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Old 09-12-2014, 07:06 AM   #1
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1982 31' Airstream 310
champaign , Illinois
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Suburban NT30ma

So I was going through and testing systems on my 310 starting to get ready for the fall rally in northern Illinois and my furnace is acting up. Its the original suburban nt30 ma. It had been running just fine, went through and cleaned what i could earlier this summer without pulling the unit. I had pulled the ignitor and cleaned it a while back and it had been firing just as it should.

So now the blower kicks on, the ignitor sparks, a flame ignites (though it looks like its pretty weak, like it may be a first stage flame before the main burner ignites) then the flame stays on for a few seconds and goes out. So the sequence makes it all the way till the burner should ignite then goes out.

Ive read about this model and realize there was a recall due to the crossover tube and since i havent pulled the furnace yet im not sure if it has the metal or plastic crossover tube.

So my question is, any ideas on next step to troubleshoot? Kinda seems like it may be a flame sensor or control board issue. Poked around on the interweb and couldnt find reference to parts for this model and read somewhere that Suburban no longer supports parts for this model due to its problems.

Should i just save my time, money, and effort on this unit and wait till i can afford to install a new furnace? Do not want to throw good money after bad. I can always use some supplementary electric heat for this fall.

Any sage advice out there?

The kiss of death was when i posted that all systems were mow up and running great! Ill never say that again!

Thanks all,

Mike
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Old 09-12-2014, 01:33 PM   #2
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Pulled the furnace. It does have the metal cross over pipe. Very little rust or corrosion anywhere.
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Old 09-13-2014, 03:53 AM   #3
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I'm not sure which board you need but I have two Dinosaur boards, model UIB S, Rev. 10 if you can use them. They don't fit my furnace.
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Old 09-13-2014, 06:10 AM   #4
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Ill check on their site Dan and see which one it is. I was suprised to see how clean it was when i got it out of the housing. Im gonna try and pull the burner assembly today and make sure its clean and check the orafice. Maybe cycle the gas valve a few times and make sure its working. According to the AS manual, if it fires and then goes in to lockout repeadedly, they recomend checking the orafice and then control board. Thanks for getting back as always.
Mike
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Old 09-13-2014, 08:00 AM   #5
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Looks like the correct replacement for my control board is the UIB-L, large. Thanks for the offer though Dan.

Mike
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Old 09-13-2014, 09:42 AM   #6
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It is also very common for those furnaces with the cast iron burner to have rust in the burner slots causing a week flame and poor combustion. Removal of the burner is not easy, but can be done. A hack saw blade will remove the rust from the slots.

I know you really don't want to hear this, but a 32 year old furnace is just not worth spending much time or money on, especially considering the safety issues involved. It is like playing a combination of whack-a-mole and Russian Roulette. Solve one issue, and another pops up.
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Old 09-13-2014, 10:37 AM   #7
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Im with you on that Idroba. Im gonna take a look at the burner and the orifice this morning, clean up the burner, blow out the combustion chamber, clean the squirrel cage the best i can without removing, clean the contacts to the control board and reinstall. If it ends up needing control board or a gas valve im gonna just bite the bullet on a new unit. It looks like to me that a nt30sp is a direct replacement. I didnt pull the housing out just the inards. Getting the furnace housing out would be a real PITA due to the flooring that was installed by the PO. I think i read some where that the suburban nt30sp will slip right into the housing of the nt30m.

I dont want to throw much $ at this old unit, like you said, so ill be replacing it unless its a simple inexpensive fix.
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Old 09-13-2014, 10:59 AM   #8
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The original furnace in my '82 was an NT30. I know my dad repaired it multiple times with new circuit boards, etc. I nursed it along myself for about 4 years. Last thing I did to it was to change the electrode and I replaced the original regulator on the propane tank to ensure all appliances were getting an adequate supply of propane...I didn't have a gauge to test, but I could smell a little propane at the regulator, so it was time to change it anyway.

I thought all was good, but just as winter was approaching a year back, the furnace started to constantly go into lockout mode where the burner shuts off and the blower stays on until I turn off the furnace with the thermostat. Waking up in the middle of the night with cold air blowing from the furnace is not fun

I decided not to mess with a 30 year old furnace any longer and I replaced it with a new NT34. I also ran new ducting front and rear. That was a big job to do in the rear but well worth the effort. I used flexible ducting that had insulation around it. I did my best to straighten out the ducting going to the rear as much as possible to get the best flow I could.

The new furnace is awesome! I can't believe how well it works and just how much hot air it puts out. Actually it is putting too much hot air out in the front...I sort of need dampers in the ducting up front now.

If I had to do it again, I wouldn't hesitate replacing the furnace with a new one.
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Old 09-13-2014, 11:09 AM   #9
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When I replaced the NT furnace in my 310, I put a smaller one in, 24,000 btuh. It had a lower amp draw which was good. Plenty of heat too at least in any temps I wished to go camping in.

I also added ducts, the original furnace was under supplied with output vents. I added a new one in the front, and it made a lot of difference in how the unit preformed.
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Old 09-13-2014, 12:55 PM   #10
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Well i pulled the burner and all but about 4 slots were rusted nearly completely shut. Used your idea Idroba and ran a hacksaw through them, cleaned it all up with a wire wheel. I blew out the combustion chamber the best i could with an extension on my air hose. Eh.......I'll put it back in and see how it does. Looks like i will be buying a furnace at some point in the near future.
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