I have had issues last winter with the furnace cycling off and not cycling back on intermittently. This winter started that way but got to a point to where it would only run if you turned the thermostat off and back on again. Then a few days ago it would attempt to run but only for a minute. I pulled the 20amp fuse and turned off the battery disconnect and cut the four wires that are a ground, 12v+, 12v thermostat and another thermostat wire. I pulled the furnace out and checked the high limit switch and sail switch and they checked out good. I pulled the burner out and cleaned it and the gas burner tip. I'm pretty sure the board has failed and I ordered a replacement but I decided to put it all back together just to verify that burner will lite and actually work now and I have no 12v power supply. The 20amp fuse never blew and I have 12v at the breaker box. I did the 12v breaker reset button at the battery and still no power. I am just wondering if anyone can direct me in a direction.
Power loss to suburban sf-42q furnace 2017 landmark newport
- Thread starter Jgermany
- Start date
danemayer
Well-known member
I'm not sure what you meant by "cut the four wires that are a ground, 12v+, 12v thermostat and another thermostat wire." I'm also not clear whether you installed the new board or not.
But if you're not getting 12V at the control board, and you definitely have 12V getting through the fuse, it sounds like the wires maybe didn't get back the way they originally were.
But if you're not getting 12V at the control board, and you definitely have 12V getting through the fuse, it sounds like the wires maybe didn't get back the way they originally were.
I cut the 4 wires that supply the furnace. Checked the sail switch and high limit switch. Cleaned the burner and the gas nozzle and lightly cleaned the ignition strike with wool. Assembled the furnace back into the camper and spliced all the wiring back like I found it. Now I have no 12v supply to the board or thermostat wire with the thermostat temp set well above room temperature. Checked the 20amp furnace fuse and it's good and also checked voltage at the panel (fuse location) and it's good. I'm curious if the board powers the 12v for the thermostat as I can't seem to find a straight answer on the internet. And it seems that there is a break somewhere between the supplied 12v power from the fuse panel to the furnace. I am almost positive the board is bad and will have a replacement hopefully by Thursday. If all else fails I am comfortable with running a new 12v supply and ground directly from the fuse panel from a empty slot but I am not sure about the 12v supply for the thermostat.
danemayer
Well-known member
The thermostat connects to the air conditioner controls (perhaps a board on the air conditioner operated by the same thermostat as the furnace) and when the thermostat calls for heat, the control at the A/C unit closes the path between fuse box fuse and furnace control board, providing 12V DC to the furnace to start the furnace blower.
It's possible you have corrosion or loose connections at the A/C unit. But since you had 12V at the furnace before taking it apart, it really seems more likely that loss of 12V is either miswiring or bad connections at the furnace after putting it back together, or a blown fuse.
How are you verifying the fuse is ok?
It's possible you have corrosion or loose connections at the A/C unit. But since you had 12V at the furnace before taking it apart, it really seems more likely that loss of 12V is either miswiring or bad connections at the furnace after putting it back together, or a blown fuse.
How are you verifying the fuse is ok?
TravelTiger
Founding Texas-West Chapter Leaders-Retired
Are you sure you connected the wires properly again? I happen to have a photo of ours when recently doing work on it. The confusing part is that there are a few different green and blue wires. Look closely.
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JohnDar
Prolifically Gabby Member
One thing I’ve learned when doing wiring (especially on our rig) is wrap a piece of painters tape on both ends of a connection and label/code them so you can put it back together again. The wire colors are not always uniform from rig to rig sometimes.
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I took photos of everything and even cut them so there was a small piece of the furnace wire attached to the factory wire nut that was crimped. I'm positive that they are spliced the way they should be but I am not a 100% sure that I didn't short one out trying to get them taped before stuffing them back through the housing along with the gas line to remove the furnace cartridge. I worked a 12 hour shift yesterday and didn't get a chance to go up on the roof to pull the cover off the air conditioning unit tied to the furnace thermostat but hopefully I can get up there tonight and see what's up there.
So I finally got to the ac that is on the thermostat with the furnace and took it apart only to find a new issue. Seems that the hard start for the start run capacitor has crapped out and may have possibly damaged the board. I will save that project for another day. I installed the new board in the furnace and ran a dedicated +12v supply wire from a empty slot and added a 20a fuse, ran a new ground from a ground bar on the surge protector that is close by and ran 2 thermostat wires from a new digital thermostat installed in our bedroom ( opposite wall of the ac/heatpump thermostat). After everything was buttoned up we powered it up and it will run but has issues with the burner staying lit. If I cover the exhaust with something it works perfectly. Pulled it back out and disassembled the burner assembly and it has a couple of deformations with a hole in it. We just ordered a new burner and will give it a shot this coming Wednesday.
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I am having an issue with my Suburban SF-42Q furnace in my 2017 Big Country 3560SS 5th wheel. When we turn the furnace on and set it to a particular temperature, it usually fires up and stays on until it reaches the set point. When it reaches the set point it turns off. All is good. When the trailer cools off below the set point the furnace will not come back on. We have had it top the dealer 2 x and they replaced the circuit board. This did not fix the issue. We recently had a mobile RV repair out who also replaced the circuit board saying that it tested bad. He tested it and it worked, however 1 day later the issue returned. We have examined/test the sail switch. It is good. We have replaced the limit switch. We have installed a heat only thermostat manufactured by Suburban and bypassed the connection to the board on the AC to eliminate just one more point where an issue would occur. Nothing has fixed this issue. New to the forums and was not sure how to post a new thread...I am sorry if this does not belong here. Can any one offer any advise at all? On a Facebook Page for Heartland 5th wheels there was a lot of discussion regarding propane tanks needing to be full and both open. We have tried many different settings and nothing relating to the propane tanks appears to affect this. TIA....(BTW we have 2 AC units, the thermostat in the bedroom controls one, the thermostat in the living room controls the 2nd AC unit and the furnace, they are digital Domenic thermostats.)
danemayer
Well-known member
Hi wolerm,
I think on your rig the thermostat signals a control board located under the air conditioner board, which in turn sends 12V to the furnace to start the blower and fire the ignition. You might have an intermittent problem there.
Something else - a longshot - can occur if you fill the propane tanks in a warmer climate and then head to a cold climate. In warmer areas, the propane may include butane which doesn't work well in cold climates.
