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Old 10-27-2019, 07:57 PM   #1
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Unhappy 98 Sunline Solarus Trailer, Furnace issue

I have a 98 Sunline trailer that all of a sudden the furnace will not start up.
I turn the thermostat up high, switch is on heat, but nothing happens. I expect the blower to start up and run for a minute or two then the heat to kick in, but I hear nothing and nothing is what happens.
I checked the furnace 12V fuse and it is good. This problem persist whether it is running on 12V or 110V.
When on 110V the fan will run if I switch the fan to "fan" rather than "auto".
Everything else, all lights, Stove, Refrigerator, all work fine. The furnace did work without 110V about 6 wks ago, but not now.



Anyone have any ideas what to check next please respond.
Also, I'm thinking of replacing the thermostat as I have noticed the caliberation is way off when I last used the furnace and I don't trust it. You had to turn the thermo up to about 75 to get it started when it was 60 in the trailer. It wouldn't start placed on 65 or so.
Do I have to buy some kind of special 12 volt thermostat or does any house type thermostat work. I'm thinking they are all low voltage, it that right?


Ralph Louks
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Old 10-28-2019, 10:58 AM   #2
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Hi Ralph,

The next time you are at the camper, take the outside grill cover off and get a pic of the furnace model number and post, or at least tell us the model number.

Something is not adding up on this statement.

Quote:
I checked the furnace 12V fuse and it is good. This problem persist whether it is running on 12V or 110V.

When on 110V the fan will run if I switch the fan to "fan" rather than "auto".
Everything else, all lights, Stove, Refrigerator, all work fine. The furnace did work without 110V about 6 wks ago, but not now.
The fan, if it is working on 110 volts, the fan should work on just the battery assuming the battery is good or at least supply enough power to run the fan. The entire furnace is 12 volts unless someone changed something. The 110 volts runs the power converter and the power converter creates 12 volts that then runs the furnace. If you are on just battery power, the fan should still run assuming the battery is good. Check and see.

Not knowing what T stat and furnace model you have, a simple home T stat "might work" or it might not.

Since you have a fan on and fan auto switch, your furnace must have more than 2 wires coming to it.

Take a pic of the T stat with the cover on it and then off of it. It is possible to just jump the right 2 wires together to fire up the furnace and test that the T stat is the issue. If the furnace runs all good with the correct 2 wires jumped, then you T stat is having issues.

Hope this helps.

John
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Old 10-29-2019, 08:56 AM   #3
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All the info needed for the furnace to do any thing comes from the T stat if there is no AC controls in the thermostat they will only be two wires they are low voltage' a simple test would be to twist the wires together. If it has 4 wires (AC) the red and black will be the ones. Some thermostats did have a small on off lever you might check and make sure that is not turned off. The thermostat is a pretty simple device it really is nothing more that an on off switch and are fairly bulletproof. So the key is no fan that has to be the first thing to happen. It is fused so that would be something to look at. The furnace is strictly 12 volts so it does not need anything other than a good 12 volt battery to make something happen.
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Old 11-04-2019, 09:45 PM   #4
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Okay Mainah and John, here's what I found out. At the bottom of this post should be photos of the thermostat and furnace motor.
First off after taking the cover off the thermostat I found it has 6 wires not 4. They are labeled as below:

label>> +7.5 Cool Fur Hi Fan Fan Gnd
color of wire>> Red Green White Blue Orange Blk

I did not find any on/off lever on the thermostat.
John, I jumped the right 2 wires as you suggested, but as you see it's the Fan and Ground, but it didn't do anything anyway. Also, jumping the Ground and Fur wires don't either. I have no idea what the post labeled 7.5V is?


I checked the 12V fuses, They are all good. The one marked Furnace is 25amp and looked good, I replaced it anyway, no change.

Here's the things I found. With the following settings:

Thermostat switch set to ON. Thermostat temp set to 90 degrees. Batteries charged to 12.3 V. Fan switch set on AUTO.

