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Have a '98 winnebago 33WB with a suburban furnace model sf-42. Have followec the
book instructions. System will no ignite. Only blows cool air.
Any suggestions?
The suburban is notorious for not firing. There can be several very good reasons, and there can be no apparent reason at all.
To start with check voltage while it is trying to start, Low voltage will not work. You should be able to hear the spark igniter clicking. But to explain the basic operation. The blower actually has two blower wheels. The circulation inside blower, and the induction/combustion blower. There is a sail switch that turns on power when the blower get up to speed. Then a time delay starts, 15 sec or so, and power goes to the igniter, and the double valve.
I would probably just pull it out, by removing the screw from the exhaust on the out side, the inside, you can pull the furnace out of the case, or pull it all out, The ducts are usually attached with twist lock fittings.
If you want to just pull the furnace without the case, the duct removal is not necessary, but it is often times necessary in order to raise it up some to get it to clear the front of the space it is installed in. You will probably have to disconnect the electrical connection,3 wire plug. And the gas line. After you pull the furnace out, pull the electrical lead out so it will plug back into the unit. Locate the sail switch, and check it with an ohmmeter to see if it is working by hand. Dirt dobbers are the most trouble in our part of the country. I would pull the ingiter plate and check and clean the system. You can also fire it up and watch the points fire, just clamp them to the metal so it does not shock you. Good way to adjust the fire gap.
If this works that means your board is working, and you are getting power to the igniter, and most likely to the valve, I would reinstall the ignition system. Now, have some one turn the stat on, and blow on the gas pipe. You should feel it release when the igniter starts. If you think the igniter was the problem, or dobber nest, and your think it is solved, re install it and try it. If have not found any thing that you think was a problem, pull the burner jet. Not easy to get too, but can misdirect, or restrict gas flow. Little spiders can actually build in the orifice. Or a dobber can do basically the same.
If it does not fire after the time lapse after the close of the sail sw, you can suspect the board. Check for loose connection, if not obvious, is it probably bad if you have sufficient voltage, good ground etc.
It the igniter fires, and the valve opens, it is either a restriction within the orifice, burner inlet, or it can be gas pressure. Gas pressure at the manifold should be 10.5 to 11 water column inches. If you are not familiar with checking procedures, get a professional to do it for you.
That is pretty much it. The most annoying problem with these units is intermittent. Which means it will only fail on the coldest night. Suspect low voltage if it is on a battery alone. Suspect gas pressure if the dc voltage is sufficient. If neither, it is the board or a loose connection.
Mallie
I have an old suburban furnace in my rv, aprox.1983 30,ooo btu. When I try
to fire furnace the igniter starts clicking, the burner flames up for aprox. 20 seconds then flame goes out,
igniter automaticly starts firing again, however only hear popping noise, sounds like its trying to lite, however burner never comes on and stays on.
Have any tips that might help me.
THANKS!
I just bought a cargo trailer made
by us cargo. I have been trying for
three days to get my Suburban furnace to ignite. I've checked batteries and voltage- good, I've ran all other appliances on gas they work good,
the blower motor kicks on when you turn the furnace on and I can hear the igintion trying to ignite three times
before it stops trying to lite -
goes to lock out I assume.Is this a
possible bad sail swith-paddle swtich
in a brand new furnace? And of all the
manuals that this coach has the one and only one I'm missing the ( Suburban Furnace) manual! Please help!
I have a defective "high limit" switch in my six month old Suburban furnace. How much (labor) time should it take a qualified technician to replace this switch?
email Don tabler
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