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Old 10-28-2012, 06:29 PM   #1
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Suburban furnace model NT-12S

I am living in Flagstaff AZ (7000 ft) and have been going up to Colorado to higher elevations and have been experiencing problems with my Suburban furnace. The furnace is failing to ignite. It makes 3 attempts to ignite but does not. I have found that by placing my hand near over the exhaust/intake port during the attempted igniting, the unit will fire. I have followed recommendations from various forums to remove the unit and clean/remove any dedris from the combustion chamber but this has not resolved the issue. I have also replaced the ignitor and control module board as well with no result. The last thing I was told that maybe air/fuel issue. Would appreciate any input.

Thanks!!!!!!!!!!!!!!!!!!
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Old 10-28-2012, 08:23 PM   #2
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Re: Suburban furnace model NT-12S

I've been working on the same issue. Here is a thread with suggestions http://sportsmobileforum.com/viewtopic.php?f=40&t=9800. I found a lot of air in my tank when I vented it. It ran open for almost two minutes until I could smell propane.. Hope this helps
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Old 10-29-2012, 09:39 AM   #3
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Re: Suburban furnace model NT-12S

Another thing outside of the air purge, would be to start the van to get the voltage up. The blower motor RPM is directly proportional to the voltage. Lower voltages may not produce enough air flow to close the sail switch. This problem also increases as you go up in altitude because of density of the air. Holding your hand if front of the intake/exhaust may give it a boost as you remove it which may get the sail switch to close. Any obstructions in either the blower van inside for heat, or to the burner intake/exhaust can reduce the performance as they run off of the same motor.

-greg
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Old 10-29-2012, 08:54 PM   #4
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Re: Suburban furnace model NT-12S

This is all good information! I'll try running the vehicle to see if this makes any differents. I was also going to take the van into a local RV repair shop to see if its delivering the proper amount of fuel to the furnace, by checking the regulator. If these checks fail, does anybody know of a better designed furnace that works at in all type of environments/elevations.

Thanks!
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Old 10-29-2012, 09:49 PM   #5
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Re: Suburban furnace model NT-12S

I found this thread helpful. viewtopic.php?t=1858&start=0

My issue turned out to be an air flow problem. I had a lot of road dust in and around the furnace. It fired right up after a good blow out with compressed air. I think we chatted at the USGS about your furnace a while back?
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Old 10-30-2012, 10:16 AM   #6
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Re: Suburban furnace model NT-12S

Battery voltage would be my first suspect if the furance is clean. I suppose the fan motor could slow down if it was old too. Years ago I tweaked the sail switch on my Suburban to help it start reliably. One day I was standing near the exhaust when it tried to fire up and it backfired. Probably shouldn't modify the sail switch...
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Old 10-30-2012, 10:29 PM   #7
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Re: Suburban furnace model NT-12S

Hey Joe,

Thanks for the thread, I did try running the vehicle for awhile to see if I could get the furnace blower to spin up faster, I still couldn't get the furnace to fire. So, again after blowing out the conbustion chamber and replacing the board "control module/ignitor it looking like a trip to the RV shop. Any other suggestion on a better design furnace would be appreciated.

Thanks again all..............

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Old 10-31-2012, 04:52 PM   #8
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Re: Suburban furnace model NT-12S

Our Propex has a variable speed motor and it will supposedly operate with a fairly wide range of voltage. It actually runs the fan at high speed during purge and ignition, then slows down to the operating speed. It also claims to draw less current than a similar Suburban. We selected it for lower power and gas consumption and lower noise. And hopefully more reliable operation.

One other thing I did on our old Suburban was to adjust the gap from the igniter to the ground to try to get a stronger spark. (needle nose pliers)
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Old 10-31-2012, 09:58 PM   #9
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Re: Suburban furnace model NT-12S

dhally,

Which model Propex are you using and does it seem to operate at various elevations? Got the van back today from the RV shop and still not able reslove the issue. According to the repair tech, he also thinks it is an air flow issue and wants to tear down the furnace to see what could be causing the problem @ $120 per hr. I've given up hope and feel the next step is to replace the furnace. Any other recommended replacement furnaces would be apperciated.

PS: Service tech also checked regulator on the LP tank and found the water column/PSI reading to be within required specs.

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Old 11-12-2012, 07:48 PM   #10
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Re: Suburban furnace model NT-12S

So, here's the latest for those of you that may be interested. I spent this weekend in McDowell Mountain Park with the wife and our dog and found that that furance performed like it should at an elevation of around 1,500 ft. It dropped down to around 40and usually fired up on the first to second attempt. Today we drove up to Prescott (elevation 5,000 ft)and it fired up there on the third attemt on the first cycle. Just got back to Flagstaff (elevation 7,000 ft) and nothing! Can't get it to fire. So, after spending several days researching and replacing parts, the conclusion I've come to is that the Suburban NT-12 doesn't operate properly above 7,000 feet. If anyone out there knows of a solution to get this thing to fire at this elevation short of placing your hand over the intake port outside the vehicle during its ignition stage, I would love to hear it.

Thanks all!
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