Results: Nothing happens, even after 5 minutes or so.
Voltage meter readings at corresponding wire screws:
Low fan .5V, High fan 11.3V, Furnace 3.0V, Cool 3.0V

Noted that the Fur and Cool readings of 3.0V seem to climb slowly, see next test below.

What is strange here is that even tho High fan has 11.3 V, the fan does not run.
( note: With this same setup and the generator running, both the low fan and high fan does run and the meter reading at the corresponding post is 12.3V for each) ( Also with generator running the Furnace and Cool posts read 7.5 V, but of course the furnace does not run) This at least tells me that the fan is good.


Thermostat switch set to ON. Thermostat temp set to 50 degrees. Batteries charged to 12.3 V. Fan switch set on AUTO.

Results: Nothing happens, even after 5 minutes or so.
Voltage meter readings at corresponding wire screws:
Low fan .5V, High fan 11.3V, Furnace 7.5V, Cool 7.5V

Of course I would't have expected the furnace to start here and the thermo setting is 50 degrees and the room is 65 degrees at this time, but just noting the meter readings.


I was about to switch to another house thermostat I had, but as you can see with the pictures I'm not sure it will work here. It is a Honeywell with places for 5 or 6 wires. They are labeled from left to right: G, W, Not used, Y, R, Rc. The model may be RTH630081005-0832 but not sure if that is the model number of something else. I have yet to find the install manual for that one that would tell me now the wiring would go.

One other thing, at about the same time that I noticed the furnace would no longer I was replacing my thermostat in my refrigerator. In the process of pulling the wires out of the fridge to the back opening, we not only pulled the old thermo wire out but also pulled the fridge light wire out also. Since I didn't care if I had it anyway (bulb burned out) we just taped up the 2 wires and left them in the back going nowhere but still plugged into the control panel.
Note however from my picture of the control panel that there is a blue wire coming out of the panel in the upper right corner that goes nowhere. It may have always been that way but I'm nervous that perhaps we accidentally pulled it out while working on the fridge problem.
Do you know if this control panel only services the fridge or does it also control the furnace????
If both, perhaps that wire to nowhere is the problem?

The furnace motor is Atwood Mobile Products, model 8525-111

Next are the photos I took starting with the existing thermostat:




Sorry, I don't know how to get the photos onto this forum. I have them on my phone and on ICloud but can't figure out how to imbed them in my message. Please advise.
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Old 11-04-2019, 10:27 PM   #5
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Quote:
Originally Posted by relouks View Post
Sorry, I don't know how to get the photos onto this forum. I have them on my phone and on ICloud but can't figure out how to imbed them in my message. Please advise.
First off, we need to see your pics. See here on how to either "attach" to a post OR how to "link" in pics from a online photo server that is made public viewing.

Forums 101 - posting, accounts, basics


This link will tell you how to upload pics to your personal album you can create. Then if needed you can link the pic from the album to post
Forums 101 - posting, accounts, basics

If you get stuck, ask away. Pics are so helpful in showing us what you are up against.

John
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Old 11-04-2019, 10:54 PM   #6
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It sounds like you have the Dometic heat and cool T stat.

Does it look like this?






If it is, this is the wiring diagram for it.


A few things,

The 7.5 volts is to run the T stat control circuits. It by itself does not control anything, it just powers the T stat control board.

The Fan, deals with the roof AC unit. As does high and low fan. The fan on the T stat has nothing to do with the furnace. The furnace and it's fan are self contained.

If that is your T stat, remove the cover, if you unhook the white FUR wire off the board and then jump from GND to the FUR wire, the furnace should run. The only reason I had you unhook the white wire is, I do not know if there is a back feed into the board if you just jump the terminals.

That jumper takes the T stat out of the system. If the furnace fan does not run after that, this comes down to either the Roof AC unit interlock is not working right or there is a issue at the furnace itself. The AC unit has an interlock so that you cannot run the AC unit and the Furnace at the same time.

Now is where pics come in handy of the furnace motor area with the cover off. The 8525-III I do believe has a timing relay on it to run the fan motor. But I am not 100% sure if later models of the 8525-III went to the fan control on the PC board. Seeing your pic would tell us immediately.

