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Old 06-30-2018, 09:01 PM   #1
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Atwood 7900-II Not staying lit. 1 flash w/ 3 second pause.

I have an Atwwod 7900-II in my 2010 23' Flying Cloud. The furnace come on and blow hot air for a while. Then it shuts off and won't turn back on. I removed the cover and there is a single red light flashing. According to the manual it is a "limit switch/airflow problem". Has anyone ever had this problem and if so how did you fix it?

Thanks
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Old 06-30-2018, 09:52 PM   #2
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Quote:
Originally Posted by veg hed View Post
I have an Atwwod 7900-II in my 2010 23' Flying Cloud. The furnace come on and blow hot air for a while. Then it shuts off and won't turn back on. I removed the cover and there is a single red light flashing. According to the manual it is a "limit switch/airflow problem". Has anyone ever had this problem and if so how did you fix it?

Thanks

Yup, I'll look for the thread. I think it's on the 20 footers thread,


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Old 06-30-2018, 10:24 PM   #3
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Search for”sail switch”. That’s the gizmo that senses combustion air flow. If it’s not working, it will not fire up
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Old 06-30-2018, 11:40 PM   #4
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The short answer/solution is the last link

http://www.airforums.com/forums/f427...-165259-2.html
posts 1577 and follow up 1623

http://www.airforums.com/forums/f542...27845-128.html
post 1783

final fix…almost
http://www.airforums.com/forums/f542...27845-131.html
post 1829

http://www.airforums.com/forums/f542...27845-137.html

post 1914….finally. with pics of the culprets!!!!


Repair update: Furnace. Seems not only was the sail switch bad but so was the ignition electrode. Images attached in case you've never seen one. Determined this repair is not an owner fix OTR as the furnace needed to be removed.

Heads up, it looked like the local dealer used a crow bar to remove it (a whole other story). Make sure you look at it with the cover removed
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Old 07-01-2018, 08:53 AM   #5
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Quote:
Originally Posted by CruizinDux View Post
The short answer/solution is the last link

http://www.airforums.com/forums/f427...-165259-2.html
posts 1577 and follow up 1623

http://www.airforums.com/forums/f542...27845-128.html
post 1783

final fix…almost
http://www.airforums.com/forums/f542...27845-131.html
post 1829

http://www.airforums.com/forums/f542...27845-137.html

post 1914….finally. with pics of the culprets!!!!


Repair update: Furnace. Seems not only was the sail switch bad but so was the ignition electrode. Images attached in case you've never seen one. Determined this repair is not an owner fix OTR as the furnace needed to be removed.

Heads up, it looked like the local dealer used a crow bar to remove it (a whole other story). Make sure you look at it with the cover removed
Thanks for posting all this! So I'll replace the sail switch and go from there. When you say it's not an owner fix OTR what do you mean? On the Road? The part is $7.75 on amazon. Is this the same one?

https://www.amazon.com/Atwood-36680-.../dp/B004QMX9WY

I plan on doing it myself because I'm in the middle of nowhere and I don't plan on paying some knucklehead $150 an hour. Thanks for the help.
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Old 07-01-2018, 09:00 AM   #6
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Quote:
Originally Posted by rmkrum View Post
Search for”sail switch”. That’s the gizmo that senses combustion air flow. If it’s not working, it will not fire up
It's firing up and works well for a while. Then it shuts off and won't come back on. When I take off the panel after all this is when I see the red blinking light.
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Old 07-01-2018, 10:56 AM   #7
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Veg hed, this is for memory but i think the sail switch is accessible, once the board is removed, but apparently i also needed the igniter which requires pulling the furnace (according to the dealer making repairs under warranty)

This failure happened while returning home, so it wasn't imperative to deal with the lack of furnace heat asap....we used the HP a little, but the weather helped by being moderate.

If i was out of warranty, like you i would have tried the OTR sail switch replacement first.

It would be great if you could post pics of the sail switch removal.
Bob


Quote:
Originally Posted by veg hed View Post
Thanks for posting all this! So I'll replace the sail switch and go from there. When you say it's not an owner fix OTR what do you mean? On the Road? The part is $7.75 on amazon. Is this the same one?

https://www.amazon.com/Atwood-36680-.../dp/B004QMX9WY

I plan on doing it myself because I'm in the middle of nowhere and I don't plan on paying some knucklehead $150 an hour. Thanks for the help.
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Old 07-01-2018, 11:32 AM   #8
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Darn, timed out on the edit...




