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Old 01-19-2020, 09:49 AM   #1
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Furnace stopped working.

Any ideas why my furnace stopped working? It has worked great for 2 seasons. We have an 2018 Isata 5 with suburban furnace.
A/C works in heat pump mode, but when I click the furnace button on, nothing. The furnace doesn't even try to run, doesn't matter how cold it is or what you set the temp.
Plenty of propane.
I cut power to everything (both 12V and 110V) waited, and then turned back on. Still nothing.
Check all breakers and fuses, all good.
It has worked every night for 2 weeks just fine. Then yesterday it's kaput. We've used the a/c heat pump during the day, and then switch over to furnace at night. So I'm suspecting an electrical issue or relay that's confused.
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Old 01-20-2020, 12:51 AM   #2
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Hi, know you said you checked fuses but you have to check them all as sometimes mislabled from a couple of years ago when we had a similar issue.

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Originally Posted by ACTFEL View Post
Since nothing happened when the thermostat/controller told furnace to come on--- implied switch/electrical/relay problem.

checked fuses F17 and F18 which are labeled Furnace 1 and Furnace 2; they were fine. note that these fuses supply power to the front and bedroom heating cooling/ac controls

From there the manual says there is an on/off switch in on the furnace
pulled cover see pictures. switch is there and was in on position.
cycled switch still did not work.

somewhat at loss, I did not see an easy what to test for power on the furnace control board. So I just ran through the 40ish fuses for the unit looking for one that said "chk" .

Found F09 which is labeled "roof AC" bad fuse swapped out and furnace works as it is supposed to. Not sure if we can reprogram the labels on the fuse panel. In any case worth making a note on your furnace manual if you have it.

thanks for all the helpful suggestions and info.

David
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Old 01-20-2020, 09:25 AM   #3
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Did you actually test the fuses, or did you just look at them? I always suggest testing them with a meter because I've seen many that looked good but were blown.

Did you look on the furnace to see if there's a switch that accidentally got bumped off? I've heard of that happening.

Also test for 12 volt power at the furnace.
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Old 01-20-2020, 10:04 AM   #4
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I had a similar problem a while back. In Kentucky, furnace worked fine. Next stop in Missouri, no furnace and temps hit -5F. Furnace was totally dead - did not even try to fire. Next stop in Arkansas, automagically, furnace was working again. Never did figure out what the problem was. Good luck...
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Old 01-20-2020, 10:15 AM   #5
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Quote:
Originally Posted by SailorSam20500 View Post
I had a similar problem a while back. In Kentucky, furnace worked fine. Next stop in Missouri, no furnace and temps hit -5F. Furnace was totally dead - did not even try to fire. Next stop in Arkansas, automagically, furnace was working again. Never did figure out what the problem was. Good luck...
OK we'll head for Arkansas. Maybe that will do the trick
I'm re-checking everything, I did pull the fuses and not just look at them.
On another thread, someone talked about a sail switch getting stuck. What's that?
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Old 01-20-2020, 10:26 AM   #6
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Here's a how to on one brand...

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Old 01-20-2020, 11:16 AM   #7
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Have you searched for a Suburban dealer near you? It doesn’t need to be a Forest River or Dynamax dealer. Your RV is a 2018, Suburban has a 2 year warranty.

In my case, I have an RV repair shop less than a 1/4 mile from my house. He is a dealer for all the major RV brand components and does warranty work. No dealer needed. These repair shops are also much easier to access.

“Suburban offers a 2-year limited warranty on its furnaces, with 3 year coverage of the heat exchangers. Warranties cover defects from manufacturing and are valid only for the original owner. Proof of purchase is required.”
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Old 01-20-2020, 11:22 AM   #8
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Well, I could call someone... but, for me that's a last resort... drives my wife crazy.
Thanks for the video; on my suburban furnace, the sail switch is in a different location. I can see where it's at, but can't figure out how to get to it. It's inside the squirrel cage, so somehow that comes apart so you can remove the sail switch. I had lots of dog hair everywhere else, so I'm guessing that's the culprit.
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Old 01-20-2020, 01:34 PM   #9
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Quote:
Originally Posted by jdebevec View Post
Well, I could call someone... but, for me that's a last resort... drives my wife crazy.
Thanks for the video; on my suburban furnace, the sail switch is in a different location. I can see where it's at, but can't figure out how to get to it. It's inside the squirrel cage, so somehow that comes apart so you can remove the sail switch. I had lots of dog hair everywhere else, so I'm guessing that's the culprit.
These R/V furnaces have no return air/intake filters so they certainly are susceptible to things like dog hair clogging them up.

Here's a link to a Suburban furnace video that may give you some insight.
YouTube has lots of good information.
Just search.

https://youtu.be/l6F-3x2FsbY
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Old 01-21-2020, 11:06 AM   #10
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If the sail switch is bad: Shouldn't the furnace blower start and then shut down or just run with no ignition. Original post says furnace does nothing.
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Old 01-21-2020, 12:20 PM   #11
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If the sail switch is bad: Shouldn't the furnace blower start and then shut down or just run with no ignition. Original post says furnace does nothing.
Normally that's true, but if the sail switch is stuck closed the control board senses that and then nothing else happens. The blower won't run and it won't try to fire.
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Old 01-23-2020, 01:53 PM   #12
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My understanding is that the sail switch would only prevent it from firing, but the blower should still start. But I checked the sail switch anyway, was able to pull of the front of the squirrel cage. The switch is fine, so that isn't it. I did find that the furnace does operate if I bypass the thermostat and connect the two blue wires together. So it's an electrical problem upstream.
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Old 01-23-2020, 02:01 PM   #13
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Quote:
Originally Posted by jdebevec View Post
My understanding is that the sail switch would only prevent it from firing, but the blower should still start. But I checked the sail switch anyway, was able to pull of the front of the squirrel cage. The switch is fine, so that isn't it. I did find that the furnace does operate if I bypass the thermostat and connect the two blue wires together. So it's an electrical problem upstream.
If the furnace fires and operates by connecting the two blues wires together AT THE THERMOSTAT, the problem is the thermostat.

If you are jumpering the blue wires connection point AT THE FURNACE, you could have a wiring issue or a bad thermostat.
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Old 01-23-2020, 02:24 PM   #14
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Are you hearing the ignitor popping at any time? These units have digital spark ignition and the circuit board that controls it is of dubious quality. I had the same problem with a Suburban water heater that also wouldn't light:

http://www.forestriverforums.com/for...as-188117.html

This uses the same ignition system as the furnace, worth checking out.
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Old 01-23-2020, 03:46 PM   #15
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The furnace works when jumping the blue wires at the furnace. The wiring from the t-stat is routed through the a/c, and there is power there. But there's a voltage loss in the blue wire between the a/c and the furnace. So it's a bad wire. Maybe it was damaged during construction, maybe a mouse. Although I can find no evidence of a mouse.
I am not going to try to fish a new wire through the ceiling and wall, so it's going back to the dealer.
In the meantime, I am going to rig up a temporary thermostat to run the furnace for the rest of the trip.
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