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Old 11-28-2006, 09:49 AM   #1
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furnace starts and stops

I have a 1977 AS with a suburban furnace(by the way just purchased the AS).Before I started the furnace I thought it would be a good idea to remove furnace and disasemble to make sure it was clean.Sure enough it was very dirty and the fan was full of paper like nest for something.Hooked up power on bench and every thing seemed ok. Installed back in trailer and turned thermostate up and fan came on few seconds then ignition and furnace lit for about 30 seconds and fire went out ,tried turning thermastate up and down but fan would not start. The only way fan would start again is if I disconnect gas line going to furnace.Sure would appreciate any help. Thanks
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Old 11-28-2006, 09:41 PM   #2
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Hi Binder,
I see you are a newer member - Welcome!

Frankly, I don't know what may be causing your problem.

My posting will bounce this to the top of the list again, hopefully someone can give you an answer.

Also, I know there was a recent thread with the same or similar question. If you haven't already done so, search for previous posts on heater problems. Good luck!
Dave
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Old 12-31-2006, 08:49 PM   #3
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Question NT22A Blues

I have a similar problem. I am working on a 71 Tradewind. The PO told me his father took out the furnace to use it somewhere else, never did, and never put it back. The furnace shows signs of very little use, as does the rest of the coach. The coach has been sitting for many years and was a mouse condo.

I put the furnace in and I guess I wired it right because the blower blows, pilot lights and main burner lights. The main burner only stays on for about a minute and then the pilot is out also. I think it is probably a good idea to blow out and brush off whateve I can get to from the pilot access. Hopefully I don't have to pull this sucker out again.

Also the little sparky thingy worked great for a while and now does not spark.

Any suggestions from Airstream Land?

Marshall
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Old 12-31-2006, 09:13 PM   #4
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We have a similar problem with our furnace on our 85 Soverign. When we turn on the thermostat the fan will come on first and sometimes the furnace fires/lights. It comes up to temp and goes off, then when it comes on again it doesn't light - no warm air - just the fan and cold air....
It worked fine when we got our trailer except for a squeaky fan - had it serviced at an Oregon dealer in the Willamette Valley - they fixed the squeak but now it's hit and miss on the heat! AAARRRRGGGG
Been using a portable electric heater........
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Old 12-31-2006, 09:15 PM   #5
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I posted a reply earlier today in reference to a cold weather and a problem in Northern Vermont with LP Gas furnace. Hope it helps http://www.airforums.com/forum...-vt-28961.html

GAS PRESSURE
A furnace is a consumer's friend when the outside temperature gets colder. Unfortunately though, cold is an enemy of LP gas. The BTU capacity of LP per volume decreases as the outside temperature gets colder. Therefore, based on how full the LP tanks are, the ambient temperature outside and how many BTU's the furnace is, there may not be enough gas to sustain ignition on the furnace.
One's first thought might be that the burner or valve is bad. However, the vaporization capacity of the tank in these conditions is lower than the furnace BTU rating. The furnace is not going to perform very well because there is insufficient BTU capacity in the tank.
If you were to put an insulated fire resistant blanket over the tanks and a 75 watt light bulb under that, you would probably raise the temperature of the bottles 10-20 degrees and almost double the BTU capacity of the tank. This in turn would allow the furnace to operate properly. So keep in mind that a furnace problem is not always a component problem.
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Old 12-31-2006, 09:27 PM   #6
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BINDER,
I had the same problem and the local RV repair guy found the combustion chamber full of mud dauber nests, the electric motor was on the down side and was just spooling up fast enough in the beginning to trip the sail to open the gas line. The board also was bad and that was not letting the furnace ignite after the first time. After the chamber was cleaned out, new motor installed, new board put in, it worked like new for a weekend. It then started acting up again, sometimes failing to ignite after the first time. I took the trailer back and the guy found that a limiter switch which limits the temp was bad and it had messed up the board again. He ate the board, replaced the limiter as well as the board and I was good to go. If I had known I would be paying $384 to do all this, I would have ordered a new furnace and put it in myself.
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Old 12-31-2006, 09:40 PM   #7
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NT22A Blues/ more

