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Old 02-10-2021, 11:37 AM   #1
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Atwood Furnace Not Working, Again

So, I thought I had fixed my Atwood furnace but it decided it wanted more of my attention. See: https://www.airforums.com/forums/f44...ve-218096.html

Went to turn it up a little for the coming, now here, cold front. Same problem as before.

It starts the exhaust air cycle but never activates the gas solenoid or start the piezo igniter. There's plenty of gas, stove next to and down line works fine, all 3 burners, proper color and size of flame.

It's time to double check the connectors. I did a cursory inspection when I was last in there but didn't find anything obvious.

I read somewhere that I can short the 2 blue wires to 'over-ride' the thermostat for testing, is that proper?
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Old 02-10-2021, 01:05 PM   #2
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This might offer more info and manufacturers info on sequence of operation and troubleshooting. But if anything turns on, blower motor like you report not sure I'd blame T-stat yet. Suggest reviewing sequence of operation and then troubleshooting.

https://myrvworks.com/wp-content/upl...ing-Manual.pdf
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Old 02-10-2021, 03:38 PM   #3
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For testing so you don't have to run inside and futz with the Dometic controller you can short the T-stat wires together.

The sequence is:

1.T-stat loop has continuity calling for heat.
2. Thermal limit switch has continuity indicating the unit is not overheated
3. Controller turns on air handler/burner blower (they are driven by a single motor)
4. If the Sail Switch gets continuity that indicates sufficient air volume (ducts open, good flow) so it initiates the burner cycle.

So it sounds like you are still having issue with low air flow or the sail switch is sticking or defective.

If after a time out period it does not see the sail switch show continuity the led error code will display a sail switch or thermal switch issue.

Let us know if you get past this and instead have a burner error code.
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Old 02-10-2021, 03:43 PM   #4
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Quote:
Originally Posted by GCinSC2 View Post
This might offer more info and manufacturers info on sequence of operation and troubleshooting. But if anything turns on, blower motor like you report not sure I'd blame T-stat yet. Suggest reviewing sequence of operation and then troubleshooting.

https://myrvworks.com/wp-content/upl...ing-Manual.pdf
Thanks GCinSC2, I printed the manual for my troubleshooting venture.

Apologies for the confusion, I wasn't blaming the t-stat. I just wanted a way to run tests from the outside as I go along rather than having to go into the back of the trailer each time.
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Old 02-10-2021, 03:47 PM   #5
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Originally Posted by BayouBiker View Post
For testing so you don't have to run inside and futz with the Dometic controller you can short the T-stat wires together.

The sequence is:

1.T-stat loop has continuity calling for heat.
2. Thermal limit switch has continuity indicating the unit is not overheated
3. Controller turns on air handler/burner blower (they are driven by a single motor)
4. If the Sail Switch gets continuity that indicates sufficient air volume (ducts open, good flow) so it initiates the burner cycle.

So it sounds like you are still having issue with low air flow or the sail switch is sticking or defective.

If after a time out period it does not see the sail switch show continuity the led error code will display a sail switch or thermal switch issue.

Let us know if you get past this and instead have a burner error code.
Whoops, Brian it looks like you posted while I was answering GCinSC2! Yes, bypassing the t-stat is what I want to do while troubleshooting.

Right now I'm draining the fresh water tank onto the driveway, that will be a hit with the neighbors in the morning
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Old 02-11-2021, 10:44 AM   #6
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Furnace Not Working

I have good reason not to trust my Dometic CCC2 thermostat. I could go on about the 20-page Owner’s Manual and the thermostat’s refusal to reset. So, because my Furnace refuses to activate, I’m not sure where the problem lies. (The Owner’s Manual for my home thermostat—controlling both heating and cooling—is printed on the inside of the battery door, maybe 5 sentences long.) Here’s my question: Has anybody replaced their CCC2 with a simpler home-style thermostat?
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Old 02-11-2021, 10:55 AM   #7
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Dometic installation manual shows you how to wire up a conventional digital or analog thermostat. I suggest you not do that though as the CCC2 features and integration with the furnace and so on all goes away. With a bit of patience, I'm sure folks here can help you through your issues. Do you have a multimeter?

As far as how to use the CCC2 I can help you with that. First off to make it simple to use, ignore all the fancy programming features. If someone has enabled a program, erase it. I can walk you through it. Just let me know how you want to proceed.
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Old 02-11-2021, 01:07 PM   #8
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Same thing happened twice on mine. The limit switch was bad.

The first time I bench tested it and the limit switch started working again. I bought a backup just in case which I used a couple of months later when the same symptoms occurred.

