Home » Public Forums » GMCnet » Suburban SF35 burner cycles
| Suburban SF35 burner cycles [message #146188] |
Tue, 11 October 2011 17:17  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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We were out camping for the past week and needed the furnace running. Good thing I fixed it before we went as it was nippy overnight.
Previously it would start, then the burner would shut down. The local RV place charged me $350.00, replacing the sail switch, but it still did not work. I should have read the manual so I could take it right back and explain why his fix was wrong.. but alas i didn't. A new PC board fixed it.
Anyway, I hear the flame shut down every few minutes then relight again. I suspect the high temp sensor is causing this, but is this normal? The fan moves plenty of air when the furnace is opened, but it seems much less when closed up and forced out the vents. The vents and tubing are all open so it must be just the turbulent air not flowing smoothly.
It warmed the coach up in a few minutes. The little cube heater could not keep up as it was 10C inside and 4C outside the next morning.
If this is normal, then I shan't worry about it!
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Suburban SF35 burner cycles [message #146194 is a reply to message #146188] |
Tue, 11 October 2011 17:35  |
fred v
Messages: 999
Registered: April 2006
Location: pensacola, fl.
Karma: 0
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Senior Member |
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| RF_Burns wrote on Tue, 11 October 2011 17:17 |
We were out camping for the past week and needed the furnace running. Good thing I fixed it before we went as it was nippy overnight.
Previously it would start, then the burner would shut down. The local RV place charged me $350.00, replacing the sail switch, but it still did not work. I should have read the manual so I could take it right back and explain why his fix was wrong.. but alas i didn't. A new PC board fixed it.
Anyway, I hear the flame shut down every few minutes then relight again. I suspect the high temp sensor is causing this, but is this normal? The fan moves plenty of air when the furnace is opened, but it seems much less when closed up and forced out the vents. The vents and tubing are all open so it must be just the turbulent air not flowing smoothly.
It warmed the coach up in a few minutes. The little cube heater could not keep up as it was 10C inside and 4C outside the next morning.
If this is normal, then I shan't worry about it!
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the manual says it's OK for the burner to cycle once in a while but if it cycles continously something is wrong.
my furnace does this too and i haven't found the problem. i changed the high temp sensor but still did the same thing. i have not tried running it with the front panel removed. that should tell if it is an air flow problem. i suggest you try that and report back. i won't be using my coach for but will test this when i do use it.
Fred V
'77 Royale RB 455
P'cola, Fl
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| Re: [GMCnet] Suburban SF35 burner cycles [message #146198 is a reply to message #146188] |
Tue, 11 October 2011 17:40 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Bruce, make sure that you have full battery voltage. If you do not, the
blower will run slower, and the sail switch will do it's job, which is to
turn off the burner. Another quirk of the Suburban is that it likes to have
all four outlet openings used. If you only have 3 outlets, then the internal
temperature limit switch will turn off the burner too. What helps on a
temporary basis, is to open the doors on the sink cabinet when the furnace
is in operation and see if it continues to run. If it does, run another
vent from the 4th opening. Funny the stuff we learn the hard way.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Tue, Oct 11, 2011 at 3:17 PM, Bruce Hislop <bruce@perthcomm.com> wrote:
>
>
> We were out camping for the past week and needed the furnace running. Good
> thing I fixed it before we went as it was nippy overnight.
>
> Previously it would start, then the burner would shut down. The local RV
> place charged me $350.00, replacing the sail switch, but it still did not
> work. I should have read the manual so I could take it right back and
> explain why his fix was wrong.. but alas i didn't. A new PC board fixed it.
>
> Anyway, I hear the flame shut down every few minutes then relight again. I
> suspect the high temp sensor is causing this, but is this normal? The fan
> moves plenty of air when the furnace is opened, but it seems much less when
> closed up and forced out the vents. The vents and tubing are all open so it
> must be just the turbulent air not flowing smoothly.
>
> It warmed the coach up in a few minutes. The little cube heater could not
> keep up as it was 10C inside and 4C outside the next morning.
>
> If this is normal, then I shan't worry about it!
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
> Hubler 1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
> _______________________________________________
> GMCnet mailing list
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| Re: Suburban SF35 burner cycles [message #146209 is a reply to message #146188] |
Tue, 11 October 2011 18:35 |
Erv Troyer
Messages: 125
Registered: February 2004
Location: Lagrange, IN
Karma: 0
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Senior Member |
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| RF_Burns wrote on Tue, 11 October 2011 17:17 |
<snip> I hear the flame shut down every few minutes then relight again. I suspect the high temp sensor is causing this, but is this normal? The fan moves plenty of air when the furnace is opened, but it seems much less when closed up and forced out the vents. The vents and tubing are all open so it must be just the turbulent air not flowing smoothly.
It warmed the coach up in a few minutes. The little cube heater could not keep up as it was 10C inside and 4C outside the next morning.
If this is normal, then I shan't worry about it!
|
Bruce, in my years at Duo-Therm I checked out a lot of furnace installations, and I don't recall seeing ANY that would allow enough air flow to keep a 30,000 btu furnace to run any length of time without shutting off the limit switch, so yes, I would have to say that is "normal". The Suburban NT furnace was noted for having a very high duct temperature. I recall checking a Fan Coach trailer and we got a duct discharge temperature of 213 degrees F. at a floor register - imagine stepping on that thing with bare feet - can you say "busted ceiling and a sore head"?
If you are using the original duct layout of the Royale then you definitely will have this condition. Try to keep all ducts as short and straight as possible, and all registers wide open.
When I installed a Suburban NT-30 in our GMC I mounted it on a 4" high box, then attached the flex ducts to this box. I knew there would be times when we would need heat quickly, so I made the front of the box as a sliding panel. When we use the furnace I slide this panel about 1/2 open, then open the cabinet door to keep the heat from recirculating. This still pushes enough heat through the ducts to keep the floor warm at the front and rear.
Erv Troyer Lagrange, IN
74 Sequoia
reo43@aol.com
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