To add to my earlier post. When the burner and pilot go out the blower keeps running until I turn it off at the thermostat. The furnace does not get up to temperature.
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Old 12-31-2006, 09:43 PM   #8
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check for traces of spider webs/nests in the burner mixing tube and chamber. they love the smell in propane.
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Old 01-01-2007, 07:21 PM   #9
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JStanley,
I think you may be on to something. Just got back from a four-night trip where temperatures ranged from in the 40's the first day or so, and then in the high 20's last couple of nights. Furnace seemed to work fine the first three nights, and then got to where the blower would run and blow cold air only on the 4th night (when it was the coldest). I thought my bottle was empty but it was still in the green. Switched to the other tank anyway, which was full, and everything seemed to work OK again. Although the one bottle apparently wasn't empty, it had to be pretty low as we had used it pretty heavily for three days. Believe I will try your suggestion with a wrap on our next winter voyage. Thanks
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Old 01-01-2007, 08:06 PM   #10
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Quote:
Originally Posted by Marshall
To add to my earlier post. When the burner and pilot go out the blower keeps running until I turn it off at the thermostat. The furnace does not get up to temperature.
Is your trailer doing this when on shore power or when off the grid? It could be the same problem I had with a motor that kept running a little slow when off the grid even though I had brand new fully charged batteries. It could also be a board problem. For what its worth, newer boards can be purchased which will stop the motor from running if the unit fails to ignite.
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Old 01-01-2007, 08:14 PM   #11
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Quote:
Originally Posted by davidz71
Is your trailer doing this when on shore power or when off the grid? It could be the same problem I had with a motor that kept running a little slow when off the grid even though I had brand new fully charged batteries. It could also be a board problem. For what its worth, newer boards can be purchased which will stop the motor from running if the unit fails to ignite.
Shore power, I have a car battery in the trailer temporarily but I have not yet tried to run the furnace just on the battery.

Does a 1971 NT22a furnace even have a board?
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Old 01-01-2007, 09:32 PM   #12
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Quote:
Originally Posted by Marshall
When the burner and pilot go out the blower keeps running until I turn it off at the thermostat. The furnace does not get up to temperature.
If the pilot dies and the thermocouple goes cold, the gas will automatically shut off. The furnace fan will continue to run automatically to vent any accumulated gas for a predetermined amount of time. Sometimes the firing of the furnace can kill a weak pilot...then the furnace will not start the next time heat is called for because the gas has correctly shut off at the regulator. I had this happen as well as other unmendable problems and threw the 30 year old piece-o-junk boat anchor out. I am saving up for a new one...

Best of luck,

Steve
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Old 01-02-2007, 08:15 PM   #13
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one of life's lesser mysteries

Quote:
Originally Posted by sfixx
If the pilot dies and the thermocouple goes cold, the gas will automatically shut off. The furnace fan will continue to run automatically to vent any accumulated gas for a predetermined amount of time. Sometimes the firing of the furnace can kill a weak pilot...then the furnace will not start the next time heat is called for because the gas has correctly shut off at the regulator. I had this happen as well as other unmendable problems and threw the 30 year old piece-o-junk boat anchor out. I am saving up for a new one...

Best of luck,

Steve
I'm not quite ready to deep six it, actually having some fun tinkering. By the way most people are surprised by the number of boats in New Mexico.

As suggested, there does seem to be a relationship to the air temperature and operation. It has been quite cold here for NM ,overnights about 0 degrees and I was not able to keep the pilot lit for more than a minute or 2. It warmed up today and the pilot stayed on for an hour or so, until I turned on the thermostat and the main burner fired up. The main fired for a minute or so, THEN I HEARD A DISTINCT CLICK I didn't notice before and the burner and pilot were both out. The fan kept running until I shut it off with the thermostat 5 minutes later. I will try it again when it warms up outside a little more. Also, there is a DISTINCT SMELL that I don't think should be there when the burner fires and the furnace is warming up. Maybe it is just that this furnace has not been used for many years, or, COULD IT BE SOME KIND OF BREAK DOWN IN THE COMBUSTION CHAMBER SEAL from the heat exchanger?
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Old 01-02-2007, 08:42 PM   #14
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Maybe RV Lew will chime in here, but there's a lock out switch that will shut off the gas if the temperature rise is too fast in the heater. This can caused by inadequate ducting of the heated air. The thermocouple will also sense an absent flame and turn the gas off. I think, but I'm not sure, that the board-equipped heaters turn on the spark before the gas turns on. Without the sparks, I doubt the board would LET the gas come on. Thus problems can occur with the lock-out switch (fan keeps running), the ignitor board (fan keeps running), and the gas switch itself (spark but no ignition and the fan keeps running). On the three heaters I've had, there's been a little circular window over the overheat switch. I don't know what it looks like if it activates.

My guess is that Binder should check his fuel supply, fuel pressure (11 inches of water), and then his gas switch. Oh, after a failed start, you should shut off the gas and run the fan for a while to clear the combustion chamber.

The NT-24 in my Argosy's favorite trick was to put out nice heat until I went to bed, and then flame out during the night. I''ve awakened more than once to a cold trailer with the fan blowing.

The board-equipped heaters can do it too.

Good luck with these things, guys.

Lamar
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