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Old 04-18-2017, 08:02 PM   #1
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Atwood Furnace

Had to put the 15amp fuse in and turn thermostat on and the furnace would start. Turn the thermostat down it still keep running even when turned off. Pull the fuse to get it to stop. The previous owner said he had an RV dealer check it out and they replaced the thermostat. Do you think this is still the same problem?? Put the fuse back and the furnace would start back up. Any ideas are welcome. Thanks, Coutch
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Old 04-18-2017, 09:45 PM   #2
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There is a time out on the furnaces for cool down. Meaning once you turn down the T stat, the burner will stop but the blower runs to cool the heat chamber down until a time period expires. And they will also do that time out if you turn the furnace off at the T stat. How long did you wait from turning it off, the blower was running and then pulled the fuse?

As far as putting the fuse back in, which exact fuse was this and where was it located?

Is this in a Sunline, and if so what model camper and year? Atwood made several furnaces and over the years they changed some of the control systems.

If you can get us the model number off the furnace we can look up your exact furnace to give better trouble shooting if the cool down time above is not the issue. If you cannot find the model number, you can pull the grill off outside the camper on the furnace and the model number is generally on a sticker on the furnace out there.

Hope this helps and Welcome to Sunline Owners Club!

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Old 04-19-2017, 11:55 AM   #3
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If the fire does not light the fan will not shut off until the thermostat is turn off perhaps that is what is going on. Does it get hot? When you say "put the fuse back in it runs again" even with the thermostat off? if that's the case in most likely is the control board.
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Old 04-19-2017, 06:28 PM   #4
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Thanks for the information John.
I have a 2003 Sunline 2363 and it has a Atwood 8520 IV DCLP 20,000
When I turned off the T stat and turned it down the furnace was still starting the fuel and the burner didn't turn off as it should when you turn the T stat down. The 15 amp fuse is located in the hall in a box that has all the fuses and breakers. Haven't looked to see how many wires are at the T stat.
Thanks for your information Bill
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Old 04-19-2017, 07:20 PM   #5
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Hi Bill,

OK you gave us some good info to start with. You have one of the newer furnaces.

I'm "assuming" you inherited this problem from a prior owner, is this correct?

If not, did the furnace ever work right for you and then have this problem? Trying to get some history on the issue, new or old problem.

Are you handy with electrical things? either 120 VAC used in the home or 12 VDC used in the autos?

This is what the system is doing and it has to be sorted out where the problem is.

The 85 series, rev IV Atwood has a control board in it that sort of runs the show with the furnace. The T stat tells the control board when there is a call for heat and gets everything else up and going. The furnace really only needs a good signal to run and it is up and going.

If everything is wired correctly, and working correctly when the T stat on/off switch is turned on, the room temp is lower the the T stat, the T-stat itself sends power to engage a relay on the control board that first sends power to the fan motor to start. The blower will run for approx 15 to 17 seconds to purge any left over gas out of the heat chamber.

The blower running creates enough air flow when the battery is high enough in voltage to close a sail switch and allow the burner to light when the time comes. This is a safety to make sure the blower is running fast enough to purge and removed heat from the system. There is also a hi temp limit switch in this to shut down the gas valve if the heat chamber gets to hot.

When the blower timer times out, the blower keeps running and the control board will send power to the gas valve and electrode to create a spark to light the gas. When the electrode gets hot, it sends a signal back that the flame is established and to keep on burning. If the flame sense does not get a signal back in approx 6 seconds, it will shut down the gas valve and electrode and wait for a purge cycle to complete and then try and fire again. After 3 miss fires, it shuts down the gas system on safety until it is reset.

Please confirm the furnace at least does those steps and the burner is up and going in the sequence I described? And confirm when you plugged the fuse back in and the T stat was Off or lower in temp then the room, did the furnace just do nothing until you turned the T stat on and then turn up the T stat to call for heat?

Need to know the system works right or not from a pure power up like what is happening when you plug the fuse back in and send power to the system.

"Assuming" the furnace started correctly and we need to confrim that, here is where something is going wrong from what you have described. Once the system is up and burning in the correct sequence, when the T stat is either satisfied for temperature OR the "on/off" switch on the T start is shut off, then that action should stop the gas valve instantly. The blower will stay blowing until the unit times out and then shut off.

There could be an issue with the T stat, either it is not wired right, not working right, the wrong one or at a last resort there may be an issue at the control board level. But we need some feed back from you first to hone in closer.

Also what exact T stat is on this? Someone may have replaced the factory one from Atwood and put an aftermarket one on that is not working right with the furnace.

After reading this, let us know what is working right and what is not.