Test the limit switch.
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Old 02-11-2021, 01:52 PM   #9
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Right now it's 28 degrees outside and sleeting. All maintenance is on hold for now! With this cold front coming in I'm just happy that I went out to see if my initial repair was still holding up.

I'll post my questions and progress or discoveries when it's warmed up a bit. Thanks for the input.
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Old 02-11-2021, 06:56 PM   #10
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Quote:
Originally Posted by John & Roberta View Post
I have good reason not to trust my Dometic CCC2 thermostat. I could go on about the 20-page Owner’s Manual and the thermostat’s refusal to reset. So, because my Furnace refuses to activate, I’m not sure where the problem lies. (The Owner’s Manual for my home thermostat—controlling both heating and cooling—is printed on the inside of the battery door, maybe 5 sentences long.) Here’s my question: Has anybody replaced their CCC2 with a simpler home-style thermostat?


I switch to a EasyTouch RV thermostat about 6 months ago. I have been very happy with it and is very easy to install. Check it out at http://www.micro-air.com/kb_easytouch_rv.cfm
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Old 02-11-2021, 07:35 PM   #11
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I switch to a EasyTouch RV thermostat about 6 months ago. I have been very happy with it and is very easy to install. Check it out at http://www.micro-air.com/kb_easytouch_rv.cfm
I guess I'm going to have to look into this thermostat although nothing leads me to believe that is the current problem. The last time I had the furnace open I checked all the connections and it ran fine throughout Janurary. I suspect there is an intermittent in there somewhere.

Micro-Air has some great products, had an Easy-Start on my '18 and put 2 on my current FC. I should buy stock in them!
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Old 02-11-2021, 07:50 PM   #12
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It's not likely there is an issue with the CCC2 controller or the Dometic rooftop control board which contains the relay to provide the continuity indication to the Atwood furnace. My understanding is the furnace receives a signal calling for heat, it just doesn't always fire up the burner. If I have that correct, your issue is with the furnace alone.

The Micro-Air thermostatic controller is nice, but it's $250. It does mimic the CCC2 communication protcol so it is a direct replacement and I do admit it's nicer and easier.
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Old 02-11-2021, 08:42 PM   #13
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Quote:
Originally Posted by GCinSC2 View Post
This might offer more info and manufacturers info on sequence of operation and troubleshooting. But if anything turns on, blower motor like you report not sure I'd blame T-stat yet. Suggest reviewing sequence of operation and then troubleshooting.

https://myrvworks.com/wp-content/upl...ing-Manual.pdf


Troubleshooting Step 1: Tie plastic rectangle thing up with zip tie (I’ll remain convinced this causes most furnace problems)
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Old 02-12-2021, 05:26 AM   #14
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RivetED,

I went back thru your first thread looking for a model number to confirm the POSSIBILITY that this Dometic Service Bulletin addresses and might affect your unit. I didn't see a model specified in your posts.

https://myrvworks.com/wp-content/upl...mit-Switch.pdf

Text from bulletin only.

"All Small & Medium Furnaces (AFS, AFM, DFS, DFM) 73985322 – 81099541
We have been able to identify a non-safety related nuisance issue that is occurring on our Dometic/Atwood
furnaces. This nuisance issue has the potential to occur on all models of Dometic/Atwood Furnace with serial
numbers between 73985322 and 81099541. The nuisance issue enunciates by either blowing the protective
fuse, opening the circuit breaker in the furnace circuit, or rendering the furnace inoperative. Our testing has
shown that in ALL instances the furnace fails in a safe manner.
The cause of this nuisance issue is a mistaken omission of a plastic wire tie to suspend the heat exchanger limit
switch wires up and away from the exhaust tube vent terminal. The omission of this component allows the limit
switch wires to potentially melt on the vent terminal, shorting to ground, and causing either the fuse or circuit
breaker in the circuit to blow, or the sail switch to become inoperative. In ALL cases the safety devices in the
system are performing as designed and prevent the furnace from operating.
Dometic recognizes this nuisance tripping issue is an inconvenience to our OE and potential end-use customers
and we apologize for the extra work that may result. In an effort to try and reduce the amount of work required to
correct this mistake we have designed and tested a field repair for this occurrence which will be more expensive
for Dometic but will make the field repair much easier. The repair will consist of sliding a 6" long, high‑temperature
rated, fiberglass sleeve over the exhaust tube after removal of the vent assembly. The field repair kit will be
available within March, 2018. The field repair kit part # is 31389, Flat Rate Time is .5 and the fault code is 617.25."


