Furnace - propane stop/start during its on cycle?

[groundhogy]

Yes the furnace will come on.
Then sounds like the flame goes out, and then lights back up, all during the on cycle. Fan continues to run. Furnace completed its cycle ok.
Pending doom? Lol

Its a Dometic AFMD30141
May also have an Atwood number. Maybe 32684.

[dougrainer]

"Regulator malfunction can result in higher propane pressure to the furnace which affects flame size.. Check the burners on your stove, flame should not be excessively high and should be all blue".

This will not work. The Stoves/Ovens have their own regulator set at 10 inches water column. So if the LP regulator is too high this regulator will fix that for the Oven/Stove. Doug

[dougrainer]

How long between flame on and off? YES, it is normal for a LOT of RV's. Because the OEM did NOT install the ducting to Furnace install specs. This causes the Hi Limit switch to kick in and out during the cycle. The furnace overheats due to the lack of adequate ducting to remove the heat from the burner chamber. So, as other have suggested, an RV furnace it is NOT a good idea to clock off some duct covers to get more heat to another area. Even blocking just one duct cover will cause this. Most common cause is the round 4 inch flexible duct hose in kinked or smashed somewhere inside the floor or cabinets, if the ducting is installed to furnace specs. Doug

[Gdetrailer]

Get the battery charging, low battery voltage for sure can cause the furnace fan to not run fast enough to keep the sail switch on continually (one of the safeties) causing burner to turn on/off intermittently..

[groundhogy]

Lol..
You guys may be geniuses.

I am not at RV at the moment, but both of your ideas may be correct.

I have a 6 yr old that keeps tossing her blanket down near the back vent.
I keep yelling and picking it up.

Last night I got home to.. no batteries being charged.
(I will post on this too.. GFI breaker in breaker box)

So I turned everything 12v off except furnace last night so furnace would last the night.

[wildtoad]

Make sure output vents are not closed off, make sure return is not blocked or if someone installed a filter thinking it’s like a home furnace.

[Gdetrailer]

JimK-NY wrote:
This topic has come up several times in the past. Some responses have recommended checking the ductwork to be sure there are no restrictions.

I am of the opinion that this is normal operation for some RVs and for some furnaces. My burner definitely cycles on and off numerous times when raising the RV temperature by several degrees. This has always been the case and my rig is almost 20 years old. I have never timed the cycles but I think the burner probably runs for 3 or 4 minutes and then blows air for almost that same period of time before the burner starts again.

I am not sure I would call short burner cycle "normal", none of the RVs I have had have done that.. My current TT I have taken the temp from 40F to 70F and never once had the burner turn off.

Perhaps normal for yours if the RV manufacturer did not follow the furnace manufacturers minimum ducting requirements which would not be unusual..

Furnace manufacturers do list cold air return minimum opening and also minimum hot air outlet requirements in square inches for each BTU size of furnace.. Wouldn't surprise me if the RV manufacturer failed to follow or exceed the minimums..

[2oldman]

I assume the propane supply is adequate..?

[JimK-NY]

This topic has come up several times in the past. Some responses have recommended checking the ductwork to be sure there are no restrictions.

I am of the opinion that this is normal operation for some RVs and for some furnaces. My burner definitely cycles on and off numerous times when raising the RV temperature by several degrees. This has always been the case and my rig is almost 20 years old. I have never timed the cycles but I think the burner probably runs for 3 or 4 minutes and then blows air for almost that same period of time before the burner starts again.

[Gdetrailer]

Burner short cycle..

Ductwork air blockage..

Did you shut or block off any ductwork registers? Blockages or intentionally closed off vents slows the air flow going across the heat exchanger, this increases the temperature until the over temp safety trips the burner off until the temperature drops to a safe level.

Fan running too slow..

Check your battery voltage at the battery and at the furnace. Since the fan motor is DC it runs directly from your battery and when the battery voltage sags, so does the motor speed and the reduces the air flow causing high temperature safety to trip and turn off the burner.

Too much propane pressure..

Regulator malfunction can result in higher propane pressure to the furnace which affects flame size.. Check the burners on your stove, flame should not be excessively high and should be all blue.