[edit...it should be noted that after reading back I too had the 1 flash ~ 3 second pause which indicated the limit switch (= sail switch I believe). The dealer replaced the limit switch, then diagnosed/replaced that igniter switch as it would still not fire. You too may be in the same situation. Like I said above, I too would replace the limit switch as it appears to be an owner OTR fix. Obviously if it doesn't fire after replacement of the limit switch then one would need to decide to see the pro or owner repairs. Personally I'd except under extreme circumstances (cold and no heat at all) attempt removing the unit and dealing with the gas connection.


AS a side note I bought a 1500 watt portable ceramic space heater that we used on the last trip. Kept it on low and had better sleep not missing the roar of the furnace.



Good luck and keep us posted.
Bob
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Old 07-01-2018, 11:38 AM   #9
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Do not replace parts as a means of figuring something out !!!
Buy quality multimeter and operate the sail switch manually , if the meter does not indicate the switch is working then replace / same with any problem - test & confirm a part is faulty --- parts swapping is an ignorant way to fix something , learn some basic's and save more & fix most issues .
The most common failure of furnace / sail switches is the lack of the manufacture to put a screen over the intake & exhaust - muddobers - bugs go into the openings and make a nest - blocking the movement of the sail - stopping the switch from working .
Any repair can be done by anyone willing to learn .
Now I can understand that if your well off [ time & money ] then you may not want to bother .
But believing the bs from the manufacture of anything - that only there people can do service / repair , is just bs .
Do not be part of the problem - learn some basics and almost anyone can service / repair most things they own - there has been an [ almost underground ] wright to repair - https://www.economist.com/business/2...ement-tools-up
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Old 07-01-2018, 11:49 AM   #10
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Quote:
Originally Posted by veg hed View Post
I have an Atwwod 7900-II in my 2010 23' Flying Cloud. The furnace come on and blow hot air for a while. Then it shuts off and won't turn back on. I removed the cover and there is a single red light flashing. According to the manual it is a "limit switch/airflow problem". Has anyone ever had this problem and if so how did you fix it?

Thanks
Quote:
Originally Posted by veg hed View Post
It's firing up and works well for a while. Then it shuts off and won't come back on. When I take off the panel after all this is when I see the red blinking light.

I think the furnace is over heating and a safety mechanism (limit switch/internal thermostat) is sending the signal to the board.
Before disassembling to check the sail switch, check a couple other things. Look inside the exhaust port to see if there are any dauber nests blocking the exhaust. Blockage in the exhaust port might give the same red light blinking signal. Overheating could also be caused by a blockage on the air return inside. (like a mouse nest)
The reason I offer these suggestions: you said the furnace ignites and runs for a while. A non functioning sail switch would not allow ignition.

ps:
In both of my trailers, I can access the sail switch to check function without removing the furnace. They are 8500 series.

ps2:
Remove the 4 screws that surround the exhaust port, then the exhaust port cover will slide out, giving you access.
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Old 07-01-2018, 06:38 PM   #11
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Quote:
Originally Posted by A W Warn View Post
I think the furnace is over heating and a safety mechanism (limit switch/internal thermostat) is sending the signal to the board.
Before disassembling to check the sail switch, check a couple other things. Look inside the exhaust port to see if there are any dauber nests blocking the exhaust. Blockage in the exhaust port might give the same red light blinking signal. Overheating could also be caused by a blockage on the air return inside. (like a mouse nest)
The reason I offer these suggestions: you said the furnace ignites and runs for a while. A non functioning sail switch would not allow ignition.

ps:
In both of my trailers, I can access the sail switch to check function without removing the furnace. They are 8500 series.

ps2:
Remove the 4 screws that surround the exhaust port, then the exhaust port cover will slide out, giving you access.
I checked the exhaust port. It's clean and there is hot air coming out when the furnace is running. Where is the air return?
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Old 07-01-2018, 10:18 PM   #12
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Quote:
Originally Posted by veg hed View Post
I checked the exhaust port. It's clean and there is hot air coming out when the furnace is running. Where is the air return?
The air return is usually a slot in the cabinetry right in front of the furnace, at floor level. There is no grill or filter, just an opening at the furnace. Dust, hair, and other small items can get in there and restrict air going in. The fan can get clogged with this stuff. Also looked for anything blocking or clogging the outlet ducts. Also a crushed duct inside a storage area is possible.

