Furnace issue

[Ronfire]

I have an Atwood 4920 furnace in my Living quarters horse trailer. I have been having an issue with the furnace. It will ignite and run fine, then when it runs for 10-15 minutes shuts off. Mostly it just quits but sometime it will have the fan stutter and then quit without the cool down cycle I have replaced the main board, reset breaker switch and temp cutout sensor.

The thermostat is turned up enough, batteries are new and well charged and the fan runs well and lots of propane on a 100lb tank. All the other gas and electrical items work well.
The red indicator light will flash steady after it cools down a bit with the thermostat still set on and the switch on the furnace reset. I can not find a reference to the steady slow flashing of the indicator light.

I think my next move will be to pull out the furnace and bench test it when I get home. The fan motor and sail switch are hard to access when in the trailer. I suspect the problem might be in this area but the fan sounds like it is running strong.

At this time it is not a pressing repair until I return home as it is only cool in the mornings and the furnace will bring up the heat for awhile then shut off. I have a Dickenson marine bulkhead heater as well and that will help keep it warm until I find he issue.

 

[jsb5717]

I assume that your furnace is shutting off before the desired temp is reached? The thermostat is set higher but the temp doesn't get there before the furnace quits?

You know that the sail switch is fine since the unit fires up and runs. The fact that it runs fine for ~15 min tells me that all of the functions are working. So the issue is why does it shut off prematurely? Do you have a resettable fuse for the furnace? Check in your fuse box to see if the fuse is black or blue. The black one is resettable and glitchy. Replace it with a standard blue 15amp fuse. Other than that, in my mind the issue sounds like it could be a faulty main control board or thermostat.

You could test the thermostat by jumping the 2 blue wires, bypassing the thermostat. The furnace should turn on right away and continue to run until you un-jump the wires. That might tell you something.

 

[NH_Bulldog]

My thought is that it is shutting off on high-limit due to insufficient airflow through the unit, or restricted heat duct/registers.

 

[Ronfire]

Furnace

The fuse is a standard type fuse. If it was a thermostat issue the furnace should go into a cool down before shutting off. This issue shuts of the flame and fan at the same time. I have replaced the board, reset beaker and temp sensor when it first started the issue. I have blown out the furnace from inside and out so there is no blockage in the system and I have not changed any of the outlets for the furnace. It vents with ducts and direct out the front. I might try and bypass the high temp sensor and see if that solves the problem. It almost looks like the burner is putting out to much heat but the burner has been replaced, not sure if the issue started right after that.
The burner is the correct one for the furnace. Wonder if the jet could have worn larger and is getting to much propane.

 

[chuckster57]

My thought is that it is shutting off on high-limit due to insufficient airflow through the unit, or restricted heat duct/registers.

That would be my thought.

OP: you need to test it while it’s installed in the trailer. I use long leads and an Ohm meter set to continuity.

 

[Ronfire]

Tests

I was thinking of connecting an ohm meter in parallel in the temp cutout sensor to see if that is causing the shut down also could use my laser temp gauge to get an idea if it is to hot.

 

[Quinla]

You’re probably right about the fan motor or sail switch. If airflow drops, it could trip the shutdown. Bench testing sounds like a good plan, and the Dickenson heater should hold you over for now.

 

[chuckster57]

I was thinking of connecting an ohm meter in parallel in the temp cutout sensor to see if that is causing the shut down also could use my laser temp gauge to get an idea if it is to hot.

You’ll want the furnace “in place” with all covers and ducting in place, that’s why I run test wires and a meter. Bench testing works most of the time, but I have a suburban furnace that runs all day long on the bench, but won’t work in the trailer. I have even monitored gas pressure while operating.