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11-24-2015, 07:33 AM
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#1
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Senior Member
Join Date: Jul 2011
Location: AZ.
Posts: 569
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Suburban furnace won't lite
I have an 07 Voyage with residential Tru-Air and suburban furnace. When I turn to gas heat blower comes on for a few seconds and shuts down and burner doesnt lite. Coach temp inside is 58 so it meets temp criteria to let heat come on. Any Ideas?
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11-24-2015, 09:43 AM
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#2
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Senior Member
Join Date: Aug 2010
Posts: 455
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Quote:
Originally Posted by Dsrtrider
I have an 07 Voyage with residential Tru-Air and suburban furnace. When I turn to gas heat blower comes on for a few seconds and shuts down and burner doesnt lite. Coach temp inside is 58 so it meets temp criteria to let heat come on. Any Ideas?
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Same thing happened to me last winter. In my case it was the sail switch connection. Getting the cover plate off was the hardest part! Once the plate was off the sail switch connector was right in front of me, pulled it apart, cleaned it, put it back together and all has been good since
The sail switch is placed in the airstream of the fan, if the fan doesn't run, or runs too slowly, the switch won't close. which, in turn, will not allow the gas to turn on. In my case the dirty connection made it appear that the fan wasn't providing enough air and I had the exact same symptoms as you discribe.
Good luck
__________________
Stik
Full Timing since 2005
09 Journey 34Y, 2015 Grand Cherokee Toad
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11-24-2015, 02:06 PM
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#3
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Senior Member
Winnebago Owners Club
Join Date: Apr 2003
Location: Skiatook, OK
Posts: 2,548
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Dsrtrider, here is a link to a manual with a troubleshooting guide and sequence of operation.
http://bryantrv.com/docs2/docs/suburban_dd_nt.pdf
__________________
Grant & Pat
2014 Adventurer 35P
2021 Ford Bronco OBX
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11-29-2015, 01:26 AM
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#4
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Senior Member
Join Date: Mar 2015
Location: Newcastle, WA
Posts: 288
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I have had to replace the over temp limit switch twice on my furnace. The symptoms for failure of this switch on my particular model are the blower runs but no spark at the igniter. This is due to no power reaching the circuit to the gas valve and igniter because the over temp switch is open, it is a normally closed type thermo switch. Measure the voltage of the wires across this switch at start, if 12v is present the switch is okay.
My furnace is much older being a 1993 and when the over temp switch fails the blower will run forever or until the batteries die. They may have added a timer circuit on newer models to prevent this.
This is just one cause, but in the 22 year life of my furnace it is the only part I have ever had to replace. I am on my third temp switch now. Your home clothes dryer has the same type of thermo switch to prevent overheating. In fact I have replaced this switch on my home clothes dryer with the same symptoms, machine runs but no heat.
__________________
Kevin n Chriss
2015 Newmar 3103 Bay Star -The Pay Car-
1993 Fleetwood 28T Bounder -The Flounder-
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11-29-2015, 11:26 AM
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#5
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Senior Member
Join Date: Jul 2011
Location: AZ.
Posts: 569
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furnace wont lite
I have no power to sail switch? Sail switch has continuity when closed. Where is the limit switch located? Does power go to limit switch first then sail switch?
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12-01-2015, 03:36 AM
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#6
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Senior Member
Join Date: Mar 2015
Location: Newcastle, WA
Posts: 288
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It would be very helpful if you could provide the model number of your furnace, the circuitry does change over the years. I did some research and found out that they did indeed put a fan control on the board which shuts down the blower when there is no ignition. My older furnace does not have this feature, which is why the blower will keep running when there is no ignition. This illustrates one reason why the particular model number is important to share. We could both have the same problem with our furnaces but they will have different symptoms. Your blower will stop in the absence of ignition, mine will not.
On my furnace, the wall thermostat contacts close when adjusted above ambient room temperature. This will start the blower motor and if the blower reaches proper rpm the sail switch moves and closes its contacts. The next item in the circuit is the temp limit switch which is normally closed. If the furnace is too hot the temp limit switch opens causing an interuption in the circuit which shuts off the gas valve. When the temp limit switch is bad it never closes. When this happens no voltage is supplied to the control board which controls the gas valve and igniter.
There can be many causes that will lead to no ignition, it is a process of elimination. I was just pointing out the only item that has ever failed repeatedly on my furnace and it is easy to check with a volt meter.
If you have a schematic you can find the color of the wire which goes from the temp limit switch to the control board. Measure the voltage from the sail switch and the temp limit switch connection to the control board. If 12v is present the temp switch is okay. First however when the sail switch is in sail from the blower motor you should measure 12v across the sail switch. If the sail switch is good then check the next item in the circuit which is the temp switch on my furnace.
Your furnace could very well be wired differently than mine, perhaps the temp limit switch is before the sail switch rather than like mine after the sail switch. This is why you need to know the model number and have the proper schematic, to follow the circuit and observe at what point there is a failure. It is not easy or fun for most people to diagnose and learn how their furnace works. If you decide to invest the time to learn and understand the circuitry and components of your furnace, the next time you have a problem, that mysterious box won't be able to hide its problem from you very long.
Recently I had a problem with my generator not starting. Checking voltages I narrowed the problem down to a bad control board. This board has relays, which I checked first because they are electro mechanical switches and can fail with age. Sure enough there was no voltage passing through one of the relays. I purchased and replaced all three relays on this board for about $15 and the problem was corrected. This saved me 100's of dollars for a new circuit board, with the added benefit of understanding to certain degree how the contraption works.
Hopefully someone that knows more about your particular furnace will respond. I believe there are members that work on rv appliances for a living and have a lot more knowledge than I have.
P.S. You might have a better response if this thread was moved to a more general discussion rather than Winnebago specific.
Best of luck to you.
__________________
Kevin n Chriss
2015 Newmar 3103 Bay Star -The Pay Car-
1993 Fleetwood 28T Bounder -The Flounder-
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