Suburban NT 40.
At my wits end.
It starts normally, runs good for a few minutes, then the flame goes out. The Dinosaur board tries 3 times to relight like it is supposed to, then it shuts down after the fan runs for a few minutes to cool down. I have gone through everything such as the igniter/flame sensor, limit switch, sail switch, etc. The flame looks good and strong and blue. The motor runs strong. The only thing different is the propane tank got overfilled on our way down South this winter, and it seems like the trouble started after that. What if it buggered the pressure regulator at the tank? What is puzzling though, is that all the other propane appliances work fine (generator, cook stove, fridge, water heater).
So I am thinking maybe the gas valve. There are two solenoids on it. Maybe one is weak and doesn't stay open?
Or the flame sensor/electrode is bad, even though it sparks normally and I have verified that it is adjusted correctly.
The intake and exhaust aren't obstructed.
Ideas?
TIA.
JC
Is your battery voltage good? 12.25 or better?
Lost,
Are you in Canada or down here where the weather is above freezing? That may or may not matter. Just asking.
It is not a Dinosaur board of it uses the 3 strikes and your out rule. My 1967 motorhome had a 1 strike board in it and I upgraded it to a 3 strike board. It also runs after it shuts down which the old furnaces did not do.
If the other appliances work I would suspect the circuit board or the regulator on the unit. But then again, the furnace probably draws more propane than the other devices so your tank regulator may be the problem.
We had a problem with Buck Trouts propane at the rally and someone else had a spare regulator. We swapped it out but that didn't help, but we pretty much ruled out the regulator. If you have a friend with a spare or installed regulator I would swap it out to determine if that was the problem. Otherwise regulators are pretty cheap and you can buy one to test out. As you live where it gets a bit chilly, it never hurts to have a spare on board anyway. You can get them in most towns pretty easy.
Otherwise you can start throwing parts at the Surburban and eventually it will probably work.
One last thing you can which is free is to try is to disconnect the line and blow air thru the line to ensure it is not blocked with crud. That is what was wrong with Buck's line. Blew a bunch of mud right out of it. This is pretty easy to do if you carry an air hose.
If you still do not get it to work, come to Pahrump this weekend and 10 of us will tell you what to do. :D (http://:D)
Thanks Gary!
We are back home, and it is still winter :(
I will blow out the line to the furnace. Good idea, and free.
Next I guess I could swap regulators. The one on the tank is a 2 stage. Does it have to be a 2 stage? Could overfilling the tank have pushed crud into the regulator and partially plugged it? The attendant at the gas station didn't open the spit valve and filled the tank to 100%. I wasn't paying attention, assuming he knew what he was doing... Wrong!
JC
HIGH TEMP LIMIT. May be defective and thinks it is seeing a burner box over temp....I would definitely check it.
Surely it has one...
My guess is air in the line. air is lighter than LP ( thanks Jack so the air plugs up the line with an air bubble that won't move and doesn't let enough gas through to keep it lite. Open the little thumb screw on the line by where it connect to the burner if there is one. Open it a little with the gas on but switch off and bleed some out. close it let the air clear. then try to start it again. other wise it is your board. If you get a Dino board get the remote board to. You just hook it up away from the heater so it won't happen again. The heat messes with them because they are inside the unit.
Edit Lp is not lighter than air Like I originally stated. Air is lighter than LP as per Jack below informed me that was backwards. Noted and corrected above. sorry JC. But the rest is correct.
Hi JC, if liquid gets to burner from over filling, it can gum up the works, propane units have to burn gas, this came from Vegas propane, after a similar problem, could affect the stove or fridge or heater, one or all, or sail switch that you already checked, tom...
Dave, I think you meant to say that propane LPG is heavier than air -- LPG has a specific gravity of 1.55 while air has a specific gravity of 1. I'd agree with the rest of what you said. If I miss read your meaning let me know. Jack
Thanks Jack yep My bad. Thats why I keep you around Jack, LOL ;D
make sure there are no spider webs in air intake. common problem over the years.
Shut off all points of ignition,, then open the "spitter valve" and leave open till no liquid comes out..(only gas) Then try again.>>>Dan
Thanks. Tomorrow I will try purging the gas line. I will see if there is a bleed screw. I already checked the high limit switch, so I don't think that is the problem. The tank is about half full now because we have been using the other appliances. I'll post tomorrow about my progress.
JC
JC heat is so over rated anyway. Tomorrow it will be 72 F ::)why do you need heat?.. Kidding you. ;D Say hi to the Boss for us.
Dave
Well, I disconnected the gas supply line and blew it out. No crud, it was clean. I removed the regulator and took it apart. Seems clean and in good order. This afternoon, I will double check that there are no obstructions in the return air ducting, and all the vents. I have already checked the combustion intake and exhaust and they are clean.
The furnace starts normally and runs good for 5 minutes or so until it shuts down every time. Could the flame sensor be bad? But if it was, I would think it would shut off immediately after lighting, or not even light up? The igniter/sensor wire seems good, as well as the connections. I will double check that too.
Will report back later.
JC
There's not much for a chimney on those but is there any chance there's some kind of blockage there?
All ducting is clear. So is the intake and exhaust. I looked at the sparker/flame sensor again. The ground rod was loose on the base plate. So, with nothing to loose, I tried welding it and burned right through... So went to town to the RV dealership to look for a replacement. They didn't have one, so it is ordered and won't be here till Thursday. Will go from there...
JC
JC, these appliances only last about 10 good years anyway. After that they get finicky. This not something you want to go bad while on the road so I think it is a good idea you decided to just replace it. Then you won't have to worry about it for another 10 years. You may even end up with a more efficient unit. After you get it, it should be about a 10 minutes job to pop the old one out and put the new one in and caulk around the outside. :D
If you bring it down to the Pahrump Rally, I will help you pop it in. ;D
is there a sail switch ?
