installed a redesigned sail switch. I was also told this is a known problem with Atwood/Dometic.
Might be something to check out.
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Old 11-01-2020, 12:31 PM   #20
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Last year my furnace tried to start but wouldn't. Really didn't need it anyway. I decided to take it in for service this year thinking it might be the sail switch, but didn't want to pull the furnace out myself. They said the sail switch was fine, but the burner itself was rusted over. They cleaned it and said it works fine now. On the side of the furnace stamped in the metal it says "Hit Here". It doesn't say if you should use your fist or a hammer.
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