Furnace Shutting Down - New Legacy 3121rl

[USA-C2C]

Sold our Airstream and bought a Montana Legacy 3121rl. New to 5th wheeling. Just took delivery after waiting for parts and dealer to fix bedroom slide (another day, another story).

Although I am plugged into 50 amp source at home, I set the HVAC IN-Command setting on rear A/C and chose Heat mode with gas source and fan off. I believe the furnace only runs off gas but the heat pump on the AC runs of electric.

The RV was cold, probably around 50 degrees, so I thought I was setting the thermostat to call for heat until the temp reached about 87 degrees (wanted it high to warm it up and test the furnace). See picture

The furnace engaged and started heating but after about 10 minutes it stopped. No other fan, or vent was running and the fireplace was also off.

I reset the rear AC to off, waited a minute or two, and then set it again to heat mode, gas, fan off and the furnace engaged again and starting hearting but then stopped again after about 10 minutes. Repeated the same procedure a third time and again the same results.

Not sure if I am doing something wrong or if I have a furnace problem. Any ideas are welcome. Obviously, I am testing many things and I have a list for the dealer.

[M&M]

First thing I’d recommend checking is the black relay in the dc fuse box. Many post on it resetting. When unit goes off, if it’s the relay, a red light will be on beside it. Work around is replace with standard 15amp.

Your setting for furnace only is correct. Fan Off will only run furnace.

[Hooterville]

For gas furnace operation your fan must be set to "auto"

[USA-C2C]

Thanks and if the dealer doesn't get it right when I take it back, I will let him know your comment about replacing the black relay with a standard 15 amp

[mccleskeb]

We have a 2022 Legacy 3121RL too. I was having a similar problem with our furnace. The only difference is ours would turn off after about a minute or so. We took the rig to the dealer to work off some "punch list" items. Turned out to be a fuse that is located near the furnace . . . not in the dc fuse box. They said you have to remove the external furnace cover to access the fuse. Might want to check it just in case you are having a similar problem.


Bob & Kathy
2022 Legacy 3121LR
2019 RAM 2500 gas long bed

[Cheese]

Do you no what the red lighted switch is for below the in command center on a 3121 legacy ?

[USA-C2C]

I could not see a red lighted switch on my unit - can you send a picture?

[Kyle and Lisa]

Check your furnace exhaust tube after removing the cover for dirt dobber nest with a flashlight, that is usually the issue, restricted air flow.

[RipNC]

Misread post.

[RipNC]

If not the reset fuse or the fan setting as others mentioned, check that your propane valve(s) are fully open so it isn't starved for fuel. Otherwise it sounds like a limit switch (temp or air flow).

[USA-C2C]

Thanks and good point - I did check the propane values and the were open. Dealer have the RV and is trying to troubleshoot the problem now. I gave them these montanaowner's comments.

[Cbrandt79]

We have a 2021 legacy 3121 and experienced this exact problem for quite a long time. I replaced the black 15 amp fuse and problem solved. Keystone did a lot of part replacement as we we are full time. Good luck!

[snowmanfx4]

If you are going to use the heat pump and not the furnace. If it is 50 degrees in your camper. You can only have the heat pump at 54 degrees. If you set it 5 degrees or more higher the furnace will come on too. Your heat pump will not heat if it is much lower than 50 or less. Some times the furnace will help to warm up the camper then shut down. After the camper temp comes up you can turn it as it warms up. Just not over 5 degrees at a time.

[Fred]

What was the outside temperature? The Heat pump is almost useless as soon as the temp gets into the 40s or below.