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Old 10-18-2011, 11:13 AM   #1
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Duo-Therm Issues

Our furnace has been acting up intermittently for the past couple days. We started using it without issue since Thursday. On Saturday I replaced the original thermostat with a Hunter digital, and it worked great.

Starting Sunday night, it will occasionally not fire when it turns on. It will blow nothing but cold air. I will turn the thermostat down below the current temperature to turn the furnace off, then turn it back up, and it will fire up just fine. It follows this pattern every time it does it. The next several cycles will run just fine, then it will do it again.

I couldn't tell you if this is an issue with propane not being sent, or not getting spark, or anything because I can't reproduce this myself. It is completely random from what I have seen. the best thing I can see is it seems to act up mainly between dusk and dawn. I don't know if it fires up, then stops firing partway through, or what.

This morning we woke up and the fan was blowing, but no heat. It ran for so long we got down to 51 degrees in here.

It is a direct spark ignition model and was manufactured in 1977.

Any help would be greatly appreciated!
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Old 10-18-2011, 01:18 PM   #2
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1) Make sure you do not have any obstruction in the outside intake/exhaust ports like a mud daubers nest that restricts combustion air flow through the unit. That can cause the sail switch to open up.
2) Check the condition and adjustment of the ignitor/monitor electrodes as described in the manuals.

Manuals are located here: Service Documents

The one at the top titled Direct Spark Ignition System Service Guide (http://bryantrv.com/docs2/docs/659/ODSI.pdf) contains general Duo-THerm Troubleshooting and electrode alignment procedures.

For reference, once you turn the thermostat on the blower motor relay should engage providing power to the blower motor. As long as the thermostat is requesting heat the blower motor will continue to run even if the unit did not light. This can run your battery down to nothing. The control board will attempt to light the burner a couple of times then go into lock out mode however the blowwer continues to run until thermostat is turned off.

There are 2 different Duo-Therm Furnace manuals at the link above. You need to just select the one for what you have installed. Blower relay function is the only real difference between the 659 series and 901 series. The 901 series blower relay will stay energized for a short period of time (temp sensor inside) after the burner turns off to cool down the furnace. The 659 series uses a seperate temp sensor fan switch to perform that function.

Dave
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Old 10-18-2011, 10:26 PM   #3
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There was a burnt up section of a nest in the exhaust when we got the motorhome, but all that was removed when we hooked up the propane. I couldn't see anything else in the intake or exhaust after that. Like I said, there was 0 problems up until Sunday night, and while it is random, it appears so far to only happen at night when it does happen.

I understand the workings of the blower and thermostat, which is why I knew to cycle it off and on to try to get it to ignite in the first place.

Most issues listed in my manuals on hand and in those online refer more towards consistent problems, not intermittent ones. I can see where those issues could come into play if you cycle the system and it works, then the next time it gets cool enough to fire, the same problems arise. My system will go 8,10, even 15 or so cycles in between this issue, which doesn't lend itself much to those issues posed.
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Old 10-19-2011, 05:51 AM   #4
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When the furnace is on, make sure the voltage coming from the thermostat is OK. While the blower motor gets it's voltage from the relay, the control board voltage comes via the thermostat. Low voltage can cause problems.

You may be left with only doing preventative maintenace type tasks that may clear the problem up.

1) Clean all electrical connections.
2) Clean and verify electrodes are setup corrrectly.

Dave
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Old 10-19-2011, 08:29 AM   #5
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Intermittent Troubleshooting

What 'Dave78Chief' said twice...

I've worked on my '83 Avion Furnace several times, and am a firm believer - as a lifelong Troubleshooter - in cleaning up contacts and surfaces on blind faith. The high voltage Ignitor lead and contacts and 'clean-ness' to Ground have to be pristine. The high temp environment is tough on components.

Cold 'shrinks' things, including connections. So, it's not unusual for intermittent problems to show up between dusk and dawn [or when temperatures drop for whatever reason]. Check the Ignitor Gap, too. It operates like a Spark Plug. Material at the gap degrades/disappears over time. You can hear it 'click', and see it IF there's a view port. Around the Ground of the Ignitor, it's often corroded from heat. It's a PITA to get to that area, but is worthwhile to clean up. Another key suspect is the Gas Valve, or connections to it, being intermittent. It might be opening for Propane flow sometimes, and not others. Grounds are 1/2 the circuit path, and they have to be good, too.