Hope this helps

John
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Old 04-19-2017, 07:38 PM   #6
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Hi John,
I'll check the things you commented on tomorrow afternoon. The prior owner told me that he had a problem with the furnace and took it to our local RV dealer and they changed the T stat. I'll also check the T stat for model and mfg. The owner also told me that he was having some trouble with the furnace the last time they used it. The prior owner told me they purchased this unit new and the 13 years they had it they used it only about 5 times. It was always stored inside when not in use. I'll get the info you ask about. As far as being handy with electric, I have some knowledge and have worked with both but not too comfortable. Bill
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Old 04-19-2017, 09:29 PM   #7
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Hi Bill,

More good info. This may be an older issue that is now surfacing.

If by any chance you can take some pics of the T stat and with the cover on and ideally with the cover off so we can see the way they hooked up the wires if you feel OK to take the cover off. You can shut off the 12 volts DC to do this

I found on line the install paperwork for the 85 series Rev IV furnace. See it here: Atwood LITERATURE NUMBER MPD 33179 http://www.atwoodmobile.com/manuals/...0SP%201.08.pdf

Page 5 is a wiring diagram. Pin 5 is the 12 volt power signal from the T stat to control board. When that wire is hot, the furnace gets a "call for heat" and the furnace starts it startup routine. When the signal is pulled, the burner should stop and the blower run long enough to purge. It needs to be ruled out that the signal wire to the furnace is not getting + 12 volts from a source it is not supposed to be. Or the T stat just does not stop the signal. Are you OK using a volt meter to measure 12 VDC? If not, understood no problem. If yes, I can explain how to check for the signal being there and then when it is supposed to be off.

This would basically rule out the T stat, the wiring and then what is left is the control board. But lets get the info from your trip to the camper first as it will help confirm some of what is going on.

Thanks

John
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Old 04-20-2017, 05:37 AM   #8
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Does the fan start instantly or does it pause for several seconds when you first turn the thermostat on?
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Old 04-20-2017, 02:52 PM   #9
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Hi John, Long day running the roads, but I have some of the info you ask about.
The t stat was in the off and temp turned down. Put the 15 amp fuse in and the blower started up and then the gas. I let it run for 5 min turned down the tem and nothing still gas and blower. Turned off the t stat and heard the gas come on shorty after and continue to run then it shut down. Waited a few min and turned the t stat on and the furnace started. Let run three min and then turned the t stat off furnace continued to run and heard gas come on. Let it run 5 min with the t stat off. Then pulled the fuse to shut it down. The T stat is Atwood Hydro Flame Furnace.
Will send photos and volt. Bill
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Old 04-20-2017, 05:43 PM   #10
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It sounds like the delay relay is bad. The thermostat heats a bi metal disk inside of the relay that is where the delay comes from then when the demand is not there the relay cools and shuts every thing off after several seconds. If it stays on then every thing will continue to run it is a mechanical device controlled by the thermostat.
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Old 04-20-2017, 08:43 PM   #11
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Quote:
Originally Posted by Coutch View Post
Hi John, Long day running the roads, but I have some of the info you ask about.

The t stat was in the off and temp turned down. Put the 15 amp fuse in and the blower started up and then the gas.

I let it run for 5 min turned down the tem and nothing still gas and blower.

Turned off the t stat and heard the gas come on shorty after and continue to run then it shut down.

Waited a few min and turned the t stat on and the furnace started. Let run three min and then turned the t stat off furnace continued to run and heard gas come on. Let it run 5 min with the t stat off. Then pulled the fuse to shut it down.


The T stat is Atwood Hydro Flame Furnace.
Will send photos and volt. Bill
HI Bill,

Good detective work.

Need to see pics of which vintage Atwood T stat (they made several) and ideally how it is wired.

The very first problem in blue highlight, the on/off switch was "off", and the heat turned down you put the fuse in and the furnace started. It should of never made it this far and started running with the switch off and the heat turned down. Please confirm, yes it happened like that with the switch off and heat down.

That fact seems to point to 2 areas.

1. The thermostat is wired wrong or has an issue inside of it allowing power to pass through the on/off switch and around the T stat when it is not supposed to.

If it is wired wrong, then hot 12 VDC once the fuse is put in, is sending power directly to the run command wire to the furnace regardless of what the temp of the T stat says. Or there is a problem with that on/off switch sending power to the run command when it is not suppose to.

OR
2. The thermostat is working and not sending a run command signal but the furnace control board has a problem. As soon as the control board gets it 12 volt power on the furnace from plugging the fuse in, it starts running. It is not supposed to do this. This could be a wiring issue at the furnace giving a false run command to the control board or a bad control board.

