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Old 04-28-2019, 03:11 PM   #1
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Continued Heating Woes!

I must pull the fuse to get the camper heat (furnace) to go off and plug the fuse back in to get the heat to go back on. My HVAC guy checked the thermostat (I already bought a new one!) and said the thermostat is not the problem.



Where else should I look to correct this problem?

1997 Sunline Solaris T2653
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File Type: jpg RV Furnace 2 fuses.jpg (68.7 KB, 3 views)
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Old 04-28-2019, 04:53 PM   #2
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The thermostat is nothing more than an on/off switch. Try this disconnect the wires to the thermostat and see what happens when you put the fuse back in. If it once again runs one of two things shorted wiring or a toes up board.
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Old 04-28-2019, 06:13 PM   #3
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To follow up on mainah's recipe, if you disconnect the thermostat and the furnace still runs non-stop after you put the fuse back in, locate the other end of the thermostat wire at the furnace control board and disconnect that.

If the furnace still runs non-stop after restoring power, the problem is in the control board. If it doesn't, the problem is a short in the thermostat wiring.

If your HVAC guy was on-site, it would have taken him no more than 5-10 minutes to do those checks for you.
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Old 04-29-2019, 08:54 AM   #4
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I would be interested to know if it went through the normal cycle when you put the fuse back in blowing air for awhile then a couple of "clunks" then lighting. It really is not a good ideal to shut the thing down by pulling the fuse because it can not go through a post purge cycle. An ohm meter will tell you right away if the wire is shorted as long as the T stat wires are disconnected. If they are not then it's time for a board Dinosaur replacement boards are top notch. Don't think I have ever seen a board do that but then again I have only replaced a few and they all had the same won't fire problems.
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Old 04-29-2019, 09:50 AM   #5
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Oh gosh, all this is so complicated. The HVAC guy did disconnect the thermostat and the furnace did not shut down. He knows nothing of campers and asked if I could get a wiring schematic for him. He also told me to get advice from the forum.


The furnace does not to thru any cycle when on. It just blows hot air. After about 45 minutes, I pull the fuse again to turn it off.


How can we disconnect the thermostat wire from the fuse board when it is all behind the wall? (There is a little access panel above the circuit board but it really just accesses the water pipes for the shower. It reveals a large wire running up and down; I think that's the thermostat wire, but the opening does not give assess to the back of the fuse board.) I don't want to break open the wall. Perhaps does the whole board unscrew and come out?



When Mainah says, "An ohm meter will tell you right away if the wire is shorted as long as the T stat wires are disconnected," do you mean the thermostat wire disconnected at both ends, or just with the thermostat itself disconnected from the wire?


When you say "If they are not then it's time for a new board," do you mean to replace the entire panel of switches and fuses as shown in the pictures I posted above?


Thanks for all advice.
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Old 04-29-2019, 04:22 PM   #6
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The thermostat wire doesn't go to the fuse panel. It goes to a control board inside the furnace assembly. That's where you would disconnect the other end of that wire in order to see if it's a control board malfunction rather than a shorted wire, if you don't have an ohmmeter to test the wire with.

You get at the furnace assembly via an access panel on the outside of the camper.
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Old 04-29-2019, 05:17 PM   #7
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The wires are behind or inside of the t stat all are a bit different the wires are generally red and white the jacket usually brown. Remove them first make sure they are not touching each other. Put the fuse in if it starts pull the fuse it shouldn't. Next you will have to access the furnace the same wires go to the control board remove one of the wires red or white does not matter. Put the fuse back in and see what happens. If it still starts the board is toast if it doesn't the wire is shorted somewhere rodents?. Again the t stat wires are just like a light switch they are either on or off no in between they have nothing to do with supplying power to anything.
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Old 05-01-2019, 07:03 AM   #8
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Thanks for this information. I'm passing it along to my HVAC guy and see what we can figure out.
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Old 05-01-2019, 07:27 AM   #9
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Here are pictures of the furnace wiring.

