Furnace not working - No blower, ac fan comes on, no red error light on the board....

[GetDunn]

I have a 2018 Montana 2131rl 5th wheel. When turning the thermostat to heat mode and temp set higher than the room, I hear nothing except the fan from the AC turns on and no blower from the furnace. Also, there is no error code from the red light on the control board. However, I read 12v power at the board on the red wire on the blade next to the blower motor power. The blower motor works when jumper is applied.
We have rarely used the furnace since buying it used in 2020, but it did work at the times we tried it in the past. I am usually a DIY guy. But this is a head scratcher for me. Any thoughts? Thanks

 

[jsb5717]

Make sure your fan is set to "Auto". That will keep the AC fan from blowing when the Tstat is calling for heat.

What kind of thermostat do you have? If it's the InCommand system I won't be any help but I know that those can be glitchy. There is a relay in the AC that directs the signal to the furnace that can go bad. The control board can also go bad. Have you checked the fuse for the furnace? Make sure to use the standard blue 15A fuse, not a black one. The black ones are resettable and are glitchy.

The very first thing that should happen when the thermostat is set for heat is for the fan to spin up. So if that's not happening then it's likely not the furnace (unless you have a bad control board). But all other processes occur after the fan spins up so those aren't worth checking at this point. IMHO it's time to start tracing power and signal to the furnace. Fuse, Thermostat, AC relay, etc.

 

[Daryles]

Hope this helps

 

[GetDunn]

Make sure your fan is set to "Auto". That will keep the AC fan from blowing when the Tstat is calling for heat.

What kind of thermostat do you have? If it's the InCommand system I won't be any help but I know that those can be glitchy. There is a relay in the AC that directs the signal to the furnace that can go bad. The control board can also go bad. Have you checked the fuse for the furnace? Make sure to use the standard blue 15A fuse, not a black one. The black ones are resettable and are glitchy.

The very first thing that should happen when the thermostat is set for heat is for the fan to spin up. So if that's not happening then it's likely not the furnace (unlethe ss you have a bad control board). But all other processes occur after the fan spins up so those aren't worth checking at this point. IMHO it's time to start tracing power and signal to the furnace. Fuse, Thermostat, AC relay, etc.

Thermostat is the Dometic single zone/3 wire/ black. The fuse is good. I did the swap out for that black 15a fuse. Thanks for the answers. Still working on it.

 

[jsb5717]

Random thought: Do you have a heat pump? When you set the thermostat for heat are you sure you are set for furnace heat and not heat pump heat? If it's set for heat pump then you will hear the AC fan since the heat pump is the AC unit running in reverse. The heat pump is useful down to about 40 degrees.

 

[whited Haired Pa Pa G]

Random thought: Do you have a heat pump? When you set the thermostat for heat are you sure you are set for furnace heat and not heat pump heat? If it's set for heat pump then you will hear the AC fan since the heat pump is the AC unit running in reverse. The heat pump is useful down to about 40 degrees.

Can I just turn on the furnace without having to go through the heat pump at any temperature?

 

[jsb5717]

Can I just turn on the furnace without having to go through the heat pump at any temperature?

Sure...you should be able to select which "Mode" you want on your thermostat.

 

[MJohnston]

I have the same year and model as you. It does sound like you are turning on the heat pump and not the furnace. The furnace will be the next option on the thermostat controller.

I have had issues with the sail switch when using the furnace in colder weather, but that fails after initial fan spin up and you can see the blinking red light when you take off the cover. I have had to remove and reinstall the sail switch a few times during the winter (usually in the middle of the night). So now I keep a spare handy.
I hope you figure it out!
Michael