Once we know what your looks like, you can jump the right 2 wires at the furnace itself to simulate the T stat and that eliminates the roof AC unit interlock. The furnace fan is the first thing that turns on. If you have no fan, nothing else on the furnace is going to work.

The fan comes down to,

1. Is 12 volts live at the furnace?
2. Did the T stat signal make it to the furnace to turn on the fan?
3. If you have the T stat signal and no fan, then is power getting to the fan motor? This is where the timing relay comes in or the PC board if your board is newer and has the motor control on it.

Hope this helps

John
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Old 11-05-2019, 11:00 AM   #7
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Furnace issue


Yes John, that thermostat you showed with the photos is exactly what I have. I think I have the photos loaded now. Be sure to notice that stray blue wire on the control panel board I talked about.



I won't be up to my trailer until Saturday to try that wire test you wrote about.


Thanks so much for your help on this.


Ralph
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Old 11-05-2019, 11:20 AM   #8
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Hi Ralph,

Your pics are showing now. GREAT!

I will re-read your post with the pic and respond back later. The furnace you have is the vintage with the timing relay that runs the furnace fan motor.

To the blue wire at the fridge, I'll look up that PC board to figure out what is on that plug. That fridge looks like an RM-2652 model, by chance do you know if it is?

The only thing the fridge and the furnace share in common is the 12 VDC main supply and the 12 VDC negative. Normally they are on separate fused circuits. The furnace since it draws so much 12 volt DC power to run the blower, is normally on its own dedicated 15 amp fuse. The fridge, which also uses 12 Volts DC, is ganged with other 12 volt things on as the fridge does not really use a lot of 12 volt power.

Be back later

John
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Old 11-05-2019, 12:30 PM   #9
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Ok on heat demand you must have 12 volts + (to ground) at the red wire before anything happens. After about 20 sec. the fan should run if it does not fan relay, circuit breaker, broken red wire or bum motor. The fan is the key to the entire adventure once it runs all the other things get to play, air flow proofing, ignitor board, gas valve and the likes. They are dependent on the fan running. Not the other way around.
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Old 11-05-2019, 10:16 PM   #10
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Hi Ralph,

Something dawned on me as I was preparing a note for you, you said this

Quote:
Originally Posted by relouks View Post
I have a 98 Sunline trailer that all of a sudden the furnace will not start up.

I turn the thermostat up high, switch is on heat, but nothing happens. I expect the blower to start up and run for a minute or two then the heat to kick in, but I hear nothing and nothing is what happens.

I checked the furnace 12V fuse and it is good. This problem persist whether it is running on 12V or 110V.

When on 110V the fan will run if I switch the fan to "fan" rather than "auto".
Everything else, all lights, Stove, Refrigerator, all work fine. The furnace did work without 110V about 6 wks ago, but not now.
And then this,
Quote:
Originally Posted by relouks View Post
I did not find any on/off lever on the thermostat. John, I jumped the right 2 wires as you suggested, but as you see it's the Fan and Ground, but it didn't do anything anyway. Also, jumping the Ground and Fur wires don't either. I have no idea what the post labeled 7.5V is?

I checked the 12V fuses, They are all good. The one marked Furnace is 25amp and looked good, I replaced it anyway, no change.
As long as you have 12 VDC power to the camper, either on a charged battery or 120 VAC on a generator or plugged in, when you turn on the furnace on the T stat and the temp setting it high enough to turn on, with your T stat, you should hear a "click" in the roof AC unit. Even if the furnace did not start.

Assuming you heard nothing, no click from the AC unit when you turned on the T stat to furnace, that can be the issue, or at least one of them.

Lets get the basic understanding of what in the camper actually turns on the 12 VDC power to the furnace system. In your system, with that T stat, the T stat does "not" physically connect power to the furnace.

This T stat of yours,




Actually your Tstat only communicates to the roof AC unit control board. There is no wire connection between the T stat and the furnace. I know that may sound strange, but let me explain further as there is no wiring diagram anywhere that shows this.

