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Open Roads Forum  >  Tech Issues

 > Need help with a SF 30 Suburban Furnace

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enblethen

Moses Lake, WA

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Joined: 01/05/2005

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Posted: 11/17/20 11:43am Link  |  Quote  |  Print  |  Notify Moderator

Good explanation, Doug
I think the OP is in over his head!


Bud
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Pace Arrow

2003 Chev Ice Road Tracker


mikestock

Vestavia Hills, AL, USA

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Posted: 11/17/20 04:32pm Link  |  Quote  |  Print  |  Notify Moderator

emblethen wrote:

I think the OP is in over his head!

So clairvoyant. You remind me of my wife.

I received the new Coleman thermostat today and installed the it. The circuit board was identical to the one I replaced and everything works perfectly. I still don't know the exact problem with the old thermostat but the new replacement solved it.

I had already eliminated the most common causes, the sail switch, the over temperature switch or dirt dabbers. The furnace would work when I applied 12v. using an external battery source, so it left only the thermostat or some unlikely cause, like rats.

* This post was edited 11/17/20 06:09pm by mikestock *

enblethen

Moses Lake, WA

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Posted: 11/17/20 06:56pm Link  |  Quote  |  Print  |  Notify Moderator

Glad to hear that you have resolved your issue.

dougrainer

Carrolton, Texas

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Posted: 11/18/20 05:48am Link  |  Quote  |  Print  |  Notify Moderator

mikestock wrote:

emblethen wrote:

I think the OP is in over his head!

So clairvoyant. You remind me of my wife.

I received the new Coleman thermostat today and installed the it. The circuit board was identical to the one I replaced and everything works perfectly. I still don't know the exact problem with the old thermostat but the new replacement solved it.

I had already eliminated the most common causes, the sail switch, the over temperature switch or dirt dabbers. The furnace would work when I applied 12v. using an external battery source, so it left only the thermostat or some unlikely cause, like rats.


I think you stated you may have caused a backfeed short when you were diagnosing the Furnace system. That may have blown something on the tstat circuit board. Have you looked at the Tstat circuit board for any burn spots? Doug

mikestock

Vestavia Hills, AL, USA

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Posted: 11/18/20 06:27am Link  |  Quote  |  Print  |  Notify Moderator

Yes

Flyfisherman128

Broadalbin, NY

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Posted: 11/18/20 09:07pm Link  |  Quote  |  Print  |  Notify Moderator

So you are saying you got gas and spark but no fire.. I just put a new motor (it was going bad)I thought I want getting the correct air flow. I replaced the sail switch. Finally I replaced the igniter. I set the igniter where it was set at the factory. I still got it light intermittently. Not a good scenario for winter. I got out the owners manual and set the igniter as specified which was not even close to the way it came from the factory..yet it worked for 20 years.. To my surprise, problem solved.

mikestock

Vestavia Hills, AL, USA

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Posted: 11/19/20 06:29pm Link  |  Quote  |  Print  |  Notify Moderator

No gas.

It seemed that most of the many posts about Suburban furnaces claimed the same problem as I had. The fan came on and I couldn't hear the igniter sparking above the fan noise. I could smell no gas on the outside. Most every bit of information I read said and the circuit diagram showed that the over temperature thermostat and the sail switch were usually the culprits. I removed the furnace from the housing and set it up on a bench, running it with a 12v battery. The spark looked good but, of course, there was no gas. Everything looked good so I reinstalled it and it was just like before. No gas. I let two wires touch and then nothing worked, no fan, no nothing. I found the glass fuse in the thermostat and I was back to the original situation; fan ran, no heat. I took a chance that it must be the thermostat so I bought a new one identical to the OEM and everything works. End of story. I don't really know what was wrong with the thermostat and don't care. It works.

I had a previous problem with this furnace about 3 years ago. Found, what felt like, a 1/4 lb dirt dabber nest in the duct. Put screens on the outside to prevent this from happening again.

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