To prevent dual Battery run-down from my Furnace not igniting, I retrofitted a 'Dinosaur' Control Board. It tries to ignite 3 times, and then times out until manually reset. This is a mixed blessing, since you still wind up cold. But, it saves Batteries, and lets you troubleshoot what has to be fixed anyway.

I removed my Furnace and set up a lil Test Rig. After disassembly and cleaning, I powered it temporarily with an ancient Sears Battery Charger, and safely plumbed it to a 20 lb. Propane Tank. You can make/break the Thermostat connections manually to listen to/observe the turn on sequence. Such a Test Rig outside, or in a ventilated area [Propane sinks], keeps it safe, as does observing safe practices with Propane connections. Take it slow; keep it very methodical.

VERY methodically, omitting nothing, clean up 'everything' on blind faith. I wind up finding the problem 'backwards'. When I take a few corrective actions AND the Furnace then works 100% of the time when cycled manually, only then do I know I found an intermittent problem.

Good Luck!
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Old 10-19-2011, 10:38 AM   #6
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I have also upgraded my old Coleman furnace to the Dinosaur Fan 50 board. It does require some rewiring though in order to implement the blower motor shut off feature on lockout.

Dave
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Old 10-19-2011, 12:43 PM   #7
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Quote:
Originally Posted by SyrenSkywolf View Post
Our furnace has been acting up intermittently for the past couple days. We started using it without issue since Thursday. On Saturday I replaced the original thermostat with a Hunter digital, and it worked great.

Starting Sunday night, it will occasionally not fire when it turns on.
It is a direct spark ignition model and was manufactured in 1977.
Hi

I'm not any kind of an expert like these guys, but from my own experience...
It struck me that your troubles began almost immediately after you installed the new digital thermostat.
If the furnace worked o.k. on the old thermostat, you may have encountered a problem we did in a similar "upgrade"- the new electronic thermostat was faulty. We established that fact by re-installing the old 'stat...

Also, if the new thermostat is programmable, do make sure that you haven't somehow inadvertently "programmed" it to do what it's doing!
That's another mistake that we've made

Good luck

Francesca
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Old 10-20-2011, 09:07 AM   #8
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Breaking Furnace News!

Hee hee, well I got up early this A.M. for a morning ritual that Geezers are known to have to get up for. I heard the Furnace trying to kick on, and failing to do so. So, I gathered up my Tools and a Light and got busy following my own advice above. The Motor to induce a Vent Stack draft was working; the first part of the Furnace turn-on sequence. But, no Heat was 'happening'.

I methodically undid and re-did the various connections on the 25 year old Furnace, hoping it was an intermittent connection. Voila! It started working, and continues to do so on this 43 F degree morning. Further, I saw a little issue of cracked Tubing to the Vent Stack Pressure-sensing Diaphragm - Tubing much like Vacuum Tubing in a Vehicle - so that will be replaced preemptively today.

On the more-important issue above of the RV Furnace:

1. So long as you understand the Circuit and Schematic, making and breaking the Thermostat connection manually will bypass the new Thermostat and reveal if the new Thermostat is related to the Furnace problem. This is part of what I do in the Test Rig/Troubleshooting scenario mentioned above, or if the Furnace is still installed while Troubleshooting.

2. I, too, had to modify the Dinosaur Board during retrofit. At issue was the fact that my Furnace made and broke the Thermostat Ground connection; not the + voltage connection. This detail mattered. Dinosaur Staff were superb in helping me trade ideas via e.mail to adapt their Board to the 'reverse' way my Furnace was controlled.
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Old 10-31-2011, 07:53 AM   #9
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Ok, I have an issue, and wanted some input on it. I want to pull out the furnace to give it a thorough cleaning, check out the blowers/fans and make sure there are no obstructions or anything needing to be replaced. I'm feeling air coming from there, too, so I want to ensure everything is sealed properly.

My issue at hand is the propane line. About 3-4" comes in through the side of the furnace housing to attach to the furnace (you DuoTherm owners know this). Where it leaves the housing, it curves back towards the back/top, leaving about 1/2"-1" of play room before hitting the wall. It then crosses over the top, and down the other side where it proceeds to the floor about 8 inches or so below the furnace. There are no disconnects anywhere but on the furnace itself. There is just enough gap around the furnace housing and the wood to see this if you shine a flashlight just right.

