Furnace Ignition Switch? 2021 Micro Minnie 2108TB

[Lilojo73]

We have a new-to-us 2021 Micro Minnie 2108TB and are trying to learn how all the systems work. We're trying to figure out how the furnace works (Dometic). If I put it on heat, with auto fan, air blows out of the ceiling a/c vents, and you can hear the a/c unit on top working. No heat is coming out of the vents along the floor. The generic manual that came with the trailer instructs you to "turn the ignition switch on" that is located on the exterior power panel. We can't find an exterior power panel. We had the propane on, and the batteries are fully charged. I read about a "sail switch" for the furnace, but the only sail switch I found was the battery one located in the storage hold. Any ideas of what we are doing wrong? Thanks!

 

[Fred 2106DS]

Something doesn’t sound right. If you select furnace and have the fan set to auto (Au) the fan for the A/C shouldn’t come on. As for “turn the ignition switch on”, I don’t believe that is pertinent to your camper. As for the sail switch, that is inside your furnace. Below are a couple videos you may want to watch. The first one deals with Dometic Single Zone Thermostat and the other two will show you how to troubleshoot an RV furnace. The second furnace video gets into hands on troubleshooting and what to listen for.

How To Operate A Dometic Single Zone (SZ1) RV Thermostat

RV Furnace Troubleshooting - An In-Depth Look At How To Do It -- (Part 1) -- My RV Works

RV Furnace Troubleshooting -- An In-Depth Look At How To Do It -- (Part 2) -- My RV Works

 

[Morich]

I might share a slightly different way to go as I am sometimes disappointed in how much time I have to watch videos and then find out it was not actually correct on the fine points for my furnace as it was a different model.
Electronics and things like furnaces and thermostats change just as quick as cell phones and we do need to get the right info to pick up the right small points.
So I look at the item like the furnace or thermostat and search for brand and model info on that item .
Info from ten years ago is not likely to have good info on what is in your 2021 RV!

But a common item on many furnaces is the sail switch and it can be confusing.
Called a sail because it hangs down in the airflow that is used by the furnace to move combustion air for the flames in the vent and out the exhaust of the furnace.
You likely have two round holes on the outside wall near the furnace?
Cold air goes in one and comes out hot from the other! Inside the furnace there is a section where the fire is kept separate from the inside RV air which is drawn into the furnace, heated and comes back inside!
Like your home furnace, the fumes are not pushed into the house but go up and out the vent!
But there is a major difference in RV furnaces as a safety item.

In an RV, we don't open the gas valve and let the RV fill with propane if the furnace fails to light!
On RV furnaces the blower comes on before the gas flow starts. The sail switch "sail " hangs down into the combustion airflow and if that sail doesn't get enough air movement to make it close a microswitch, the gas valve doesn't open!
Normally the small Dometic types will try three times to get it right and if not, they go into lockout and shut down until the problem with the sail switch is cleared!
Not filling the RV with propane and then letting it light is a good thing! So the sail switch has to sail first!
Different brand but same idea!

But that doesn't seem to be the problem as you are not getting the right blower to come on when calling for heat. for some reason you are getting the air conditioner blower to come on first, so I suspect a thermostat or wiring problem!
Basic point is putting warm air down low as it will rise but cool air comes in up high and sinks!
Air should come in lower vents for a bit and THEN hear the fire light and begin to warm the air coming in!

 

[Wmlunt-WO]

Lilojo73, you likely have the same setup as my 2024 MM2108.
The fan setting when in heat mode just turns on the upper a/c fan, and is independent of the furnace system. It can be used to circulate the air in the RV if you get layers of cold and hot air, I leave it off.
When in heat mode, turn the temperature setting up way higher than it is in the room.
You should feel air blowing out of the heater vent ( mine is below refer) almost immediately. Then you can hear the furnace light and the air will get warmer. (Make sure propane is full and turned on, light stove burner to ensure there is gas available)
If you don’t get the airflow from the furnace vent, there is something wrong, and see trouble shooting above.
If it shuts down and burner not lighting, likely sail switch as described above. It may have gone into lockout before you got the trailer.
Btw, I would make sure you have lights on your co detector, and leave windows open during testing. If you spray unburned butane into co detector it should chirp…
The burner ignition is automatic requires nothing you need to do.
Bill

 

[Morich]

Each year and brand or model of furnace will have it's own specific points that make it different. That makes it important to get the correct info as small points as mentioned will be different on each unit.
The air circulation item is not one I have found before.
Mu suggestion would be to look on the furnace for the brand and model number if no info is on hand. Then when armed with the basic stuff, you can go online, input that brand/model info and search for the correct manuals. You will often find some which are only operation manuals to tell how to work the furnace or you may want to go further and have a more complete manual that has all the troubleshooting info included.