The Dometic wall Tstat connects to the roof AC control board. On the AC control board is a relay which then connects to the furnace. When that relay is energized, it connects 2 wires from the furnace. One wire is 12 VDC power from the furnace, the other is 12 VDC power signal back to start the furnace. Then the furnace is up and going all by itself. This is part of the interlock I was talking about that you cannot run the furnace and the roof AC on at the same time as the AC unit controls are telling who runs when. Bottom line, if the roof AC unit control board is not working, the furnace will not turn on.

Let me show you in pics. These are from various campers I have worked on to create the right pics to show you. Yours may be slightly different but should not be by much.

Up above the AC ceiling mesh air filter inside is an analog control box. The analog control box looks like this.


Inside that box is a PC board, looks like this.


And the PC board out in the open, looks like this


If you look at the top left corner of the PC board, there is T3 and T4 and the words furnace. Two blue and white striped wires connect to T3 and T4. You can see them on the 2nd pic up too.

Here are those 2 wires hanging out of the box wire nutted to a 2 wire cable heading to the furnace. And not the T stat.


If you are into reading wiring diagrams, see here for the furnace connection.


On your camper, Sunline may have run 2 solid wires from the furnace to the AC control board as opposed to the 2 wire cable. I have seen them do different wiring types over the model years. If you follow those 2 wires down to the furnace, then wire nut onto a 4 wire pigtail plug at the side of the furnace. See here. This is a pic from a 2005 T2363 buried next to a cabinet. Your furnace connection plug may be buried next to some other wall. But your connection plug will be on side of the furnace that does "not" have the copper gas line going to it.


In this case see the 2 blue wires in the plug bundle. Those 2 blue wires splice into the 2 wire thermostat wire cable and run up to the AC unit to hook to T3 and T4 on the PC board. The bundle then plugs into the side of the furnace. The red is + 12 VDC power to the furnace and the yellow is - 12 VDC to the furnace. If you actually jump those 2 blue wires, it will fire up the furnace if all is working on the furnace.




That is how the furnace is wired to the roof AC unit and the AC unit is controlled by the T stat.

OK now the basics, when you turn on the T stat to furnace and it is set high enough to call for heat, did you hear a "click" (only 1 click) of the relay up in the AC unit? Yes/No? If there is no click, no run signal was ever sent to the furnace.

Check and see if you hear that relay click up above the air intake to the AC unit. If you do not have that, by jumpering GND and FUR (unhook white wire and jump to GND) at the T stat wires should turn that relay on. Assuming the AC unit has 12 VDC power. You really do not need 120 VAC to make that furnace relay turn on, only 12 VDC. This then rules in or out the T stat is working and the AC control board is working. If no Tstat action turns on the relay then the T stat may have issues. But jumpering should energize the relay if the board is working.

Now that you know to listen for the click, you can toggle the T stat furnace on and off a few times to make sure you hear it or not.

"IF" you heard the click, then the next reply will tell what to look for at the furnace.

Hope this helps

John
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Old 11-05-2019, 10:48 PM   #11
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Hi Ralph,

This assumes you now made it past the Tstat and the furnace relay click up in the roof AC unit. You have the click, but still no furnace action.

Now we start at the furnace. This will add to what mainah was saying in pics.

I took your pic and drew on it. This topic has some up before and we needed to show a pic explaining this, so it helps you and others.

The pic is "busy" but it will show what we are talking about. Again on "your" vintage 8525-III furnace. Atwood was changing things from the time yours was built up until 7/2001 when the main PC board runs the whole furnace.


Lets start with the basics. That 4 wire bundle connection plug brings in 12 VDC power and GND. And it has 2 blue wires heading to the roof AC unit relay.

Check on the main power circuit breaker between the incoming red (+ 12 VDC) and a yellow wire (- 12 VDC) that you get live 12 VDC power. The Tstat does not have to be on to get this voltage. No power, then figure out why the camper fuse circuit is not sending it.