My bet would be on the flame rod. When I was in the business, shutdown after a few minutes of operation was usually either a failing flame rod or a cracked heat exchanger. Here is how the rods work:
https://electronics.stackexchange.com/questions/148405/how-does-a-flame-sensor-or-thermocouple-operate-with-just-one-wire
TOM
Hi JC, older units had a thermacoupler, with a pilot light, if it has one, that would also be an issue, easy replace and inexpensive, tom...
Donald, the sail switch is good. I have tested it, as well as the limit switch.
Oldmansax, we will find out later this week when the new flame sensor arrives. I hope that it fixes it. Thanks for the link about how it works. The fire box/heat exchanger is good too. I looked at it.
LV Tom, it has electronic ignition with a sparking igniter controlled by a Dinosaur circuit board, which I believe is good, as it does what it is designed to do, with the little light doing its green and red thing.
If that new flame sensor doesn't fix it, I might drive the bus over a cliff... I don't know what else to do.
When driving home from down South last week, we had a propane catalytic heater overnight. The last night in Montana where it was colder, I ran the generator all night and had 2 electric heaters upstairs, and one light bulb in each baggage bay to keep the plumbing from freezing. When we get out of bed in the morning, I turn on the engine block heaters (2) for some time while we make coffee, etc. The geny is 6.5 kw. I wish it was bigger so I could run more electric things simultaneously. Like a 12kw would do. Or how about two 20kw generators like in some of the entertainer buses...
JC
Since it is pushing towards warmer whether now, if you can't figure it out, just get a new unit. As said before-they don't last forever. Good Luck, TomC
Quote from: lostagain on March 28, 2018, 07:21:44 AM
Donald, the sail switch is good. I have tested it, as well as the limit switch.
JC
just tossing out clues :)
New igniter/flame sensor didn't make a difference. Today I will hook up a 20lb cylinder for a supply to verify that the propane in the built in tank isn't contaminated. Although all other appliances work fine. I will re-check everything as per the troubleshooting chart. Let you know.
JC
The 100 dollar gas valve is bad ???
Sure could be luvrbus. I just replaced the 40 year old gas valve in my little bus-----and not a week later the same exact gas valve in the granny flat at my house!?! Jack
Could be the gas valve. I have bench tested it by putting 12V to it. I can hear the solenoids click. I have taken it apart and it looks clean. Re-installed in the bus, the furnace will run forever with the end cover off, but shuts down after a couple of minutes with the cover on. So somethings gets hot and tells the board to shut down. And it is not the limit switch, because I have bypassed it to prove that. The gas just turns off and the light on the Dinausor board goes from red to green (red is gas on, green is gas off fan only). So I suppose a solenoid valve would let go when it gets too hot? Puzzled...
JC
If the board is inside behind cover, move it out of there with jumpers, if necessary. Common for electronics to pull that crap with a component breakdown.
Make sure that the exhaust and fresh air intake going thru the outside wall are in place and no cracks or pinholes, and no obstructions to airflow. Also make sure the combustion air blower wheel is free of debre, no broken/bent or missing fins.
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JC just info do you have and did you check the fuses in the thermostat and on the board in the unit?
Took it all apart, again. Everything checks out. I have it narrowed down to this: run good with end cover off. Shuts down the gas valve within a couple of minutes once I put cover on. That is the housing cover that goes in front of the igniter/flame sensor. I don't think it affects air flow because it would trigger the sail switch and it doesn't. Combustion air is isolated from forced air side, and doesn't get affected. The combustion air wheel is good and clean, so are intake and exhaust.
Maybe the increased heat after putting the cover on affects something?
I'll look at all the wiring. I am wondering about the igniter wire. Looks good but maybe the increased heat makes it not conduct anymore, telling the board there is no flame?
There is another Suburban furnace in the horse trailer. I could swap igniter wires. I could swap control boards too, to make sure I don't have a board issue.
I'd like to find the problem. I'd hate to give up and buy a new furnace...
JC
Yep swap the boards to see. I will bet it is the board. a little burnt resister or diode would do it and you can't tell by looking at it.
The 2 main components prone to the type of thermal failure you are describing are the control board and the solenoids. You would be surprised just how sensitive those little solenoids can be. I was working in a shop outside sacremento last year and one of the techs working on a furnace on the bench was pulling his hair out becuase no matter what parts he threw at it he could not get it to stay lit lomger than about 30 seconds or so. I casually walked by and slid the exhaust tube on it and he couldn't stop shaking his head and saying "i cant believe thats all it was"
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I'll go with thomasinnv and Clifford's advice and order a gas valve. I'll let you know when I put it in.
JC
Bingo!
I got a new gas valve, and it works really good now. I guess the valve solenoids, in spite of testing good on the bench, would overheat and let go after a few minutes running inside the hot cabinet.
I now have a pretty good idea of how a RV furnace works. lol.
Thanks all for the help.
JC
Just in time for summer JC LOL ;D
Glad all is well now JC. Now you can jump in your bus and start hitting the NorthWestern Bus Nuts rallies up there just over the border. Check out our rally page or the NWBN website for the ones they have scheduled so far. http://busconversionsstore.com/rally-news/
Quote from: lostagain on April 21, 2018, 12:17:28 PM
Bingo!
I now have a pretty good idea of how a RV furnace works. lol.
Thanks all for the help.
JC
That's the way it works! by the time I find out everything I need to know about my problem, I have a new problem! ;D >:( ;D >:(
TOM