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Old 02-09-2019, 10:04 AM   #1
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Suburban furnace bench test fine. No lite in trailer

Hello. I have a 2006 all American by forest river 38í toyhauler and it has a suburban sp35f furnace in it. I have replace the control board and the propane valve on the furnace and still could not get it to lite while in the trailer. I pulled it out and bench tested it and it fired up perfectly. So I put it back in the trailer. Iím getting good 12v power to it and I can smell propane when it clicks trying to lite but not getting an ignition. Iím open to any and all advice. Thank you
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Old 02-09-2019, 10:12 AM   #2
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Check 12 v from battery, if it low it is possible not enough voltage for complete ignition.
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Old 02-09-2019, 10:18 AM   #3
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Quote:
Originally Posted by Flashflood394 View Post
Hello. I have a 2006 all American by forest river 38í toyhauler and it has a suburban sp35f furnace in it. I have replace the control board and the propane valve on the furnace and still could not get it to lite while in the trailer. I pulled it out and bench tested it and it fired up perfectly. So I put it back in the trailer. Iím getting good 12v power to it and I can smell propane when it clicks trying to lite but not getting an ignition. Iím open to any and all advice. Thank you
If you're getting good 12v power to it, I assume the blower is running fast enough to close the sail switch. Right?
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Old 02-09-2019, 10:42 AM   #4
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Yes, I turn the thermostat up the blower kicks on, 30 seconds later it starts to clicks like it’s lighting and then I smell a little bit of propane but nothing happens after that will go through that cycle 3 times and stop. The only thing I can think of is not enough power from the wires or my propane regulator isn’t letting enough flow from my propane tanks
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Old 02-09-2019, 10:45 AM   #5
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You've run a bunch of propane through your stove top? Bench testing the furnace opens the propane lines and fills them with air. I'm sure you're sure you've purged all that air out.
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Old 02-09-2019, 10:45 AM   #6
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Lite up you all burners on the stove to see if supply of propane is good. Are you on shore power or just battery?
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Old 02-09-2019, 12:27 PM   #7
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I would definitely have the trailer plugged in while doing these tests. Use your volt meter (you have one of course, right?) to make sure that you are getting proper voltage to the furnace. Check the voltage at the furnace while the furnace fan is running to make sure that you don't have poor connections limiting power.
As other have stated, make sure to bleed the gas lines by running your stovetop on high for a few minutes..
Make sure that insects have not taken up residence in your air supply and exhaust tubes that go through the wall.
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Old 02-09-2019, 01:44 PM   #8
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Check to see if you have full pressure coming thru your main regulator at your tanks.low pressure will keep your furnace switch from opening.
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Old 02-09-2019, 01:48 PM   #9
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I've seen the exact same symptoms twice, once on my 5er when I tested it before delivery (bought it used) and once on my next door neighbor's 5er.

Both times the problem was insufficient propane gas supply to the furnace. Even tho the stove and ovens worked well, it seems that the furnace takes MUCH more gas.

In my case, the problem was a bad regulator at the propane tanks. In my neighbor's case, it was a bad hose from his tank to the regulator.

Jerry
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Old 02-09-2019, 02:53 PM   #10
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Regulator

Quote:
Originally Posted by Flashflood394 View Post
Hello. I have a 2006 all American by forest river 38í toyhauler and it has a suburban sp35f furnace in it. I have replace the control board and the propane valve on the furnace and still could not get it to lite while in the trailer. I pulled it out and bench tested it and it fired up perfectly. So I put it back in the trailer. Iím getting good 12v power to it and I can smell propane when it clicks trying to lite but not getting an ignition. Iím open to any and all advice. Thank you
I had this exact situation. It would even light if I left the plenum cover (sheet metal that covers the heat exchanger) open. If I installed that cover, it would not light. It turned out to be a failed propane regulator at the tanks.

More detail:
The first thing the Suburban manual tells you to check is the propane pressure at the furnace. I ignored that because:
  1. The range worked okay/
  2. The water heater worked okay.
  3. I didn't have a gauge to measure 11" water column (0.4 psi)
After wasting hours of time trying other things, I finally spent 60 minutes building a gauge (picture on request) and discovered the regulator was out of wack. Attempting to adjust it caused a strong smell of propane, telling me three things:
  1. The regulator diaphragm had developed a hole.
  2. The life of a regulator really is ten years, just as everyone tells you.
  3. DW probably should have put a new shroud on the regulator and tanks when the old one fell apart.
Everything worked fine with a new regulator.

Larry
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