Which wire is the thermostat wire?

How could you possibly replace a thermostat wire ... how could you get it from the wall to the furnace apparatus?


What is the "board" that I would replace if the problem is not the thermostat wire?


Thanks again for the help!
Attached Images
File Type: jpg RV furnace inside 1.jpg (84.7 KB, 8 views)
File Type: jpg RV Furnace inside 2.jpg (80.7 KB, 41 views)
File Type: jpg RV furnace inside 3.jpg (78.5 KB, 8 views)
File Type: jpg RV furnace inside closeup 1.jpg (87.1 KB, 47 views)
File Type: jpg RV furnace inside closeup 2.jpg (91.0 KB, 5 views)
File Type: jpg RV furnace inside closeup 3.jpg (89.2 KB, 5 views)
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Old 05-01-2019, 08:49 AM   #10
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The control board we've been talking about is at the extreme left of your pics, next to the switch, oriented vertically. I can't identify the thermostat wires from those pictures. They may well come in to a junction point external to the board, with factory wiring from that point to the board itself.

As for how you'd replace the wire should that be the problem, that can get interesting. The most practical method could be to find some other route than the original to get it from point A to point B.

No offense intended, but given your lack of familiarity with this sort of thing, you would probably be better off having it looked at by someone who's familiar with these systems. Costs money of course, but RVs are kissing cousins with boats. You know, those things usually described as a hole in the water you throw money at.
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Old 05-01-2019, 06:31 PM   #11
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Thanks for the suggestions. No offense taken, believe me I'd love to have somebody who knows what they're doing fix things. However, I'm an older widow with little money, no truck to haul my camper to Camper World (if I could even afford it), and I have to live in this camper with my dog for two more months until my tenants leave my house.



My friend the HVAC guy and I are trying to figure out which wire on the control board/furnace is the T-stat wire. None look small enough. Is there a relay in the air conditioner? That is, does the t-stat wire go to the AC and then thru a relay go down to the control board?









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Originally Posted by Tinstaafl View Post
The control board we've been talking about is at the extreme left of your pics, next to the switch, oriented vertically. I can't identify the thermostat wires from those pictures. They may well come in to a junction point external to the board, with factory wiring from that point to the board itself.

As for how you'd replace the wire should that be the problem, that can get interesting. The most practical method could be to find some other route than the original to get it from point A to point B.

No offense intended, but given your lack of familiarity with this sort of thing, you would probably be better off having it looked at by someone who's familiar with these systems. Costs money of course, but RVs are kissing cousins with boats. You know, those things usually described as a hole in the water you throw money at.
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Old 05-01-2019, 07:03 PM   #12
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The wires are small but there are inside of a jacket they are hard and not flexible like the other ones they will be somewhere near the control board on the left side of your picture. I can not tell you how it interconnects with the AC without seeing it. I would guess it's part of the T stat. A board is around $100 so you really need to find someone that has a clue how the RV stuff works otherwise it can get expensive fast.
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Old 05-01-2019, 07:26 PM   #13
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Quote:
Originally Posted by Aariel View Post
My friend the HVAC guy and I are trying to figure out which wire on the control board/furnace is the T-stat wire. None look small enough. Is there a relay in the air conditioner? That is, does the t-stat wire go to the AC and then thru a relay go down to the control board?
I would think that very unlikely, but my experience with campers is very limited. I'm much more familiar with residential work. I'd spend some time rooting around in the furnace enclosure looking for a cable that's the same as what you see at the thermostat.

On the bright side, you shouldn't be needing the heat for too much longer.
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Old 05-01-2019, 10:55 PM   #14
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Three things stand out to me to check before going further:

1) disconnect furnace thermostat wires at thermostat and put fuse back in. You mayb have done this already, please confirm. The furnace shouldn’t start. If it does, leave the fuse in proceed to step two.

