1984 Winnebago Chieftain 22 Furnace

[Rodney Behrens]

Hi we have a 1984 Winnebago Chieftain with a suburban furnace, the furnace heats to set temp and shuts down. Then it starts to cycle on for 5 secs. then off for 5 secs. it does this around 5 or 6 times then shuts down completely until asked for heat and it repeats. Any help would welcomed. thanks, Rodney.   

[david craft]

Prolly got some residual heat in the heating element that is transferring to the fan switch in a delayed fashion that is causing it to cycle. Carbon build up, oversize pilot, weak fan switch, or possibly an expanded element that has too close of proximity to fan switch. Betting on pilot or carbon.

[Russell E Johnson]

Silly question time David, wouldn't this furnace have electronic ignition instead of a pilot light?

[brian leibow]

look at wall thermostat,what brand?is it original to mh or is it a replacement?there are adjustments that can

be made at the thermostat that may solve this problem.

[Rich Thomas]

I'm with Brian on this one, I have a suburban 20kbtu in my M.H. no pilot light, it's electronic like Russell mentioned. The PO had replaced the analog two wire thermostat with a Walmart digital unit that I think caused the timer relay to fail ( I'm guessing here but I think it was pulsing like your talking and spiked the relay coil ) anyway the digital unit failed in the middle of a Thanksgiving weekend camp out and I was able to get a new two wire analog thermostat from an RV sales that was open and replace it. All is right with the old Suburban now and I hope this is of some help to you.

[david craft]

That time delay circuit is about 20 seconds. If it was a thermostat it probably could no do the 5 second cycle through the 20 second delay. Im thinking time delay. Bypass the thermostat and just short the two blue thermostat wires. Let it cycle then break the thermostat wire connection and see if the time delay fritzes. I thought about my previous post after I posted at a later time and i was like..."was that an 84'". Not that old of an good old RV...yokes on me this time...lol

[Rich Thomas]

Hi David on mine it would click on then off repeatedly  just as though it was a normal cycle only abnormally short.  the coil inrush current and the spike from the collapsing magnetic field of the coil eventually burnt the coil wire into on the coil its self. I built a coil saver circuit to help the longevity of the coil but I have yet to install it. In my case it was a problem with compatibility or the failure of the digital thermostat. I didn't have any paperwork with the solid state thermostat but it was just as if it was calling for heat and as soon as it got it, it turned off again It wasn't an instantaneous ratcheting of the relay. Hope this clears the air so to speak.  By the way touching the two wires together is exactly how we heated the camper until the RV store opened.and is a good diagnostic tool.

[david craft]

wow...OK...Ive never seen someone add the digital as you have Rich. And youve experienced the same symptoms? You got the skinny on this one for sure. Could we get Rodney to post up the thermostat make and do some follow up? I think Ive seen these symptoms once with a standard thermostat. It would be nice to get some closure on this one...

[Rodney Behrens]

Thanks for all the info, I won't be able to trouble shoot till this week end. The cycle time was probable more than 5 secs. we only had the furnace running at night. '84 is kinda old right? Ha. I'm sure it's the original thermostat, and it has electronic ignition. I'll let you know what I find. Thanks again. Rodney. 

[Rich Thomas]

84 isn't as old as you think. Mine is a 78 But, it works great now. by the way there's a lot of info on here about furnace repairs and a lot of people to help you out. David is one of those "go to guys" that have been there and done that. if you need parts there are links to sites that provide parts and classifieds for almost anything you might need for your older camper. good luck with your troubleshooting.   

[david craft]

another possibility.  you should get a couple degrees F separation on the thermostat, if the little magnets are lined up right.  Id try the trouble shoot mentioned earlier and do the thermostat if the time delay works out.

[Rodney Behrens]

Well I fired up the furnace last night and after calling for heat 3 or 4 times the fan cycling problem only happened once, the fan would come on for approx 1 sec. then off approx 2 secs. this morning pulled the furnace out and removed the fan switch and did a bench test on it with a heat source.it seamed to work ok, n.o. when cool and closed when hot. One thing I noticed is there was continuity across the switch a moment before it clicked. By looking at the wiring diagram the only way the fan gets power is from the fan switch or the thermostat relay, correct? I installed the furnace and ran it a couple of times with out the thermostat and the fan cycling happened again, on for approx 1 sec. and off approx 2 secs. for about 5 cycles and then off for good, after I heard the fan switch open. Bad fan switch? 

[Rodney Behrens]

Just to clarify, I heard the fan switch open before the fan cycling and didn't hear it again.