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Old 01-06-2009, 06:03 PM   #1
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More fun with the 'burb.

Here's a good one. My Suburban furnace only works when it's 30 degrees F or over. Below 30, it runs the fan, fires the spark but won't run. I just had the tank filled and ran through the purging procedure--bled it for 20 minutes. Nothing but LP smell came out of the bleeder valve--seemed like a strong LP smell. Should a visible vapor, or liquid, come out of the bleeder?

Thanks
Tom
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Old 01-06-2009, 06:55 PM   #2
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hmm... I've never had a strong smell. Something sounds wrong with that unit. Also, i've lit ours in 20 degree temps before.
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Old 01-06-2009, 07:38 PM   #3
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Quote:
Originally Posted by adventureduo
hmm... I've never had a strong smell. Something sounds wrong with that unit. Also, i've lit ours in 20 degree temps before.
I was referring to the smell when I was trying to purge the LP system. It's not from the furnace. John told us to bleed the tank until we get a strong LP smell.

Tom
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Old 01-06-2009, 07:45 PM   #4
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Gotcha, read to fast. I've only bled mine when being filled and that was for a few seconds with propane guy filling it at the same time. There was white that came out... just like a tank for a BBQ grill. I don't know what it's supposed to look like after you get it home and try it. It may have been white and strong odor because i was pumping at the same time.
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Old 01-07-2009, 02:27 AM   #5
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furnace

Tom,

Since the ignitor is working, the problem is most likely a lack of LP Gas to the burner. Several things can cause this. Confirm the main LP Gas valve is "on". Confirm that the house battery voltage is adequate to spin the furnace fan fast enough to engage the sail switch. Easiest way would be to start the van and see if the furnace lites when the van engine is running (provided the alternator is charging the house battery).

If the furnace doesn't operate when the van engine is running, restart the furnace and check that you get an LP Gas odor at the exterior furnace vent. You should be able to smell LP Gas once you hear the ignitor at the exterior vent. If you don't smell LP Gas at the exterior vent, check for any type of blockage for the interior air return. Sometimes blankets or sleeping bags cover the air return and prevent the furnace sail switch from making contact, which will not allow the LP Gas solenoid valve on the furnace to open (I know that the ignitor shouldn't operate if the sail switch makes contact, but sometimes it does, maybe just not as long). I've seen an accumulation of dust in the exterior vents cause problems too.

If you do smell LP Gas at the exterior furnace vent, then it's possible that the burner needs to be cleaned. It tends to get rusty and can prevent LP Gas from getting close enough to the ignitor. Follow Suburban's instructions on removing and re-installing the burner. You can get more in-depth troubleshooting for your NT-12S or NT-12SE furnace at; http://www.appliedgmc.com/instructions/ ... urnace.pdf


I hope this helps.

John K.
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Old 01-07-2009, 09:57 AM   #6
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Re: furnace

Quote:
Originally Posted by John Kalmbach
Confirm the main LP Gas valve is "on".
It takes several turns, mine it tight at close and open but spins pretty freely in the middle. Make sure you open it until there is resistance, but don't force it past there.

Quote:
Easiest way would be to start the van and see if the furnace lites when the van engine is running (provided the alternator is charging the house battery).
Shore power should provide power directly to the house batteries, so you don't have to wait until the van batteries top off.


Quote:
Originally Posted by neeemo
I was referring to the smell when I was trying to purge the LP system. It's not from the furnace. John told us to bleed the tank until we get a strong LP smell.
On filling, your propane dealer (I can hear Hank Hill: Pro-pain and pro-pain related accessories) should know the correct method. Unfortunately every one's idea of correct is different.

The gauge on your SMB has red for about the 1st quarter and for the last.

You should never let it get to zero (through the red) because a dealer might insist that indicates a leak and refuse to fill without a complete leak test on the system.

The upper red is for expansion pressure- you fill in winter to 3/4 and it gets warm, the last 1/4 is for that expansion.

When filling the attendant opens the bleeder valve. It is possible to fill until liquid propane comes out the bleeder, and I've had a few that think this is the correct procedure. SMB and my friendly local RV shop say stop at smell, which is the indicator you're about to get liquid.

Either way gets you to about 3/4 of a tank. I imagine if you keep going once liquid is pouring out you can go over, but otherwise I haven't seen problems from the fills.

Once the bleeder is closed and the pump is off, the line is still pressurized. On all the fill systems I've seen there is a back pressure line- usually a rubber tube going back along the hose and loose on the ground. The attendant should release the pressure in the line and you get strong propane smell as it dissipates a few feet away. If they don't, when they pull the pressurized line, you get an unwelcome burst of propane into the van chassis. Let me tell you, even with a fantastic fan this is a drag to get rid of (although not as bad as diesel).

As long as your gauge is above the lower red you should have sufficient propane in the tank to run the furnace.
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Old 01-08-2009, 10:43 AM   #7
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Neemo, Did it fire with the engine running?? I had a similar issue back in the fall and it was directly related to battery charge. If I started the van or had shore power the furnace worked fine. My batteries were 4 years old and when it was cold, especially at higher elevations, the batteries would not spin the fan enough. oclv
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