It looks like they installed it before they finished the enclosure. Short of cutting the propane line and reinstalling that, I can't see a way to remove the furnace without busting up the wall of the closet and the bench seat attached to it.

I could try adding some pictures later if need be. Any thoughts on the matter? Could I viably pull everything apart enough to clean everything without removing the furnace? I want to clean out the empty space in the back 1/2 of the furnace where the blowers are, as there is mouse droppings and who knows what else back there from before we purchased the mh, and ensure everything is sealed.
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Old 10-31-2011, 09:07 AM   #10
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Whether new or old, RV mfg's were never known to make repair/maintenace things easy. Only way you can do this right is to remove the furnace. Typically, the propane lines drop under the rig and route between the frame rails. If there is no slack to allow disconnect and removal, you may need to locate a flexible replacement line to replace the existing installation.

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Old 10-31-2011, 12:38 PM   #11
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Quote:
Originally Posted by SyrenSkywolf View Post
Ok, I have an issue, and wanted some input on it. I want to pull out the furnace to give it a thorough cleaning, check out the blowers/fans and make sure there are no obstructions or anything needing to be replaced. I'm feeling air coming from there, too, so I want to ensure everything is sealed properly.

My issue at hand is the propane line. About 3-4" comes in through the side of the furnace housing to attach to the furnace (you DuoTherm owners know this). Where it leaves the housing, it curves back towards the back/top, leaving about 1/2"-1" of play room before hitting the wall. It then crosses over the top, and down the other side where it proceeds to the floor about 8 inches or so below the furnace. There are no disconnects anywhere but on the furnace itself. There is just enough gap around the furnace housing and the wood to see this if you shine a flashlight just right.

It looks like they installed it before they finished the enclosure. Short of cutting the propane line and reinstalling that, I can't see a way to remove the furnace without busting up the wall of the closet and the bench seat attached to it.

I could try adding some pictures later if need be. Any thoughts on the matter? Could I viably pull everything apart enough to clean everything without removing the furnace? I want to clean out the empty space in the back 1/2 of the furnace where the blowers are, as there is mouse droppings and who knows what else back there from before we purchased the mh, and ensure everything is sealed.
Hi-
I'd be reluctant to remove a properly functioning furnace unless I absolutely had to- if you can see the mouse droppings, perhaps you could adapt a piece of hose, attach it to your vacuum cleaner, and clean them out that way...
The air you're feeling in the furnace area is likely just coming in through the vent, as it's supposed to. Your furnace uses outside air for combustion so that you get to use all the inside air for breathing!

But if you do decide to go ahead and pull it out:
It's been an RV "code" for many years that all propane connections must be readily accessible even once the unit is completed.
That means that the only part of the propane system that's "permanently" sealed/concealed behind walls etc will be uninterrupted gas lines.
I can't see any advantage to tearing out walls etc. to accomplish removal...

Cutting the line and replacing it with flex type line may also be a problem.
Many if not all flexible gas lines aren't approved for permanent installation in RV's, solid piping continuing as the industry standard.

Hope this helps...

Francesca
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Old 10-31-2011, 04:26 PM   #12
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That's the big issue, is while most of the time it functions fine, sometimes it doesn't, which is why I want to remove it to check it out.

If it was completely fine, I would leave it as is.

I guess the big thing is, is if I were to cut the line, how would I go about it, in the safest way possible? I may just end up leaving it until I have money to either replace it or have someone else pull it and fix it. Haven't decided yet.
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Old 10-31-2011, 05:52 PM   #13
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I just read back through the thread, and don't see a post from you as to whether you solved the problem you originally asked about...
You'd stated that the furnace had no issues until you installed the digital thermostat...maybe I misunderstood, but I took that to mean that the furnace functioned o.k. before that change.
If that's true, my hunch is that functional problems are related to the thermostat change and not to the furnace itself.

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Old 10-31-2011, 05:57 PM   #14
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At a minimum, I would clean and adjust the electrodes as described on page 2 and 3 on the manual I linked to above. If wrong it will create the problems you are having. They are normally accessable via an inspection window.

Dave
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