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Old 11-17-2019, 08:06 AM   #1
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Furnace not working

I brought my camper to my upper Michigan hunting camp in early October, used the furnace and everything was fine. I returned a couple weeks later on a cold Friday night and the furnace would not come on. The next day the trouble shooting started and I failed to get it to work. I checked the fuse in the panel, replace the board on the furnace itself. I just hauled it back home to Minnesota where I can trouble shoot it more effectively. I don't "think" it's the thermostat, but I will try putting the original manual thermostat back in. I had done the digital hunter thermostat conversion years ago.

When I set the thermostat, to call for heat, I hear a click up in the relay board inside the AC enclosure, but the furnace will not start. I suspect the click is a relay engaging or trying to engage. I don't see the relay board available for sale anywhere.

I did a little trouble shooting with a service guy from the local RV place and we were pretty sure it was the board in the furnace. $170 part, installed, no change. Ouch.

My fear is that mice have chewed a wire up in the ceiling. I can tell there was some mouse activity up there. No chewed wires that I can see, but I could hear one (or more) up there when I pulled it out of storage this summer. I can't see any relationship to the wires in the AC wiring harness to the wires entering the furnace to be able to check for continuity.

Looking for ideas on what else to try?

I attached a few pics...First 2 are the furnace model & furnace board, next 2 are the relay board, and the last is the wire harness from the relay board.
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File Type: jpg IMG_0625.jpg (103.3 KB, 5 views)
File Type: jpg IMG_0634.jpg (80.2 KB, 4 views)
File Type: jpg IMG_0635.jpg (63.7 KB, 41 views)
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Old 11-17-2019, 09:35 AM   #2
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Ok "will not start" what exactly happens? Does the fan run?
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Old 11-17-2019, 09:36 AM   #3
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Ok "will not start" what exactly happens? Does the fan run?
No fan. No spark. No ignition. Just a click up on the relay board.
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Old 11-17-2019, 09:41 AM   #4
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No fan. No spark. No ignition. Just a click up on the relay board.
A strange development I forgot to mention....on the evening after replacing the board on the furnace (with no change), in the middle of the night the furnace fan turned on. No spark or gas though. I looked at the thermostat and I still had it set to call for heat. After waiting to see if the heat would come on (it didn't), I clicked the thermostat off and the next day, I could not recreate the fan coming on.
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Old 11-17-2019, 12:04 PM   #5
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One more of the whole works.
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Old 11-17-2019, 07:05 PM   #6
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Hi Scott,

You can try this to help rule out if the issue is with the furnace, or it is in the roof AC board or T stat.

You are going to jumper the furnace with a run signal. This will minic what the roof AC unit control board does. That click you hear in the AC unit, is the furnace run signal. It seems to be clicking, but you do not know if the contacts are making contact.

This great pic of yours.


You are looking for the 2 furnace wires in that bundle of wire nutted wire.

Here is the AC relay board. Look at the top left for the T3 and T4 push on terminals. The words Furnace is right above the terminals.


You are looking for the 2 blue wires coming out of the roof AC control box that is on T3 and T4. They are normally a blue wire with a white strip. And they go to a separate small thermostat wire cable to head down to the furnace. Make sure you do not get the solid blue wire that goes to the larger thermostat wire down to the room T stat.

You can see them here, (blue and white strip) but hard to see them on the terminals.


And the bundle outside the AC control box.


They attach to a separate small thermostat wire cable. One of those blue with white striped wires is + 12 volt power from the furnace. The other blue white striped wire is the run signal back to the furnace. To jump the furnace to run with no Tstat or AC unit board, undo the wire nuts from the AC control box on those 2 wires and wire nut them to togetter. Or use a jumper wire with alligator clips on them.

Take care to not touch one of them to any metal on the AC unit as one of them is hot 12 VDC and you will blow a fuse. As soon as the 2 wires connect, the furnace should take off. If it does, then the issue in in the Tstat, the AC control board or the wiring from the Tstat to the board.

If the furnace does not start, then you have issues at the furnace or the wire heading to the furnace. But you can at least separate out the 2 areas.

Here is another furnace post going on right now. He has an issue with the T stat, wiring or the AC board too. But his furnace now works. This is a long read, but may help you. It also talks to how to jump the furnace running right at the furnace to rule out the wiring from the AC unit down to the furnace. His furnace is an older furnace than yours, you have the upgraded furnace control board and no timing relay like he has, but they work close to the same.

http://www.sunlineclub.com/forums/f6...sue-19508.html

Hope this helps and let us know how you come out. Once you can verify the furnace works or not, it is then to next steps.

John
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Old 11-17-2019, 10:11 PM   #7
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Thanks John. When I jump the blues at the furnace, The fan comes on, ~15 seconds later the furnace sparks & ignites and burns until I remove the jumper. When I remove the jumper, the flame goes out and the fan runs for a bit longer ~1min, then goes out. The furnace will continue to run as long as the jumper is in place.

When I put a jumper on the blues up by the relay board, I get nothing from the furnace.

I suspect this tells me there is a bad wire between the relay board and the furnace. Bummer. That will be not be a fun one to chase a new wire!
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Old 11-18-2019, 08:50 AM   #8
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Hi Scott,

The good news, the furnace works, the AC control board has a good chance it works. Bad news is the cable from the AC to the furnace buried in the wall and ceiling may have issues.

Thinking on this, there "might" be hope for a simpler fix.

Have you looked at the connection area of the furnace where it joins to the thermostat stat cable that heads up the wall to the AC unit? I'm not sure how you floor plan has the sides of the furnace buried or not. If you look on the furnace control board side of the furnace, (the non gas line side) inside the camper, you will find the connection location of the furnace 4 wire plug to the thermostat cable. Maybe by chance, critters ate into that bundle which is more out in the open then buried up in the wall?

Here is this junction I'm referring to. This is on a 2005 T2363 but yours will look the same, just the cabinets etc. can be different.



The furnace unplugged


If the bad wires are there, that is an easier fix. If you cannot reach in to get to it, then you have to pull the furnace out and deal with it from the outside. Pulling the furnace is not that bad, just be prepared with new butyl tape to reseal it to the siding when you put it back in. Heat gun warm the black plastic flange and putty knife in behind it and the siding to break the old putty tape loose after all the screws are out. Just take care to not crack the plastic flange.

And if the problem is not at that wire bundle, well, maybe an easier run then trying to get a new wire back up into the AC unit, add a second Hunter T stat just for the furnace, ideally on an inside area wall. Then abandon the old cable to the AC unit. Don't know if this will work on your floor plan, just a thought to help spark ideas on how to get you up and going again.

Hope this helps and let us know how you make out.

John
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Old 11-18-2019, 08:58 AM   #9
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Yes I can at least put eyes one that bundle and don't see any signs of damage there. I'm going to start by running a pair of wires out the door and around the outside to the furnace and make sure it goes. Then I'll look to figure out how I'll route new wires to the furnace OR perhaps just run wire to a new separate t-stat just for the furnace. I'll follow up when the job is done. Thanks so much John.
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Old 11-18-2019, 09:02 AM   #10
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Quote:
Originally Posted by ScottK View Post
Yes I can at least put eyes one that bundle and don't see any signs of damage there.
Bummer

Quote:
Originally Posted by ScottK View Post
I'm going to start by running a pair of wires out the door and around the outside to the furnace and make sure it goes. Then I'll look to figure out how I'll route new wires to the furnace OR perhaps just run wire to a new separate t-stat just for the furnace. I'll follow up when the job is done. Thanks so much John.
Sounds like a plan. Hope the hunting and fishing ordeal goes smoothly. Darn critters,
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