If it applies or not, Darren at My RV Works has proved copies of 437 factory service manuals available thru his mobile RV service website plus his actual field repair RV videos on YouTube. This is a good resource to research for help.

Gary
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Old 02-12-2021, 10:14 AM   #15
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Gary that's great, Thank you.

It's just gotten up to 30 degrees here (low ~27) but headed for a couple of single digit days by Sun. & Mon. Right now I'm headed outside to do a complete winterize, hopefully nothing froze last night. I've been keeping the interior at ~65 degrees with all cabinet doors and access panels open. That's with 2 elect. space heaters and a small (12") box fan on the table to keep the air moving.

I printed out the bulletin, again thanks. If my fingers are still functioning when I'm done I'll look for the Furnace mdl #. I'm not sure if I'll open up the front today but I can quickly check to see if those wires have in fact melted on the exhaust tube. I don't need their zip-tie or wire to make a repair

Single digits for over 24 hours straight is quite unusual for central Texas but as the old saying goes; "there's nothing between Canada & Texas than a barbed wire fence in Kansas & that blew down last year", whoever they are
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Old 04-11-2021, 04:19 PM   #16
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So...this is an older post but I just finished fixing the furnace it again. Had some other projects ahead of this but today I tore into the furnace to see if I could find out what was causing it to fail.

I was getting a single flashing LED indication (Air Flow/Limit Fault). I took out the sail switch, nothing obvious and it checked out with my Fluke VOM. I noticed one of the spade connectors on the PCB was not fully seated so I removed the control PCB and as I pulled it out I heard something drop inside the control board compartment.

There was a new, unused white head screw that had been sitting on top of (the back/solder side) of the control board. (Photo attached.)

I fully seated the spade connector, reinstalled the sail switch, and tested the furnace. All went ok, 2 tests. Replaced/mounted the control board, closed it all up and it has passed 3 further tests. To me it's another installation failure, no where do I see a painted white head screw that could be a part of the furnace. My guess is it fell out of someone's hands during assembly of the AS, that's only a guess or SWAG.

Hopefully this is it and we'll have a fully functional furnace for the coming years. If nothing else I know a lot more about the Atwood propane RV furnace (Model # AF MD25141) than I really wanted to but...knowledge is knowledge.

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Old 05-12-2021, 11:37 PM   #17
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Quote:
Originally Posted by RivetED View Post
So...this is an older post but I just finished fixing the furnace it again. Had some other projects ahead of this but today I tore into the furnace to see if I could find out what was causing it to fail.

I was getting a single flashing LED indication (Air Flow/Limit Fault). I took out the sail switch, nothing obvious and it checked out with my Fluke VOM. I noticed one of the spade connectors on the PCB was not fully seated so I removed the control PCB and as I pulled it out I heard something drop inside the control board compartment.

There was a new, unused white head screw that had been sitting on top of (the back/solder side) of the control board. (Photo attached.)

I fully seated the spade connector, reinstalled the sail switch, and tested the furnace. All went ok, 2 tests. Replaced/mounted the control board, closed it all up and it has passed 3 further tests. To me it's another installation failure, no where do I see a painted white head screw that could be a part of the furnace. My guess is it fell out of someone's hands during assembly of the AS, that's only a guess or SWAG.

Hopefully this is it and we'll have a fully functional furnace for the coming years. If nothing else I know a lot more about the Atwood propane RV furnace (Model # AF MD25141) than I really wanted to but...knowledge is knowledge.

Attachment 392995

I had this exact same Airstream, Atwood furnace model, and problem, including the error code. I had similar difficulty removing the cover and exhaust tube and responded in an earlier post on the previous thread, which was very helpful.

After removing the cover, checking the wires/ slightly repositioning them, and inspecting the sail switch I replaced the cover and the furnace has worked worked properly for two days. Since I really did not find a definitive cause for the original malfunction I am not confident the problem is resolved and I anticipate a recurrence at an inopportune time. One of Murphy's corollaries.

Bottom line: thanks for your follow through and photo concerning the screw (foreign object). Next time I open that panel I will check for debris on the board. I should have known to do that based on my experience with numerous repairs to both Airstreams I have owned. Assembly debris is everywhere and poorly finished details are often very sharp, even on common use latches. I almost cut my finger off the first night I owned an Airstream while trying to adjust the table in my 2015 23 FB.

I, too, now know more than I ever expected concerning the Atwood furnace! And I hope I can avoid an unexpected frozen water line due to having no heat when it may be needed on my next trip to Big Bend.
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