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Old 09-14-2004, 09:07 PM   #1
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Furnace problem

I have an 87 Sovereign with a Suburban furnace. This past weekend, when I clicked the furnace on, the fan came on but the furnace didn't light. Nothin but cold air.

What should I check first? Is this a common problem?
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Old 09-14-2004, 10:03 PM   #2
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Quote:
Originally Posted by bbrackman
I have an 87 Sovereign with a Suburban furnace. This past weekend, when I clicked the furnace on, the fan came on but the furnace didn't light. Nothin but cold air.

What should I check first? Is this a common problem?
My 87 Sovereign had a bad gas control valve when I bought it. It was an intermittent problem at first(2-3 times it was used) but, then it just quit. The furnace was removed and bench checked. I think you would have to remove the furnace and hook it to 12 volt + a thermostat to check the valve to see if it is opening.

It cost about 50% of a new furnace to repair it. $175 parts + $75 labor.
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Old 09-15-2004, 08:37 AM   #3
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There is some information in the archives on troubleshooting these furnaces. The problems that come quickly to mind are a bad ignitor, dirty burners, bad thermocouple, bad sail switch, bad gas valve, insufficient voltage, insufficiant gas pressure, and, of course, a bad circuit board.

The problem is that the furnace has to be removed to be bench tested, and almost any repair is likely to be $100-$200 plus. This may be hard to justify in a 18 year old furnace.

Mark
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Old 09-15-2004, 09:44 AM   #4
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Were you plugged in when this happened? The furnace needs enough 12V power for the fan to move the "sail switch" out of the way. If your batteries are low then the fan will blow air but not have enought fource to trip the sail switch.
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Old 09-15-2004, 04:18 PM   #5
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furnace

We had the same thing happen on our 76 last year, take the cover off and take a soft brush like brass and clean around the pilot and that area, blow it out if you have a small air compressor. That is what we did and it has worked all last fall. Marvin and Annie
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Old 09-22-2004, 10:18 PM   #6
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My problem was the limit switch. Only cost $8.00 for a new switch and she's good as new.

Thanks for the help.
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Old 09-22-2004, 10:25 PM   #7
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Quote:
Originally Posted by bbrackman
My problem was the limit switch. Only cost $8.00 for a new switch and she's good as new.

Thanks for the help.
Isn't it nice when a fix is less than $10.- !!
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Old 09-23-2004, 07:30 PM   #8
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is the gas on?

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Old 12-23-2004, 01:00 PM   #9
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so how did you know it was the limit switch? Also any tips on pulling the furnace out?
I disconnected the gas line, and unscrewed the one screw in the front (inside the door) and screws on the vent outside, it did not move. I must be missing something holding it in.
It will light sometimes and burn but not a blue flame, more orange-yellow. On my last trip it lit for awhile, then would not light at all, and made that banging sound when it did light. We shut it down and used the roof heat strip.
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Old 12-23-2004, 02:57 PM   #10
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Blower goes on - means thermostat and time delay relay are OK.

No ignition: this is a DSI (direct spark ignition) furnace, right? No little cap with a window to use to light a pilot?

First, make sure you have adequate gas - usually a burner on the stove will give you a pretty good idea of this is the case, but do check for the shutoff valve underneath trailer on the line going through the floor.

Then check to make sure that the ignitor and flame sensor have an eighth inch gap (some furnaces don't have a separate flame sensor but those that do need to have that electrode farther from the spark source than the ground.)

Then check the limit and sail switches - this usually means pulling the furnace out. They are wired in series with the controller board and you can use a 'bench test' to see if they allow the voltage through them when the fan is on by thermostat. (these safety switches are $10 to $20 items)

Then check the gas valve solenoid voltage. It should be energized when the controller board thinks it is time for gas. Look for spark between the ignition and ground electrodes. (the gas valve runs $100 or so)

If the controller board is getting electricity through the limit and sail switches but you don't get any spark or gas valve energy, then maybe the controller board is kaput ($100 or so).

As always, keep in mind that LP or propane is nothing to play around with. Know what you are doing, take appropriate precautions, and don't take any chances.

see http://marksrv.com/suburbanparts.htm for an idea about parts and costs.
his trouble shooting guide isn't bad, either
http://marksrv.com/furnace_trouble_shooting.htm
another good one is at
http://www.rverscorner.com/articles/furnace1.html

The guts of the furnace are held in by a couple of 'shipping screws' usually to the floor of the casing and by a long screw that comes in from the middle of one of the outside vents. Also the electrical plug and the gas line and manifold need to be disconnected so the guts can be pulled out of the front of the case.

Also, do check for obstructions in the vents and make sure you get good airflow through the combustion chamber. Sometimes insects like to make nests in the vent tubes.
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Old 12-23-2004, 04:42 PM   #11
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Quote:
Originally Posted by ALANSD
...but not a blue flame, more orange-yellow. On my last trip it lit for awhile, then would not light at all, and made that banging sound when it did light...
That type of flame means it is burning too rich. Sounds like Andy nailed it in this thread.

You may want to check the air adjustment screw before pulling the entire unit out.

Tom
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Old 12-23-2004, 06:52 PM   #12
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thanks- but I have already adjusted it for all the screw will do. I figure the lack of use and dirt must be the problem.
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Old 12-23-2004, 09:43 PM   #13
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a yellow flame indicates that there is not enough primary air being mixed i dont know if there is an air adjustment shutter on yours, but dirt or insects are likely suspects. occasional yellow in the flame indicates impurities.
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Old 12-23-2004, 10:21 PM   #14
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Unhappy probably plugged up

Mine did that when I got it - turned out the burner box was badly plugged up with soot. Apparently the screen on the outside of the air inlet gets plugged first, so it starves for air, then it starts to burn rich (yellow flame), then it becomes poisonous. Mine gave me headaches and set off a CO alarm I bought for safety. I was enroute back to the west coast from Wisconsin and was freezing cold at night.

A guy at an RV repair facility in Missoula used a wand on an air hose to blow it out from the outside and inside (behind the small screw on cap) for about 15 min, while banging on it, until the soot was all gone. Worked great after that and still does, but Andy said that was a no-no due to the risk of cracking the burner box, so I suppose it has to come out for cleaning. It was amazing how much junk was in there.

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