furnace problem

[NEWYORKHILLBILLY]

I been on a 6 week trip and am having furnace problems. what's happing is the burner keeps cycling, tried 3 sail switch's and ruled out that, it will light as normal and sometimes run 2-3 hours into the night. Then the sail switch will break contact for a 1/2 second. burner will shut off then relight 30 seconds later and keeps cycling like that on and off until I shut it down. it does not lock out. hoever for teh 1/2 the sail switch breaks contact the red light on the board will flash. DC voltage to the board is 12.5 volts. but if you plug it into AC 13.35 volts it will run fine. I think the extra volt is increasing fan speed enough to compensate for another issue I am thinking i must have air obstruction or bad motor. I read all the prior threads looking for help. Can you remove this fan cover to clean things out without removing the furnace? my model is Dometic DFSAD12131 need to get fixed 20-degree weather coming,

[ChuckBC]

I had similar problem with cycling and it would keep trying to ignite even more than the 3 attempts with shutdown. I think I have solved by slightly bending sail switch paddle possibly helping with a steady blower airflow holding open. The other change I made was adding a bathroom vent. This does allow more blower airflow which others noted as a possible cause for furnace problem. Mine appeared fine with single large duct but added vent may have helped? I used furnace this last month and ran properly.

[TZBrown]

Air flow restriction may cause part of your problem

Check out this post and see if it may benefit you
https://www.escapeforum.org/forums/f...tml#post273150

Simply removing the outlet grill is a test of the volume of the airflow.
slightly low voltage will affect fan speed and also cause the sail switch to drop out.

There are other posts in that same thread that may help with your diagnosis

[Carmel Clown]

This last trip our furnace continued to blow air after I turned it off. I finally set the temp real low and it stopped. Haven’t had that problem before. Ideas?

[MVA]

Originally Posted by Carmel Clown

This last trip our furnace continued to blow air after I turned it off. I finally set the temp real low and it stopped. Haven’t had that problem before. Ideas?

How long did it blow air? The blower continues to function until the internal furnace temperature is lowered.

[Carmel Clown]

Can’t say. Odd thing is, it cycled off, then back on. I haven’t tested it since we got home but I will.

[MVA]

If it cycled back on once for only a few minutes, I would not be concerned. I suspect the control circuit in the furnace is similar to a residential furnace in that the air circulation blower stays on until the internal temperature is below a set value. When the blower turns off, heat in the internal components could reheat the air in the furnace causing the blower to turn back on for a few minutes. I believe I have seen this effect in our trailer.

[Iowa Dave]

Both of the furnaces we have had (19&21) would double cycle especially when we come into a cold camper, turn the furnace on to a fairly high temp setting and let it run. We may just step in for a minute to turn it in and go back outside to buckle up for the night or watch the campfire longer. The furnace makes temp after running a while and one of two things happens. Either then heat in the unit needs cooling off via the fan or disturbance of the warmed air inside cools the trailer enough to make it come on for a short time again when we go inside for the night. I wouldn’t worry about “double cycling” especially if it’s run for a while. It gets pretty hot in the unit and takes some time and fan air to cool it off. Once inside and settled in for the night ours have both cycled normally and predictably depending on steady or declining outside temperatures.
That's my experience
Iowa Dave