| Furnace ground location [message #306414] |
Fri, 02 September 2016 22:55  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Where is my furnace grounded to my house frame? The four wire connection heads back under/behind the unit towards fuse panel and closet out of sight.
My propane furnace runs fine when engine or genny are running, or plugged into shore power. Battery power alone will not heat. Thermostat demands, it starts fan, but no heat ever builds up, yet fan keeps running. I have taken it all apart a couple times over the years...when I first bought it to verify no wasp nest blockage or firebox degradation and resultant carbon monoxide threat. My current theory is sail switch isn't getting enough fan speed to allow it to light with a weak ground that external sources provide enough voltage to overcome, and battery alone does not.
I think it is a Suburban NT30 or NT40, but the ground I am guessing is original as the four wire is spliced near furnace from old to new.
1975 Glenbrook 26 with rear bed and wet side bath. Kitchen is right in front of you as you come in the door. Furnace is below the sink, thermostat is on driver side rear facing wall in bed space.
My main question stands for ground location, but various troubleshooting, alternatives and general goofy comments ("use more blankets" comes to mind) are welcome.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: [GMCnet] Furnace ground location [message #306416 is a reply to message #306414] |
Sat, 03 September 2016 00:28  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Two wires are from the thermostat.
Other is positive and negative.
On Fri, Sep 2, 2016 at 8:55 PM, Tyler wrote:
> Where is my furnace grounded to my house frame? The four wire connection
> heads back under/behind the unit towards fuse panel and closet out of sight.
>
> My propane furnace runs fine when engine or genny are running, or plugged
> into shore power. Battery power alone will not heat. Thermostat demands, it
> starts fan, but no heat ever builds up, yet fan keeps running. I have
> taken it all apart a couple times over the years...when I first bought it to
> verify no wasp nest blockage or firebox degradation and resultant carbon
> monoxide threat. My current theory is sail switch isn't getting enough fan
> speed to allow it to light with a weak ground that external sources
> provide enough voltage to overcome, and battery alone does not.
>
> I think it is a Suburban NT30 or NT40, but the ground I am guessing is
> original as the four wire is spliced near furnace from old to new.
>
> 1975 Glenbrook 26 with rear bed and wet side bath. Kitchen is right in
> front of you as you come in the door. Furnace is below the sink, thermostat
> is
> on driver side rear facing wall in bed space.
>
> My main question stands for ground location, but various troubleshooting,
> alternatives and general goofy comments ("use more blankets" comes to mind)
> are welcome.
> --
> 1975 Glenbrook
> Raleigh, NC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: Furnace ground location [message #306420 is a reply to message #306414] |
Sat, 03 September 2016 01:16 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I have never had to chase that ground lead down so I do not know exactly where that wire is located. When running on the battery you are already starting out at a lower voltage than what is available from the converter on shore or generator power. The converter is putting out 13.8 to 14.0. A fully charged battery will only so 12.6 or so. So you are starting out oat a 1.4 volt or so disadvantage if everythignos good in the supply circuit and you battery is fully charged.
If the voltage is low at the furnace the igniter and gas valve will not energize. So you are right to look for any voltage drop there might be going to the furnace. Because I do not know where that ground wire attaches, I might go at it by simply adding an new one.
Before I did that I would check the voltage across the battery when trying to run the furnace and the voltage at the furnace when trying to run it. That should tell you if you have too much voltage drop in the circuit going to the furnace.
Corroded or oxidized ground connections are common in the GMC.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Furnace ground location [message #306453 is a reply to message #306414] |
Sat, 03 September 2016 13:18 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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Senior Member |
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Start by checking your voltage with house batteries vs on shore power. I predict you will see a difference.
As I recall the ignition boards have a voltage threshold below which they will not function. Too long ago to remember what it is for sure, but I seem to recall it being ~11v.
The fan will run at far lower voltage, albeit slowly.
They dont really pull many amps, so IDK if the ground plays that much of a role in this case, but as previously pointed out, you can just make a redundant ground.
76 Glenbrook
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| Re: Furnace ground location [message #306494 is a reply to message #306454] |
Sun, 04 September 2016 04:29 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Yes, there is. But he needs to be sure that he is not below the required start up voltage first. I had one that I moved in the dead of winter for someone that had a slightly binding motor. It would not trigger the sail switch when running just on the battery even though the voltage to the furnace was acceptable. My temporary solution was to start the engine to bring up the voltage and get the furnace going. After that I could turn off the engine and the furnace would continue to run.
After I delivered the coach the new owner dug into it and lubricated the motor. That took care of the problem.
I had another non-GMC one I was delivering do the same thing. All I had to do on that one was kick the furnace to get the sail switch to change.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Furnace ground location [message #306502 is a reply to message #306494] |
Sun, 04 September 2016 09:50 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Ken Burton wrote on Sun, 04 September 2016 04:29Yes, there is. But he needs to be sure that he is not below the required start up voltage first. I had one that I moved in the dead of winter for someone that had a slightly binding motor. It would not trigger the sail switch when running just on the battery even though the voltage to the furnace was acceptable. My temporary solution was to start the engine to bring up the voltage and get the furnace going. After that I could turn off the engine and the furnace would continue to run.
After I delivered the coach the new owner dug into it and lubricated the motor. That took care of the problem.
I had another non-GMC one I was delivering do the same thing. All I had to do on that one was kick the furnace to get the sail switch to change. Yep. My first post to this thread implied that the battery voltage needed to be checked. Still don't recall seeing where the battery voltage was checked and how much it was...
[Updated on: Sun, 04 September 2016 09:50] Report message to a moderator |
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| Re: Furnace ground location [message #306504 is a reply to message #306502] |
Sun, 04 September 2016 12:11 |
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Loffen
Messages: 1087
Registered: August 2013
Location: Norway
Karma: 1
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Senior Member |
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I did just go through my -73, not to much work as it is nearly empty inside, to me it looks the furnace wiring eventually goes in to the main harness and has the same ground point as everything else, near the cabinet where the fuses are and the countertop, I did just find two ground points and the other was from the main 110v braker box
1973 23' # 1848 Sky Blue Glacier called Baby Blue and a 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Green,
And sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway
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