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Old 12-02-2022, 08:32 PM   #1
JimKrieger
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Question Furnace Access

Furnace wonít ignite, so Iíve been learning about it and think I know want to do. The furnace on this 2006 3500RL is a vertically mounted Atwood 8535. My problem is that the removable vent panel to reveal the circuit board, sail switch, etc. is on the side just under the above floor and impossible to access. Manual says no need to remove furnace from RV. Has anyone faced this problem and is it only solved by removing the two hot air conduits, exhaust pipe and gas line to tilt and open it up? Problem with that - it then won't operate to do trouble shooting. Any experience out there with this vertical mount.
 
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Old 12-03-2022, 11:36 AM   #2
DQDick
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We've had the up and down mounted Atwoods on all of our Montana's and everything from replacing sail switches and fan motors to clearing the burner tubes and adjusting the ignition was all able to be done, from outside the rig, without removing the furnace.
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Old 12-03-2022, 01:36 PM   #3
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2019 3130re
My furnace cover is on the outside.
Furnace on the left, water heater on the right.
I made the exhaust vent cover to keep rain out of the exhaust tube.
Second picture, Cover removed (just 4 screws).
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Old 12-03-2022, 01:59 PM   #4
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Looks like your furnace is, as you said, under the upper floor but with no exterior access panel, only the single exhaust vent. By its placement on the door side of the trailer it looks to me that it would be fairly easily accessed by removing the wall in the basement. You still might need to remove the furnace to work on it, which makes troubleshooting more difficult. Definitely slower but will still work.

Before diving in to it can you explain, in order of events, exactly what it's doing and at what point it fails.

Ex: you adjust the thermostat to call for the furnace to provide heat. then:

1. Does the fan kick on?
2. Does the fan kick on and then attempt to light?
3. Does it light and then turn back off?
etc.
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Old 12-04-2022, 04:13 PM   #5
JimKrieger
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Answers to all the great questions:
My vertically oriented furnace is only accessed via the basement with circuit board, etc. facing and near the floor above and next to the outside wall which has no access panel. The RV is on shore power. All 12 volt lights work fine. The gas/electric refrigerator works fine. The gas stove quickly ignites. All AC outlets and lights work fine. No fuses are blown and no circuit breakers are tripped.
(1) I set the furnace for a very high temp. (2) The fan comes on and stays on. (3) I then hear what I assume is the gas solenoid after about 15 seconds. It clicks once but there are no repeated clicks of the igniter. (4) About 15 seconds later, the gas solenoid clicks again. (5) About 15 more seconds and the gas solenoid clicks again. (6) The fan then shuts off and doesn't allow to come on again until some longer wait time passes. (7) I go to the outside exhaust and faintly smell gas. To me, it seems the ignitor never gets power. I wouldn't expect dirty igniter electrodes to prevent its clicking. My untrained guess is for a bad igniter, limit switch, bad sail switch or circuit board. If I have to remove the whole unit, I'll clean it and replace all but the igniter to try to avoid having the hassle of removing the furnace from the unit and disconnecting/reconnecting all the ducts again. I'm in South Texas for some months, so only need the air conditioner which is working well, thank goodness.
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Old 12-04-2022, 05:44 PM   #6
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Thanks for the update.

First, it's most likely not the sail switch. If it were then there would be no attempt at all to try to light. The fan would blow then shut off.

With the gas valve apparently working (smell of gas present) and no sounds of ignition, then my guess, like yours, would be the main board and/or ignitor. I'm not sure about the older furnace but on ours the ignitor is part of the main board. Do you have the original paperwork for the furnace? Ours came with a helpful parts list with check marks on the parts relevant to our furnace. That might tell you about the main board and ignitor. If you can locate the model number for your furnace you might also find what you need online.

Given the added difficulty of having to remove the furnace to service it you might also spend some time watching YouTube videos on RV furnaces. There are some helpful ones out there that can also help to identify the issue by the symptoms it's displaying.
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Old 12-04-2022, 06:07 PM   #7
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Quote:
Originally Posted by jsb5717 View Post
If you can locate the model number for your furnace you might also find what you need online.
From the OP's original post: "The furnace on this 2006 3500RL is a vertically mounted Atwood 8535"
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Old 12-04-2022, 07:24 PM   #8
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Quote:
Originally Posted by Joint Venture II View Post
From the OP's original post: "The furnace on this 2006 3500RL is a vertically mounted Atwood 8535"
Ah, good catch.
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Old 12-04-2022, 07:35 PM   #9
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If it were me I would pull the furnace and pull out the main board. Look online for a matching one. The main boards seem to be about the same and are fairly generic. Just check for general specs and compatible connectors. I would try to get a Dinosaur brand board if you can find the match.
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Old 12-04-2022, 08:05 PM   #10
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My 2955RL has poor access as well to the furnace. No outside access door and seems to be installed much like OP's furnace. Would it be feasible to install an access door for easier access in the future, much like the pics show above for the 2019 3130RE. Trying to be proactive rather then reactive here.
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Old 12-15-2022, 01:17 PM   #11
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Epilog. Removed all screws anchoring furnace to floor and was able to partially extract the unit without disconnecting gas or electricity. Turned on the thermostat and the furnace ignited and worked normally. Guessed that the movement may have jarred a failing sail switch back into service, so replaced that. Did some cleaning, re-mounted the unit and it has continued to work. Apparently on my furnace, a failed sail switch, electrically or from dirt, still allows the fan and gas solenoid to work and only prevents power to the igniter. Thanks to everyone for all the helpful suggestions.
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