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Old 02-14-2014, 08:59 AM   #1
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Furnace fails during freeze

So, we're camped at the Grand Canyon at a full hookup site. It's nice. We planned to stay 3 nights. It got cold at night and our furnace worked OK at first. Then it stopped working. When I turned it on, the fan would stay on about 15 seconds, then shut off. The propane did not seem to be lighting.
Night 2 got down to the 20's. We could see our breath inside the MH, but that's not the only indicator we had that it was cold. So, I tried it several times and no worky. Everything else on the propane system worked, so it was a furnace-specific problem. Between the Grand Canyon and Bryce, we stopped at a Walmart and bought a small space heater. It saved our bacon at Bryce, where it got down to -8 F. On the way home, we stopped in Las Vegas, and the furnace still didn't work, but it was not needed in Vegas. When we got home, I took the RV into the repair facility, and you may have guessed, the furnace worked perfectly. Of course, that cost me $125 to find out that there was no problem with it. Does anyone have an idea why this happened? Thanks for any help!
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Old 02-14-2014, 09:06 AM   #2
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Well you might have to go back to -8f temps to try this, unless you checked if other gas fired systens such as the HW or stove burners were working when the furnace was not. It seems like cold weather fuel supply issues to me, albeit -8F should not be a problem and if other gas appliances were working OK at the time, that would rule out the gas regulator. Just a thought but likely not the issue. Just wondered if other gas appliances worked when the furnace would not.
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Old 02-14-2014, 09:08 AM   #3
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The sail switch may have hung up. The fan comes on first to clear the fire box. The fan blows air across the sail switch and causes the gas valve to open. When the sail switch is bad or gets stuck there is no gas to light and the fan shuts down
This is not a major repair and most rv shops will know exactly what to do. Good luck.
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Old 02-14-2014, 09:12 AM   #4
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The sail switch may have hung up. The fan comes on first to clear the fire box. The fan blows air across the sail switch and causes the gas valve to open. When the sail switch is bad or gets stuck there is no gas to light and the fan shuts down
This is not a major repair and most rv shops will know exactly what to do. Good luck.
Thanks! That sounds promising. Can you give me an idea what the sail switch looks like and where I might find it in the mechanics?
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Old 02-14-2014, 09:18 AM   #5
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It will be in the air plenum. Looks like a switch with a metal tab hanging off it that hangs in the air stream from the fan. Google rv heater sail switch m
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Old 02-14-2014, 10:48 AM   #6
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The exact same thing happened to me (at Bryce also). I took to to be repaired at St George and it worked fine! I called Suburban and they said it was because of the elevation. Not sure about that. Someone else told me that some low elevation propane place mix in butane which works fine in lower elevations but not at places like the North Rim and Bryce. Sound plausible but no way to really test.
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Old 02-14-2014, 11:11 AM   #7
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Question: Did other propane stuff quit at low temp too?

First,, A Murphyism.. Furnace never fails when it's 80 in the shade. however when it is 8 in full sun, and there is no sun......
(Law of critical need, or Sod's Law).

Second: If you buy "propane" in the south, sometimes you get Butane, Here is the rundown

Butane has slightly more "heat" in it but not enough that you would likely notice,, And it costs less so the retailer selling it as Propane either passes on a lower price or pockets a higher profit.

Propane is good down to roughly the point where you do not need to ask "F or C" when hearing a temp.. That's -40 folks

Butane, roughly the freezing point of water..

Below that it will not vaporize and thus won't burn.
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Old 02-14-2014, 12:46 PM   #8
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If the propane tank was low (not empty - just low) there may not have been enough vaporization at that temperature to run the furnace while still having enough to run the water heater or a stove burner.
Attached Files
File Type: txt propane vaporization.txt (1.2 KB, 26 views)
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Old 02-14-2014, 01:36 PM   #9
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download a service manual for the furnace. do the diagnostics on it. check the propane regulator. take it off, and pour a half cup of denatured alcohol thru it, shake it out and reinstall it. also check the connection where the harness connects to the circuit board. clean the connector with some electrical contact spray. it sounds like a connection problem more than a propane problem, but cleaning the regulator never hurts.
when we are out traveling in below zero temps, which is often, i tape a heating pad to the bottom of our horizontal lp tank. if yours is vertical, just tape it to the side. set it on whatever setting you feel is good. i use the medium setting most of the time, but when it gets to minus 10 or lower,, i set it on high., and that should be sufficient to insure some lp vaporization.
btw, you cant stay warm when the weather is like that. carry an electric blanket, and good winter clothing. you will need it.
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Old 02-14-2014, 01:50 PM   #10
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I had the same problem but at sea level a few years ago. I found that my propane line to the furnace was exposed to the outside and was metal and had a slight dip in it. I wraped pipe insulation around it and I have never had the problem since and our temps last week got down to -1 degree.
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Old 02-14-2014, 01:53 PM   #11
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Hi Full.Monte,
You've done most of the diagnostics already. This is a switch or valve problem. Do not eliminate the regulator. It is a cheap (under $30) and easy part to DIY. At low temps, any moisture in the regulator, switches or valves will cause a failure. After the regulator, then I would go to the other items mentioned.

The furnace drinks propane like water going over Niagara falls. Other appliances can work fine, but if the regulator isn't working fully, the furnace will be the first appliance to tell you so.
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Old 02-14-2014, 01:59 PM   #12
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I can say on our 1982 PA the Thermostat wasn't level on the wall and the mercury level was off. Re-leveled it and has worked flawlessly since. Do you have a old thermostat that could be off level?
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Old 02-15-2014, 12:02 AM   #13
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Quote:
Originally Posted by wa8yxm View Post
Question: Did other propane stuff quit at low temp too?

First,, A Murphyism.. Furnace never fails when it's 80 in the shade. however when it is 8 in full sun, and there is no sun......
(Law of critical need, or Sod's Law).

Second: If you buy "propane" in the south, sometimes you get Butane, Here is the rundown

Butane has slightly more "heat" in it but not enough that you would likely notice,, And it costs less so the retailer selling it as Propane either passes on a lower price or pockets a higher profit.

Propane is good down to roughly the point where you do not need to ask "F or C" when hearing a temp.. That's -40 folks

Butane, roughly the freezing point of water..

Below that it will not vaporize and thus won't burn.
No, the other propane equipment worked at low temperature. I'll have to investigate that vaporization issue. Thanks!
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Old 02-24-2014, 07:43 AM   #14
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I can say on our 1982 PA the Thermostat wasn't level on the wall and the mercury level was off. Re-leveled it and has worked flawlessly since. Do you have a old thermostat that could be off level?
tb
Now, that's one I wouldn't have thought made a difference. We were parked pretty level, then we went to Las Vegas where we parked at a large campground that was level. When I get to a site like that, I often don't even put down the jacks. At Bryce, I didn't put them down simply because I suspected that they wouldn't retract with the temperature so low.

I thought that the coach-leveling was primarily to keep the refrigerator operating correctly. Does leveling also affect the furnace operation?
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