Even if looking straight back into the exhaust port seems to be open there still could be a partial blockage. If you have a small mirror or bore scope, try to look around the first bend inside the tube.

Next step would be to check the function of the limit switch/thermostat. It could send a false signal if it is failing. Depending on where it is located, the furnace might have to be taken out and tested on a workbench.

Next step, sail switch.

Next step, circuit board.

When the combustion / ignition areas of the furnace start being disassemble, it is time to get professional help.
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Old 07-02-2018, 06:22 AM   #13
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Quote:
Originally Posted by A W Warn View Post
The air return is usually a slot in the cabinetry right in front of the furnace, at floor level. There is no grill or filter, just an opening at the furnace. Dust, hair, and other small items can get in there and restrict air going in. The fan can get clogged with this stuff. Also looked for anything blocking or clogging the outlet ducts. Also a crushed duct inside a storage area is possible.

Even if looking straight back into the exhaust port seems to be open there still could be a partial blockage. If you have a small mirror or bore scope, try to look around the first bend inside the tube.

Next step would be to check the function of the limit switch/thermostat. It could send a false signal if it is failing. Depending on where it is located, the furnace might have to be taken out and tested on a workbench.

Next step, sail switch.

Next step, circuit board.

When the combustion / ignition areas of the furnace start being disassemble, it is time to get professional help.
Yep, I took off as many panels as I could without removing the furnace. I checked the exhaust port and the intake return. The furnace itself looks clean and there is no debris or blockage anywhere. And the ducts are straight with no blockage. I'm thinking it has to be some kind of failure on the limit switch, sail switch, circuit board etc. I am looking at purchasing one of these kits:

https://pdxrvwholesale.com/products/...ii-tune-up-kit

For $70 including shipping I can tune up the whole furnace. It is 8 years old and this looks like a cheap option to update a lot of stuff while it is out.
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Old 07-02-2018, 11:57 AM   #14
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Veg Hed, not sure if it matters but you indicated a 7900-II (which is also my model in the 2014 FC 20) and this kit is for a 7020-II. Great price and a great kit. Just a heads up.


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Old 07-02-2018, 11:28 PM   #15
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Veg Hed, not sure if it matters but you indicated a 7900-II (which is also my model in the 2014 FC 20) and this kit is for a 7020-II. Great price and a great kit. Just a heads up.


b
VH, my mistake.(and typo) looks like the 7900-8212 follow the same parts schmetic.
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Old 07-08-2018, 10:18 AM   #16
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Veg hed, did you finish repairs?
Bob
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Old 07-08-2018, 10:35 AM   #17
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Not yet. I’m working a lot now but it’s on the list. I have a 7920 so the kit should work. I’ll keep you posted.
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Old 07-08-2018, 12:58 PM   #18
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Not yet. I’m working a lot now but it’s on the list. I have a 7920 so the kit should work. I’ll keep you posted.
Thanks. I'm very interested on what can be done w/out pulling the furnace. The dealer i presume pulled to test on the bench and rule out daubers. It would be great to know the owner OTR in place options.
Happy trails.
Bob
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Old 07-20-2018, 11:19 AM   #19
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I finally got around to swapping out some of the old parts today. I switched the Limit switch, Sail Switch, Electrode, Electrode Gasket and Igniter Lead wire. I was going to switch out the Burner Assembly but it looked like a little more than I was comfortable getting into. I pulled the furnace out but did not disconnect the wires. This gave me room to work on the furnace on the Airstream floor.

To swap it all out took me about 1.5 hours. The new sail switch looked similar but the sail part was smaller. I reinstall the furnace, tested for leaks and all was well. Turned on the propane and the furnace fired right up and ran for about 20 minutes. I'll test it this evening to make sure it goes on and off with the thermostat. Then I'll reseal the outside vent.

Oh yeah, I highly recommend this kit from PDX RV. It also came with a CD-Rom with more manuals than you'll know what to do with.
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Old 07-20-2018, 11:52 AM   #20
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Veh Hed, great feedback and pics. Thanks


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