2) the red and black rocker switch on the outside of the furnace. Turn this to the off position. The furnace should go off. I’ve never tried this so I don’t know if it’ll be immediate or do a cool down cycle. Either way, it should sound different and shut down. If not, pull the fuse inside again to shut it down.

3) lift up the couch and there should be a big wood box around the furnace, made out of paneling. There should be screws somewhere to open this. I’ve never had mine apart, but once open, you should see the thermostat wires and power wires coming into there from somewhere. The thermostat wires should look like they do at the thermostat, probably in a brown casing. Follow these to where they connect to the furnace and see if you notice anything that looks like a problem down there.

4) the thermostat leads may have a plug in to the furnace, I’m not sure on this model. If they do, and if it looks like there’s a separate power wire, start the furnace and unplug this plug. This should disconnect the thermostat and wires and the furnace should cool and shut down.

If those four tests fail, I’m going to suspect the control circuit board too. It might be worth calling your local Camping World or RV dealer and ask if they can test your board if you bring it in. I know they have a tabletop devise to test water heater control boards in the same manner. If they can, pull it from the trailer and go have it tested.
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Old 05-02-2019, 12:34 AM   #15
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Quote:
Originally Posted by Aariel View Post

My friend the HVAC guy and I are trying to figure out which wire on the control board/furnace is the T-stat wire. None look small enough. Is there a relay in the air conditioner? That is, does the t-stat wire go to the AC and then thru a relay go down to the control board?
Sorry, I am late to the party... Let me see if this helps

This is for your HVAC guy as he should be able to follow some of this.

First, download this 2003 Atwood Furnace Service manual. You have to be logged in to down load it. Sunline Coach Owner's Club - Sunline Owner's Files - Atwood 2003 Furnace Service Manual

If he goes to PDF page 10, on the bottom right is a wiring diagram called "85-III Local Sense" as that is the number on your model number plate, 8525-III. The rest of the manual explains how the whole furnace works.

Here is a "thought" that I have for him to start with.

Some background first.

On these older series furnaces, they have a timing relay that is controlled by the T stat. It is located on the top right of the blower motor in our pictures. When the T stat call for heat, it sends a signal to the coil on the relay.

The relay coil once engaged, a contact closes to run the blower. This relay also has a on delay timing circuit that creates a timer for the purge time length. The timer creates a pre-ignition purge mode to clear out any left over gas in the heat chamber.

After the purge timer times out, the timer relay contacts close and sends power to a sail switch and to an over temp thermal disk switch wired in series as safeties. If the blower speed is fast enough (it a safety switch) to create the right amount of air through the heat chamber, it will close the sail switch. Power then will pass from the sail switch to the high temp switch that is normally closed. If there is no high temp condition, power then passes to the burner ignition board.

The ignition board on these older ones only deals with the gas burner, the igniter and the flame sense feedback. Once the timing relay, sail switch and over temp switch sends power to the control board, the board takes over and fires the gas valve and the igniter. The heated igniter then sends a signal back to the PC board the flame is on and keeps the gas valve on and the igniter. If the flame blows out, the board senses flame loss and shuts down the gas valve and ignition. It also has a fault circuit on startup if the burner never lights that it will try and light 3 times after a purge time and then go into fault lockout until the system is turned off and on again.

A "thought" on what is going on.

The blower should have gone through a purge cycle before before the gas valve opens and ignition starts. Did it? The burner should not fire off as soon as power is applied to the furnace.

That timing relay may be burnt closed on the contacts. As soon as the power is applied to the furnace, the blower will start instantly as the contacts are welded shut. It would not care if the T stat is on or not. And if the gas valve opens and ignition starts, instantly, then the timing side of the relay has also failed in an on state.

Start at that timing relay to figure out if it is working right and if the T stat is sending a signal or not. There may also be a wire crossed somehow sending a signal to the relay on the T stat line. The entire furnace is 12 VDC.

