Small dometic furnance

KevinK · 09-16-2022, 03:20 PM

Have the micro Minnie 1708fb, furnance will not ignite after three uses. Blower runs for 20 sec then stops . Any ideas ? Other gas appliances working

**creativepart** · 09-16-2022, 03:29 PM

This indicates that it’s not igniting the gas or not sensing the ignition. It can be a fairly large number of things that cause this. Unless you want to get deep into trouble shooting perhaps a knowledgeable tech would be the best.

This assumes you are sure your LP tanks have gas in them and are turned on. I assume this is so because of your statement about of appliances.

When my furnace did this it was a faulty circuit board. But honestly there are 3 or 4 other things that could cause this.

Morich · 09-16-2022, 04:39 PM

Several ways to go on this and oneis to look for some semi-obvious items first.

One big thing is to know what to expect.The "normal" operation for manyfurnaces is the same as follows.
1. The blower comes on, that starts air flow through to move air inside but also move the combustions products out! So they put a small item called a "sail switch" in the airflow. As the "sail" moves it closes a switch to let the rest of the process follow.

2. The sail switch says there is good airflow lets the board then opens the gas valve, gas flows and an igniter lights the gas. The fire burns until the thermostat inside says it is warmed to what you have set.

We can often see and follow each step if we know what to look for at the time. We can say your thermostat is calling for heat, so okay. Where things fall apart is the airflow sensing and that is a very common item to fail due to a couple things.

One of the big things is whether you have screens over the vents on the furnace, water heater and frig! Those little holes look like a welcome sign to things like spiders, wasps and mud daubers, so if they are open there is a pretty good chance they may have moved in and built a nest in the vent so that airflow is restricted!

A wire like a coat hanger stuck in and flopped all around may snag a nest out. A leaf vac or blower can be a handy item to clear the debris once knocked loose.

Approach with care if it's still nesting weather in your area as they do take offence at that move!

It could be other things but that would be my bet as it will try several times to get airflow and then quit until reset.

Once you get good air, there should be a click and if you are resting a hand on the gas valve, you can feel it move. If not familiar with gas valves, it will be a large "bump" in the gas line with a couple wires going to it!
Get the air flow, gas valve opens, then you should also see or hear sparks or clicking from an ignitor or sometimes it will be a form of glow plug which heats red hot to light the gas.

But if you've gotten this far, be aware that there may be something blocking the tube which carries the gas from the valve to the place where it ignites and that tube can be blocked the same as the vents.
The trick is to stand close enough to watch what is happening but not so close that a bunch of gas gets into the tube but can't get to the igniter! If a bunch of gas builds up, back off to let it clear so not to be involved if it lights with a swoose!

See if that gets you started and report what you find. No need to blow your mind on too many things if you find it on first thought! Could be bad/ corroded connections or bad board but no need to jump there just yet?

KevinK · 09-16-2022, 05:16 PM

Thank you so much … will look at it . I have a very small dometic , I believe it only pulls out from inside . Do They simple slide out after removing screws ? A long gas line and long electrical cable ?

Morich · 09-16-2022, 05:57 PM

Lots of different types, sizes, styles so one of the better ways to get definite info on which exact one you have is to look on the furnace for a label that gives the model number.
Then with that info do a search for manuals on that modela. If nothing else, the manuals will often show diagramsof how it all fits and connect together.

But there is also a good chance that a good search of the model number will show up a troubleshooting flow chart. That flow chart may give a step by step procedure to follow, just as I described-----only lots more detailed and much more likely to exactly right for the one furnace you have.

My general ideas of what most common types do can miss some of the small details! They often even have a picture of the parts instead of me telling you what I think it looks like!!

Any chance you got a small booklet for the furnace? They do a good job of forwarding info on motorhomes but trailers get far less attention.

JoshBap · 09-21-2022, 05:01 PM

Read up on “sail switches”. I had the same problem with mine and that’s what it was. Cheap part on Amazon. Kinda hard to believe the way it’s engineered. The access to my 2019 mini is under the fridge. You have to take the electrical panel off, the vent next to it, and a panel. It’s a pain in the butt to remove but not worth paying a shop or waiting for the repair time if ur handy at all. It’s also a good way to learn to repair it in case u need to in the field. I now carry a spare sail switch with me in case I’m somewhere and need my furnace, if it goes out. I believe I posted a thread on here with pics on how I did it, but I don’t know how to link it to this post.
Hope this helps

KevinK · 09-21-2022, 05:29 PM

Was yours obviously broken or just dirty?

KevinK · 09-21-2022, 05:29 PM

Quote:

Originally Posted by JoshBap

Read up on “sail switches”. I had the same problem with mine and that’s what it was. Cheap part on Amazon. Kinda hard to believe the way it’s engineered. The access to my 2019 mini is under the fridge. You have to take the electrical panel off, the vent next to it, and a panel. It’s a pain in the butt to remove but not worth paying a shop or waiting for the repair time if ur handy at all. It’s also a good way to learn to repair it in case u need to in the field. I now carry a spare sail switch with me in case I’m somewhere and need my furnace, if it goes out. I believe I posted a thread on here with pics on how I did it, but I don’t know how to link it to this post.
Hope this helps

Was yours broken or dirty ?

Morich · 09-21-2022, 05:44 PM

Does this look like the post you mention?

https://www.winnieowners.com/forums/...ds-363351.html

Adding the link can be somewhat simple----I "think" as I'm no computer guy!

I found the post, got it onscreen, highlighted the address, copied it by hitting "CTRL and C", came back to this post where I wanted to reply and hit "CTRL and V" to add it where wanted?