Assuming you have power to the furnace, then we need to confirm the 12 VDC control signal from the AC unit made it back when the T stat calls for heat. On the circuit breaker is a blue wire. That blue wire is + 12 VDC that goes up to the AC relay. Make sure it has a good connection to send out power. The other blue wire comes back from the AC relay and goes to the fan motor timing relay. When the Tstat is on and the AC relay is on, does + 12 VDC end up at the furnace timing relay? That relay turns on the blower. If you have no power to the timing relay, then the blower motor will not run.

If you have power to the timing relay on the blue wire, then applied 12 VDC turns on a heater coil in the relay. In approx 20 seconds or less, the heat will trip a disk inside the relay and close the contacts to send + 12 VDC the blower motor by the red wire leaving the relay heading to the motor. If you have power to the heater coil on the blue wire and have no power to the red wire going to the motor, then the relay can be bad or the wire connections have issues. The timing relays have gone bad before.

At this point, until you can get the blower to run, nothing else is going to start on the furnace. Try and get you voltmeter on those wires at the plug in terminals to test.

You can jump the 2 blue wire coming from the AC unit to power up the timing relay if needed.

You can also just apply jump 12 VDC to the blower motor directly. Turn OFF the gas valve toggle switch so the gas valve does not open and OR unplug the cable connection from the ignition PC board. The yellow GND is already connected, just pull off the red blower wire from the timing relay and jump + 12 volts the motor direct to test if the blower runs.

Be careful of the heavy red ignition wire, it can bite like grabbing ahold of a spark plug wire, it is high voltage. If you get the motor jumped and running, the sail switch will make and will energize the ignition board if it is plugged in, then after a time period the burner ignition would start clicking. The gas valve switch is off so it will not lite teh burner and you do not want to run the furnace without the timing relay working, that is why I had to unplug the ignition board and or turn off the gas valve.

Hope this helps.

John
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Old 11-11-2019, 10:26 PM   #12
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Quote:
Originally Posted by JohnB View Post
Hi Ralph,

This assumes you now made it past the Tstat and the furnace relay click up in the roof AC unit. You have the click, but still no furnace action.

Now we start at the furnace. This will add to what mainah was saying in pics.

I took your pic and drew on it. This topic has some up before and we needed to show a pic explaining this, so it helps you and others.

The pic is "busy" but it will show what we are talking about. Again on "your" vintage 8525-III furnace. Atwood was changing things from the time yours was built up until 7/2001 when the main PC board runs the whole furnace.


Lets start with the basics. That 4 wire bundle connection plug brings in 12 VDC power and GND. And it has 2 blue wires heading to the roof AC unit relay.

Check on the main power circuit breaker between the incoming red (+ 12 VDC) and a yellow wire (- 12 VDC) that you get live 12 VDC power. The Tstat does not have to be on to get this voltage. No power, then figure out why the camper fuse circuit is not sending it.

Assuming you have power to the furnace, then we need to confirm the 12 VDC control signal from the AC unit made it back when the T stat calls for heat. On the circuit breaker is a blue wire. That blue wire is + 12 VDC that goes up to the AC relay. Make sure it has a good connection to send out power. The other blue wire comes back from the AC relay and goes to the fan motor timing relay. When the Tstat is on and the AC relay is on, does + 12 VDC end up at the furnace timing relay? That relay turns on the blower. If you have no power to the timing relay, then the blower motor will not run.

If you have power to the timing relay on the blue wire, then applied 12 VDC turns on a heater coil in the relay. In approx 20 seconds or less, the heat will trip a disk inside the relay and close the contacts to send + 12 VDC the blower motor by the red wire leaving the relay heading to the motor. If you have power to the heater coil on the blue wire and have no power to the red wire going to the motor, then the relay can be bad or the wire connections have issues. The timing relays have gone bad before.

At this point, until you can get the blower to run, nothing else is going to start on the furnace. Try and get you voltmeter on those wires at the plug in terminals to test.

You can jump the 2 blue wire coming from the AC unit to power up the timing relay if needed.

