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geezerb · 11-25-2013, 08:54 AM

A question for the Suburban furnace knowledgeable. My furnace does a decent job of heating the place but is short-cycling constantly. It will run for around 5 minutes and shut down and stay off for a period of time. Would this be a malfunction with the high temperature cut off? There is also two floor outlets in close proximity to the thermostat which might possibly cause the early shut-down .
I'm hoping for an easy fix because Winnebago put this furnace in a place that is well hidden from prying eyes and I don't relish the task of digging it out in the current weather conditions. (Yeah, I knew about it before it got cold but who needs a working furnace when the weather is delightful)

geezerb

chief02 · 11-25-2013, 09:06 AM

close or cover the vent near to stat and see what happens.

geezerb · 11-25-2013, 10:21 AM

Thanks. Just tried that with no results. I'm probably not getting out of digging that thing out after all.

alilly · 11-25-2013, 11:34 AM

geezerb,

I also have a Suburban furnace that is short cycling after about 2 minutes, it's a 40k btu IIRC. During all the testing below the 12v system was fully charged and the fan ran smoothly.

We spent two days at a repair shop trying to determine why. First the high limit switch was checked to be sure it was the correct "color code" for our furnace -it was. Green dot I think.

The high limit switch was checked and was determined to be the component that was actually shutting the furnace off.

The switch was replaced with a new one (twice) -still short cycled.

The outside cover as well as the covers inside (the one with the duct work attached as well as the return air vent) were removed. At this point there were no restrictions on the intake nor exhaust air. It still short cycled.

The tech hooked up their propane bottle/regulator and 12v battery, bypassed the thermostat installed in the rv and it still short cycled.

The furnace and the metal "shroud" it's installed in was removed and "bench" tested as a unit by the tech. It did not short cycle.

The fire box did not have any rust/dirt/rat nests or damage, and was a uniform dark color. It was hard to see any difference between mine and a new one.

The tech called Suburban and advised them of the problem and what testing had been done. Suburban asked that the metal tab the limit switch is mounted to be bent away from the fire box somewhat and (if not already) move one of the heat duct exits from the furnace so that the limit switch was in the direct path of the exiting heated air.

None of this helped and the tech said Suburban "said" it was safe to run the furnace in this condition -just expect to replace the high limit switch frequently.

I'm not happy with this situation but am at a loss as how to cure it. I watched all the testing as it was done, from start to finish and the tech was very thorough.

Sorry to be so long winded but hope this might help in testing for this problem.

Hope you find yours geezer...

alilly · 11-25-2013, 11:41 AM

Just a point: a normal furnace cycle would be the furnace running continuous until the thermostat shuts it off. A short cycle is were the furnace runs and the flame shuts off (but the fan continues to run) and then the flame starts again. It continues this "stair step" until the thermostat set point is reached.