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Old 11-05-2012, 09:07 AM   #1
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Furnace Ignition Problems, NT-30K

I recently bought an 88 Excella and am having trouble getting the furnace to ignite. When I turn the thermostat on the fan blows but nothing else happens, i.e. no noises, no flame through the window, etc.

The trailer has been idle for some time and everything around the furnace is pretty dusty and dirty. Gas is working fine on the stove and refrigerator.

Any ideas on where to start or a trouble shooting checklist?

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Old 11-05-2012, 09:29 AM   #2
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The sail switch may not be making contact. The sail switch is activated by the air movement of the fan. The fan may not be up to speed or the switch may be out of adjustment or defective.
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Old 11-05-2012, 11:09 AM   #3
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What azflycaster is saying makes sense. The furnace in our '88 Blows cold air for what seems about 2 minutes before the furnace blows out any warm air and conversely once the furnace is turned off continues to blow unheated air for about 2 minutes before the fan stops blowing. The sail switch explanation helped me understand why now.
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Old 11-05-2012, 01:11 PM   #4
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Thanks. Can you tell me where the sail switch is located?

Also, I found a manual that refers to a "manual shut off valve". Is that the valve on the gas line?
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Old 11-05-2012, 02:09 PM   #5
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Thanks. Can you tell me where the sail switch is located?

Also, I found a manual that refers to a "manual shut off valve". Is that the valve on the gas line?
That would be it.
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Old 11-06-2012, 09:33 AM   #6
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So I assume the sail switch is located in the rear of the furnace, and I would need to remove the unit to access it?
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Old 11-06-2012, 11:32 AM   #7
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The sail switch is located at the back of the unit where the fan is. You can check operation by looking for a 12V signal to the control board. If the sail switch does not close no power goes to the control board. When things are working correctly it tries to start 3 times. You usually hear a clunk when the gas solenoid opens and then a tic tic tic noise when the ignitor fires then woosh it starts up if you have gas flow. If it does not start the fan will stay on indefinately till you reset the thermostat.

Perry
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Old 11-06-2012, 01:03 PM   #8
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I may be a little slow here but I have read a bunch of the heater threads and still don't know. How do you get to the sail switch and the control board? Can you get the guts out of the outer shell without disturbing the ducting or do you have to take the whole thing out and disassemble on the bench?

Thanks, Dan
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Old 11-06-2012, 01:05 PM   #9
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The sail switch is located at the back of the unit where the fan is. You can check operation by looking for a 12V signal to the control board. If the sail switch does not close no power goes to the control board. When things are working correctly it tries to start 3 times. You usually hear a clunk when the gas solenoid opens and then a tic tic tic noise when the ignitor fires then woosh it starts up if you have gas flow. If it does not start the fan will stay on indefinately till you reset the thermostat.

Perry
On the newer boards, even the fan will shut down if the furnace does not light. Suburban finally added that feature, which is very welcome to save a battery if the gas runs out or no ignition happens in the three try and out sequence. I am sure the new replacement boards by other companies have the same feature now, again, very welcome.
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Old 11-06-2012, 02:56 PM   #10
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I don't see the control board on that picture. Mine is on the right side. I don't think changing the control board will turn the fan off for you. The fan controls the board on the old units not the other way around. I am sure on the newer units the board controls everything. Yours maybe newer than mine and it may already have that feature.

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Old 11-06-2012, 05:40 PM   #11
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Ours had lots and lots of problems with sail switches. Had it changed out once or twice, then started working on it myself. Basically, what I found was that just removing it, blowing it out with compressed air, and reinstalling it would work, though only for another year.

On the last occasion, I pulled the replacement sail switch out of the (sealed) mailing box that we had ordered a couple of years before and found that the switch itself had been redesigned: The sail was slightly larger and included a slight curve in the sail to form a cup-like shape. In my view, that would probably fix the recurring problem, so rather than cleaning the old one, I installed the new one.

Long story short: The redesigned sail switch is still working.

Oh, an additional point, I guess. I've replaced the sail switches in several RVs here at the park. Believe me, accessing and replacing/repairing the sail switch in the NT is a whole lot easier than doing it on other designs. (Of course, that may merely be a function of having done it so often on ours!)


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Old 11-07-2012, 12:00 PM   #12
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Suburban furnace troubleshooting list:





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Old 11-07-2012, 12:01 PM   #13
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eubank, when you replace the sail switch do remove the whole furnace, or is there a way to do it without removing?
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Old 11-07-2012, 12:13 PM   #14
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You'd need to remove the furnace. Remove the screw (if there is one) from the vent outside. Remove vents and wiring. Remove screws holding the furnace in place. And pull it out.

We had to remove ours so often that I finally included a four-way wiring connector to make future removals as easy as possible.


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