At this point, the actual T stat side of the thermostat is not controlling or is jumped around by a wiring issue. The pinkish color statement points to this. The overtemp switch may be what is turning the burner off.

My thoughts at this point are:

Trouble shooting will need to be done (by RV tech or other person who can work on the system)

This can be done with a DC volt meter or unhooking wires. Need to confirm there is not a sneak circuit or jumper wire in the T stat terminal area sending power on the run command wire to the furnace

From what you have said, I would start by, unplugging the fuse, identify the furnace run command wire on the T stat, unhook the run command wire from the T stat to the furnace, plug the fuse in. The furnace should not run. If it does "not" run, it points to an issue with the wiring at the T stat or inside the T stat sending power down to the furnace on the run command wire when it is not supposed to.

If it does start, then the issue seems to be at the control board as the run signal is not coming from the T stat. It either somehow got power on the run command wire by being crossed with another power wire or the control board itself has internal issues and in this case, you need to replace the control board.

Once 12 volts is applied to the control board, (plugging in the fuse should do this) the 85 series Rev IV can be turned on and off by using a power jumper applied to the run command wire. You really do not need a T stat to start or stop it. Just give it a run command signal (+ 12 volts) and it will run and stop when you pull the signal.

The need is to figure which area the issue is at, the T stat or the control board area and then drill down to which part not working or which device is not wired right.

Bill, do you feel you can do this, or need to take it to a RV tech? It's your call, no problem on our end taking it to and RV tech.

Hope this helps

John
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Old 04-20-2017, 08:48 PM   #12
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It sounds like the delay relay is bad. The thermostat heats a bi metal disk inside of the relay that is where the delay comes from then when the demand is not there the relay cools and shuts every thing off after several seconds. If it stays on then every thing will continue to run it is a mechanical device controlled by the thermostat.
Hi Main,

What is your thinking on why the furnace started running when the fuse was plugged in with the on/off switch being turned "off"? There was no call for heat as the T stat was turned down and the heat switch was off. It should not be running with the switch off and no call for heat. That seems to be problem 1 wouldn't you think? Did I miss something?
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Old 04-21-2017, 06:08 AM   #13
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Hi Main,

What is your thinking on why the furnace started running when the fuse was plugged in with the on/off switch being turned "off"? There was no call for heat as the T stat was turned down and the heat switch was off. It should not be running with the switch off and no call for heat. That seems to be problem 1 wouldn't you think? Did I miss something?
There seems to be more than one type of 85XX furnaces some use a thermo relay that is heated by the thermostat it supplies power to the board,motor and safety circuits. It is the delay portion for pre and post purge I can't see it from my house but if it is stuck on every thing thinks there is a call for heat. My thinking is it comes on right away no pre purge and never goes into post purge just runs usually if the board is toes up it just won't light. If it has no relay then basically there is a board issue but I'm thinking it does it just makes sense to me it's not a typical board issue. The relay type system to me is a bit strange and kind of lends it's self to problem like he is having.
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Old 04-21-2017, 09:14 PM   #14
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Thank you Mainah, Understand your thought process now.

I used to have a 2004 T2499 and it had a 8525 -Rev IV Hydroflame. I had to take it all apart to correct a problem and I took some good pics then. This is the 25,000 BTU version, Bill has the 2003, 8520 Rev IV 20,000BTU.

I'm going out on a limb here, odds are high they did not change the Rev IV between 2003 and 2004 or it would of ideally had a rev up number. Bills and my prior one had different BTU ratings which changes the orifice in the burner, the burner screen and possible a blower, but the control boards should be the same going by the parts list.

These are pics of my 8525 Rev IV. I did found the older thermal timing relay you are referring to and yes, it works just like you desribe. From what I can find in the master service manual, stating in 7/2001 all furnaces forward use the PC board and not the older thermal timing relay. And mine did not have one and Bill's should not have one.

Here is the furnace itself.




Some of the control board






On this newer unit, the control board runs the show. The hi temp limit is a thermal disk switch and the sail switch is like they had been for a good while.

I believe where Bill's system is at, either the run command from the T stat is being faked on all the time due to a wiring issue or something in the T stat, OR the furnace control board has issues. Ideally this can be isolated to which it is.

If he unhooks the T stat wire at the T stat that sends the furnace run command, then powers up the 12 VDC and if the furnace takes off and runs, either there is a wiring issue some how downstream of the T sat in the run command wiring or the control board has issues.

The control board is not hard to change out in this version, all the wires plug in including the ignition wire. If the run command blue wire is somehow crossed with 12 VDC down stream of the T stat, that could be a search and destroy mission to find out where.

Thanks

John
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