| [GMCnet] Suburban furnace not starting, [message #339338] |
Wed, 05 December 2018 19:31  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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I checked the thermostat, and related 2 wires. OK. Have good 12 V power. Ground good. First thought was that the control board was the problem. But. I believe that the thermostat turns on a relay. That then turns on the 12 V powers the control board. So I'm thinking that I need to send money to Jim at Applied. Jim will get me the correct part as usual. You SPARKIES think I got it correct? Bob Dunahugh
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| Re: [GMCnet] Suburban furnace not starting, [message #339342 is a reply to message #339338] |
Wed, 05 December 2018 21:12  |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
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Bob, try to jumper out the sail switch. They are a problem lots of times. It might be you're not getting enough air flow to trip it or just a bad/dirty switch.
Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
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| Re: [GMCnet] Suburban furnace not starting, [message #339348 is a reply to message #339338] |
Thu, 06 December 2018 07:24 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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If you have the original 'stat, connect the two wires together and see if it starts. Mine had corroded contacts and didn't close the circuit. If the fan in the furnace come on but it never lights, Hal's cure gets about 80 percent of them. My (limited) experience is low air flow keeps the switch from closing more often than a switch failure.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Suburban furnace not starting, [message #339351 is a reply to message #339349] |
Thu, 06 December 2018 10:52 |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Senior Member |
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More specifically, Is the blower running but no heat or ignition? Or is the blower not running at all? Assuming this is an NT30.
In my Royale, and in no particular order. If the blower is running and no heat, Do you have gas running all the way to the furnace? If my gas has been turned off while driving, I need to call for heat a few times, before it will light. Same with the stove etc. It takes a few tries for the gas to get all they way to the furnace. Next. Do you have the shut off valve open just before the furnace it self? Just checking. Mine is right next to the entrance to the furnace itself, but yours may vary. Perhaps that got shut off accidentally as I know from experience.
Next, if the blower is running can you see if its sparking through the sight window on the furnace. May be a two person job, but when you take the front cover off the furnace, the sight glass is there down low. You have to call for heat and quickly run up and see if you have some blue sparks trying to light the burner. Its hard for one person to do that fast enough and the sparks are not like a spark plug which are easy to see. But no sparks there would help narrow down the issue. When I was replacing the sight glass gasket I pulled the flame sensing electrode and ignitor and cleaned it very gently with a bit with either 0000 steel wool or a dollar bill the way you would with a piece of sandpaper (cant remember which one), but that helped the ignition as well. Similar to a house furnace over time that electrode can get buildup on it. Be careful not to touch it with your bare skin as the oils on your hands are not good for it.
I think I also pulled the sail switch and blew some compressed air through what I could. may not have done much, but I was already in there with the furnace on the work bench.
Lastly, I made sure I had a fully charged battery, or was plugged in and on shore power. If the sail switch is sticky or not getting enough air passing through it, the furnace wont light.
Hope this helps.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: [GMCnet] Suburban furnace not starting, [message #339352 is a reply to message #339338] |
Thu, 06 December 2018 11:17 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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Don't rule out the gas valve mine would stick shut in cold temperatures but worked fine when it was warmer. Had to put a voltmeter on it to find it.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Suburban furnace not starting, [message #339353 is a reply to message #339338] |
Thu, 06 December 2018 11:22 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Mine took several tries the first time I needed it. Problem turned out to be no propane in the lines. Now, when I park and turn the gas on at the tank, I light the stove (it uses a hand held sparker) and keep sparking till the gas gets up top it and it lights... this takes 20 seconds to a minute to fill the pipes. Once there's gas to the stove, the furnace fires off. If the line has to fill, it will fault and lock out before it gets the burner lit. Turn it off and back on and try again. Eventually it will light. Assuming the works are in good shape. Air flow switch (sail), gas valve, and ignitor are the three places which keep it from lighting. I'm sure the circuit board fails in some, but I've never seen a failed board.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Suburban furnace not starting, [message #339355 is a reply to message #339338] |
Thu, 06 December 2018 11:36 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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And now that IO think of it, you can tell how far the furnace gets by listening closely to it. When the 'stat calls for heat, you get a CLICK out of the furnace, and the blower spools up. As soon as there's airflow, you get another CLICK which is the gas valve opening and the igniter starts at the same time. Then you get a gentle WHUFF when the burner lights. How far it gets in the sequence gives an idea of what ain't working. (It's a stunt I learned on a particular brand of FM transmitters which have a very distinctive sounding start sequence) Just like cars, smell and sound are about as helpful as looking.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Suburban furnace not starting, [message #339357 is a reply to message #339354] |
Thu, 06 December 2018 12:06 |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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Senior Member |
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That’s what I thought, but then I discovered what must have been a problem
with the wiring between the thermostat and the furnace. I replaced wiring
that and all works. Same symptoms as you, same confirmation of continuity
through the thermostat using an ohm-meter, though I tested at the
thermostat because it was easier. :)
Rick “but I got a replacement furnace out of the deal” Denney
On Thu, Dec 6, 2018 at 11:24 AM Bob Dunahugh wrote:
> Can't be an issue with the thermostat. As covered below. OHM's meter
> confirmed it. And can't be the sail switch. As the fan doesn't come on at
> all. The sail switch is what turns the gas valve on after the fan is up to
> speed. Bob Dunahugh 78 Royale
>
> I checked the thermostat, and related 2 wires. OK. Have good 12 V power.
> Ground good. First thought was that the control board was the problem. But.
> I believe that the thermostat turns on a relay. That then turns on the 12
> V powers the control board. So I'm thinking that I need to send money to
> Jim at Applied. Jim will get me the correct part as usual. You SPARKIES
> think I got it correct? Bob Dunahugh
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
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