I assume trouble will come up at some point when I get a different RV and one way to cut the drama when it does come up is having a stack of written info on each item!

And that gets around to an item that is a frequent problem on RV furnace. In most parts of the country there will be a number of different insects that love to build nests in small spaces. Things like mud dauber and paper wasps of different types?

They seem to love the smell of propane and those furnace and frig vents look like home to them~!
When they go in and find a handy little thing sticking out of the ceiling, they love to build a nest.
That handy thing is often the sail switch and they build a nest that stops it from moving!

Then the furnace will start blowing but the sail switch doesn't close to tell the system there is safe airflow, so it never opens the gas valve and lights! Depending on model, the furnace may try three times and then lockout! At that point, you have to figure out how to reset the lockout as well as clear the nest off the sail switch. Bummer and lots of wasted trip time?

I find it much better to assume they will find my RV at some point. I find some form of vent screen to put on the frig and furnace vents as much easier to do it when I am home and have time.
Doing repair, under stress on the road side is something I work to head off!

You can buy ready made kits or fashion your own. I do my own as it may be difficult to find the right exact shape in ready made. Each brand/model furnace or frig may have different shaped vents!

One point to keep in mind is not using window screen as it can get dirty and block too much air flow. I find something too small for a wasp but big enough to let air pass!

It's a trek but live, learn and adapt as needed!

 

[Lilojo73]

We ended up taking the trailer into the local Winnebago dealer. They found a crimp in the propane line. No problems since they fixed it. Thanks for all the advice!

 

[Wmlunt-WO]

You bet, thanks for getting back to us!
Where was the kink?
Under the cabinet by sink?
Bill

 

[Morich]

I've heard of some weird stuff but the idea that a crimped gas line makes a different blower come on is a bit of a stretch!
The way a normal furnace should work is the furnace blower should come on as a first step. Then if the sail switch finds there is good airflow, the timing moves on to allow the gas valve to open.
The normal furnace would find there was no gas and never light!
At that point it does the retry and goes into lockout!
It would be really interesting to hear them explain how a crimped gas line makes the blower on the air conditioner come on!
Something wrong with this whole story!

But congrats on getting it fixed as that is the primary issue!

 

[Lilojo73]

It was behind the stovetop.

You bet, thanks for getting back to us!
Where was the kink?
Under the cabinet by sink?
Bill

 

[Wmlunt-WO]

Morich, you don’t understand the system here at all.
The furnace is its own system with burner and blower to produce hot air, controlled by the thermostat.
The thermostat has 3 modes, fan, heat, and air conditioning. The fan is the air conditioning recirc fan. If you leave it on in the heat mode, the furnace runs and blows the heated air thru the box on the floor, recirculating hot air.
But also runs the a/c fan if it is set to low/high/auto. I suppose this is to move air around the trailer rather than have a single point of hot air entering the trailer.
Typically this fan would be set to off in the heat mode.
Bill

 

[Wmlunt-WO]

It was behind the stovetop.

Ahhh, thanks for the update. Too many pots in the drawer below? Or just a WBGO error you think?
Bill

 

[Morich]

Quick question?
How does a mashed propane line keep an RV furnace blower from coming on?
What effect does the air conditioner blower running have on the sail switch?

 

[Wmlunt-WO]

No propane would not allow it to light, hence shut the furnace blower fan off. 3 try’s then lockout.
None, the a/c blower fan is a separate system from the furnace. In heat mode the t’stat turns the furnace on and off , controlling to the set point.
The t’stat has no control over the furnace blower, the furnace controls that blower, on to light and when burning, off when furnace is off.

The a/c blower is on the fan setting of the t’stat when in heat mode.

While in heat, air conditioning, or fan, the fan setting on the t’stat runs the a/c blower in low, high, auto low, auto high, or off. Can’t explain it any simpler than that. 2 separate systems.

 

[Morich]

Quote:
The t’stat has no control over the furnace blower, the furnace controls that blower, on to light and when burning, off when furnace is off.

Is this actually what you meant to say? A bit like saying the ignition key has nothing to do with a car engine starting! The engine just starts because it feels the need?

At this point there is no more to discuss!

 

[Wmlunt-WO]

The furnace blower is local to the furnace. The t’stat turns the furnace system on and off, it can not run the furnace blower (fan) independently.
The fan shown on the t’stat in heat mode is the a/c (fan) blower.
A/c blower comes out the roof vents, heat blower comes out the heat vents near the floor.
An owner may think that when in heat mode changing the fan setting shown on the t’stat would change the heat blower fan speed, but that is not true.
For future owner reference.

 

[Wmlunt-WO]