You can also just apply jump 12 VDC to the blower motor directly. Turn OFF the gas valve toggle switch so the gas valve does not open and OR unplug the cable connection from the ignition PC board. The yellow GND is already connected, just pull off the red blower wire from the timing relay and jump + 12 volts the motor direct to test if the blower runs.

Be careful of the heavy red ignition wire, it can bite like grabbing ahold of a spark plug wire, it is high voltage. If you get the motor jumped and running, the sail switch will make and will energize the ignition board if it is plugged in, then after a time period the burner ignition would start clicking. The gas valve switch is off so it will not lite teh burner and you do not want to run the furnace without the timing relay working, that is why I had to unplug the ignition board and or turn off the gas valve.

Hope this helps.

John
John, I was up to my property in Northern Michigan last Fri & Sat. My main work was in getting my rig winterized and do a little deer hunting. I did get several hours to work on this problem. I will not take the time and effort to try to upload any pictures to this message because the pics you have in this thread are about the same as what I have anyway. The photo you have of the furnace/motor is exactly same as mine. The wires are even twisted around almost exactly as mine.
A few things I found out however or am concerned about I do not have electric service at my property, so everything runs on solar power charged batteries or if need be a generator. I have had a difficult time for the past 6 weeks or so keeping my batteries charged. We have not had much sun for the solar, and it is not nearly as strong this time of year, plus the temperature being cold (20 to 30 degrees last weekend) doesn't help batteries to hold a charge.
So I ran the generator a couple hours and got the trailer batteries (I have 2 of them coupled together) charged to 13.7V. I started checking some of the things you mentioned.

( with running only on battery power)

1. I removed and twisted together the blk gnd wire and the white fur wire on the Dometic Tstat. (With system switch set to furnace) Nothing happened.

2. Returning the wires back to normal, I did get a click from the roof fan area when I moved the Tstat upwards to about 80 degrees. Click on the way up and down.
3. Next I started the generator and tried the same thing as the above step, but moving the tstat upwards to 80 degrees caused the roof fan to start up. Move it below 80 and the fan would shut off. I don't understand why that noisy roof fan would start up when I had it set on furnace and called for heat. I think normal is for the furnace fan to start up, not that roof fan which I thought was only for cooling? If I let it run, after 5 or 6 minutes it will shut off?

4. Okay, back to battery power again, I took the roof fan area apart, took off the cover, the filter, the metal plate on the box, but it was just a mess of wires to me so didn't do anything else it that area.


( I was unable to see pictures you put in the forum and the notations you put on them because I was unable to get Internet there in or around the trailer. Also, the email that gets sent when you reply only has a liink to staticflickr.com which I cannot bring up while at the property either. I did do a print of the email before I went up there so I did have the comments you put before the pictures and the link, but no pics. I am going back there again this coming weekend, so I have printed out the pics on my home desktop and will take those with me.)


5. Going the the picture you sent of the furnace area on the outside. Under battery power I checked for voltage where I could without pulling any plugs apart. On your pic where you have labeled the wires, on the second arrow where you have the red circle, I have that blue and red wire going into a plug. With the system set on furnace, both the blue and red wire had 12.7V at the time. moving Tstat control higher of lower didn't change anything. Generator was running. Without generator, voltage on the two wires is only 11 to 12v at the time of testing.



6. Also, checked the exposed connector for the furnace blower motor timing relay. The top of the relay had 11V, the bottom had none.


7. I did notice that my batteries drain fast in the cold up there, so after a couple hours I do not get good voltage and wonder if that could be a problem. With the generator running, the Furnace wire by the fuse panel will have 13V, but the fur wire in the Tstat will only have 11.4 to 11.8. Is it possible that is not enough to kick in the furnace?
8. Yes, the fridge is model RM-2652. I'm still curious about that blue wire hanging there. I am not sure of the timing, and am not sure that the last time the furnace was working was before I changed the tstat on the fridge or just after. The fridge tstat was changed around Sept 10th.



So I'm going back Friday and can do some more testing armed with the photos now, but any other help you can give me is welcome.
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1998 sunline, furnace not starting


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