A few other things,

How the thin T stat wire gets into the furnace

On the top left side of the furnace is a input connection plug. The multi connector plug is clear white milky plastic in color. It barely shows in this pic. The red, yellow and 2 blues go to that plug.


That plug goes through the side of the furnace as a plug for hookup to join, + 12VDC and - 12VDC, the T stat wires. On the outside of the furnace is a detachable plug with a pigtail set of wires on it. Looks like this




The yellow furnace wire in pigtail is - DC neg. It wire nuts to the white camper DC ground.

The red wire in the furnace pigtail is + DC pos. It wire nuts to the black camper DC positive.

The blue furnace wire in the pigtail is T stat. The furnace uses blue as T stat signal. But read the wiring diagram and look at the way yours is wired. One blue may be 12 volt power going out to the T stat (if that T stat needs it) and the other the return from the T stat. The pics above are from a 2005 Sunline which is newer and it may not have the 2 blue wires like the old one you are working on. The newer ones do not have a timing relay, the control board runs the whole show as the board is also updated. The newer furnaces are looking for a ground DC- signal to run. Yours "might" be a looking for a DC +. I cannot tell from here on the older analog T stats.



If you look inside the camper at the back of the furnace on the side with the connector plug, (you may have to remove the air intake grill to get to it), you should see the wire bundle going to the furnace pig tail splices.


That T stat cable does run up to the roof AC unit. At least on the newer ones it does. In the Dometic roof AC control board is a contact that opens up the T stat signal when the roof AC unit is on. It is a safety to not be running the heat with the AC on.

Hope all this helps

John
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Old 05-02-2019, 07:11 AM   #16
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Oh my goodness, I am overwhelmed by your amazing responses. Thank you so much for your help. We have a lot to explore now. I really appreciate your knowledge and these great directions. Thank you. I will let you know how it goes.
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Old 05-02-2019, 08:14 AM   #17
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The timing cycle (pre purge and post purge) is controlled by a heater inside of the relay the relay is part of the control board and basically is not serviceable. Notice the wires in John B's photo, the two small wires (red and white) are the T stat wires remove one from it's connection at the wire nut and try the process again if it does the same thing it's the board.
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Old 05-03-2019, 10:31 PM   #18
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Quote:
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The timing cycle (pre purge and post purge) is controlled by a heater inside of the relay the relay is part of the control board and basically is not serviceable. Notice the wires in John B's photo, the two small wires (red and white) are the T stat wires remove one from it's connection at the wire nut and try the process again if it does the same thing it's the board.
Hi Mainah,

Trying to see if you mixed this older vintage furnace with the newer ones, Or I have it mixed up.

The older furnaces, prior to July 2001, use the stand alone timing relay as per the service manual. Page 16, see here under the relay symbol on the wiring diagram. Sunline Coach Owner's Club - Sunline Owner's Files - Atwood 2003 Furnace Service Manual

After that date, the timing relay is part of the control board. The older timing relay was Atwood part number 31017 which is stated now as no longer available. They are selling aftermarket replacements though.

Point being, it sounded like you stated, if the relay is bad then the "board is bad due to the timing relay that is part of the board". On this 1977 model camper, it would have the separate timing relay and not part of the PC board.

See the relay here on the top right. You can see the motor red lead wire go right to the relay.


OK, do you see this as the board being bad controlling the motor? I agree it could be the timing relay, but as I'm seeing it, the relay is not on the PC board, it is standalone. Or did I miss something?

Thanks

John
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Old 05-04-2019, 10:10 AM   #19
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There are manuals available at this address, they may help you and you technician. https://techsupport.pdxrvwholesale.c...wood-8525-iii/ hope this helps.
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Old 05-04-2019, 07:15 PM   #20
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Well there has to be an interrelation due to the time lag between the fan coming on and an ign cycle. I guess the bottom line if it fires and heats most of the precycle works the problem is it does not know how to turn off pulling the fuse will stop it but there will be no post purge cycle.
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