But is that the post you wanted???

On the point of having or finding the sailswitch, there can be times when we can work around that issue of having to get an exact match for what we have.

The sail is an item that would be hard to replace but it is also not too likely to wear out or break, so the part we need to replace will often be just the microswitch that the sail is attached to and that is a very common item.
So before we get to far into looking for an RV specific item, it can pay to look at what it might take to swap the sail off the defective micro switch and add it to a new one.

If you see a way to swap the sail over, the specs on the switch are very common. Just look for a switch that will carry 12Volts or more and the current is pretty low, so not often a problem. Rated for 125 Volts is fine, just not less than 12?
The last and most important point on shopping the switch is to make sure the contacts on the new will match the old as far as being NO (normally open) or NC (normally closed) and that part may be easy as lots of these small switches come with three lugs to let you decide if you want NO or NC, just use a different lug.

The difference in price is pretty dramatic but the bigger issue can be the ease of finding the common versus getting an RV specific item!

Check the difference here!

sshephard · 09-21-2022, 05:56 PM

I’ve had to pull my furnace twice due to a faulty sail switch. The second time I decided to document it. As others have said there are other things that can be wrong so my experience and documentation may not help. Nevertheless, here’s the link

https://scottshephardphotography.com/winnebago-2018ds-furnace-removal

JoshBap · 09-21-2022, 06:01 PM

Quote:

Originally Posted by KevinK

Was yours broken or dirty ?

Well, when I first opened it, it was super dirty. A hair ball was around it. So I cleaned it, and it started working when I tested. Put it all back together……stopped working again. So, bought the part and had to take it ALL apart and swap it out. No problems since. It’s a very poor design as it’s just really a dirt and hair catcher in there.

KevinK · 09-21-2022, 06:03 PM

Thank u so much - I will check the limit switch, and sail switch and hope it’s not a board . Is dometic good with providing parts if under warranty ??

KevinK · 09-21-2022, 06:05 PM

Thank u

JoshBap · 09-21-2022, 06:07 PM

@Morich thanks!!! That IS the thread! I am also not good with computers. I’m hands on and had read about sail switches going bad. So, in order to know the exact part to order for my furnace, I took it all apart. Took pics of everything and ordered it. @Kevin not sure if they’re good at furnishing parts under Warrantee but because the part is relatively cheap and wait times can take forever, I just went ahead and ordered. Once I knew it was working and solved my issue…I went ahead and ordered another as backup.

Dave V. · 09-21-2022, 07:20 PM

Hi Kevin! Anytime I’ve had issues with my furnace it’s either a sail switch or a motherboard.
Sail switches are easy to obtain and in a lot of instances easy to replace.
Motherboards more an issue but can be replaced with a little ingenuity.
Check Amazon for pricing.
Hope this helps.
Dave V.
2022 2701RBS

R1campr · 11-05-2022, 08:16 PM

Thank you so much for this article, Sshepard. I’ve been searching for how to do this for a while.
One question, is that sail switch kit the part number 33081?

Morich · 11-06-2022, 07:19 AM

If you have the sail swicth out and can look at it a test may be in order? It is just a microswitch, so test if power can run in from one lug to the other when closed (continuity?)and then see that it opens?

But while looking at it, one can sometimes see a better way to replace it if needed? Avoid RV specific parts when possible!

Depends on build and not a sure thing but if the sail part is just something you can get off the old switch, and on a new, look at going to a local electronics place for just the switch!
Lots of nearby places to avoid shipping and waiting!

R1campr · 11-13-2022, 09:38 AM

I was able to get the furnace out. Looked like the builders installed the furnace before the refrigerator, and the wires for the fridge were tangled with the furnace wires. Once I got them untangled, it was pretty easy to get the furnace out.
I tested the sail switch by holding it down and the spark ignitor works, and no flashing light on the board. No dirt, hair, or anything on the sail switch. I reinstalled the switch, tested with the thermostat again, no spark, and the light is flashing on the board. I’m assuming the actual switch works, but it seems the sail isn’t pushing the switch enough to close the circuit, or something is hanging up the sail.
I heard on a Facebook page to try and bend the sail a little closer to the squirrel cage, I’m gonna try that first before I replace the sail switch kit. The kit is #33081, for the small furnace. I am going to compare the 2 switches and brackets. If there’s any difference from the oem and new design, I’ll replace it even if the oem one works after bending the sail and testing it again.

Morich · 11-14-2022, 07:24 AM

Little micro switches only have to move the small point just a little and that can be fussy. Sometimes we can see how bending justy a little will make it work,but it's a careful deal.
Fine line between not pressing enough and too much.

Good luck! It's a tough one when the furnace is hard to get at. That is one that I've not fought as the back of the furnace is sticking out on the RV I've had.

R1campr · 11-18-2022, 06:52 AM

So, I took the oem sail switch out and bent the sail slightly, put it back in and it works like it’s supposed to. Since I bought a new (improved?) sail switch kit, I replaced it anyways. When I had them both out, I compared them and didn’t see any difference in the switch or the mounting bracket. I put the new one in and it doesn’t work. So I took it out, tested it, and it works by pressing the sail down. I tried bending the new sail like I did the oem one and still wouldn’t work when in the furnace. So I installed to old one back in the furnace and it works as it should.

This sail switch 33081 is more expensive than the 33082. The switches look the same on Amazon and the brackets are obviously different. Anyone know if the sail switches themselves are interchangeable? Was thinking if they are, I’d get a cheaper one to keep for a spare and returning the 33081 kit that won’t work in my furnace.