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Old 08-25-2017, 05:37 AM   #1
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1978 31' Excella 500
Reidsville , North Carolina
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Furnace Troubleshooting

I've got a '78 AS Excella with a asuburban heater. When I turn the thermostat up the fan turns on, but the unit never ignites. I've tried starting the unit about 4 times in a row this morning with no luck. The gas is on and the batteries have a good charge.

What steps should I take to troubleshoot this problem?
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Old 08-25-2017, 06:53 AM   #2
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Good article

http://wbcci.org/component/jdownload...rv-iii-propane
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Old 08-25-2017, 01:02 PM   #3
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2014 20' Flying Cloud
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Does your furnace have a pilot light, or a Piezo-style igniter? Can you see or hear the combustion chamber from either the outside or inside of the AS? Please describe anything you hear or see during the failed lighting sequence.

Do your other propane appliances work right, such as the water heater and stove cooktop burners?

If I had to guess, I would consider two possible causes:

-- a sail switch which has gone bad
-- the mother board is shot

To diagnose these two possibilities, you would have to know some HVAC diagnostics information and have the right meters etc.. I would call an RV HVAC service or take the AS in.

We had both things happen in our old 1988 25' AS. If you search above in the blue-bordered Google-powered search box, for those terms, you will find other threads which might be helpful.

Good luck!

Peter
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Old 08-25-2017, 09:43 PM   #4
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To the best of my knowledge 1978 suburbans were not pilotless ignition. They have a pilot light much like most of your home gas water heaters. You need to light it.
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Old 08-27-2017, 12:22 PM   #5
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1978 31' Excella 500
Reidsville , North Carolina
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Sorry for the delayed response. We were camping this weekend with spotty cell coverage.

I'm not sure if the furnace has a pilot or not. I've looked inside the access panel and doesn't seem to be a way to manually light pilot.

The instructions say run the fan for 5 minutes without gas, then turn furnace off, turn gas on and run furnace. If this doesn't work then repeat. I've don't if about 5 times in a row. I haven't heard anything other than the fan running.
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Old 08-27-2017, 01:21 PM   #6
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Quote:
Originally Posted by bombard16 View Post
Sorry for the delayed response. We were camping this weekend with spotty cell coverage.

I'm not sure if the furnace has a pilot or not. I've looked inside the access panel and doesn't seem to be a way to manually light pilot.

The instructions say run the fan for 5 minutes without gas, then turn furnace off, turn gas on and run furnace. If this doesn't work then repeat. I've don't if about 5 times in a row. I haven't heard anything other than the fan running.
What do the instructions say about a pilot light, or Piezo-type igniter? Is there a separate booklet for the furnace? If you have a pilot light, most mfg. manuals will have very clear instructions with photos for how to light the pilot light. You should hear a Piezo igniter's sparking sound if it is working right.

You might just have a loose connection. I would check all electrical connections in the furnace's mechanical space. There are probably a bunch of spade type terminals which you can pull off and put back [carefully by not pulling on just the wire]. Check each spade, when exposed, to make sure there is no corrosion. With a unit as old as yours, you should trace all the wiring and make sure that there are no spots worn off, or signs of corrosion where crimps attach to the wire. If your trailer has been near salt water in NC, corrosion could be an issue, and hard to find, as it is often hidden inside the wires. You might have enough juice to power the fan, but the furnaces "brain" will not let it ignite if the voltage is too low, due to internal corrosion or low batteries.

Are your batteries fully charged? What is the voltage on your monitor panel? Please review Post #3 also for other possibilities.

Good luck!

Peter
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Old 10-07-2017, 12:09 PM   #7
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1978 31' Excella 500
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Update

I finally had time to do some trouble shooting. Still no heat but I have determined the sail switch works and that there is spark in the heater. I can see the igniter trying to light through the peep hole. But nothing ever ignites.

Does this igniter light a pilot light or the burner?
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Old 10-07-2017, 01:09 PM   #8
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AFAIK, if you have an igniter there is no pilot. Before the igniter starts you should hear a click as the control board turns on the gas. You may not be able to hear it because of the fan. Put something (a screwdriver for example) on the gas valve and press the other end to your ear to conduct the sound directly.

You should also be able to measure 12V at the gas valve.

If you don't have 12V the control board may be bad. If you have 12V on the valve and no gas, the valve may be bad. Check to make sure the ground wire is making a good connection to the trailer body.

Some trailers have a gas shutoff valve for each appliance. Unless this worked before and you haven't changed the valve or no one else has, follow the gas line to see if you have one and make sure it is turned on.



Al
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