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| [GMCnet] Ghost-operated furnace [message #149757] |
Wed, 16 November 2011 01:06  |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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I went out to the motorhome to fetch some screws, and noticed that a fan
was running. It was the furnace blower. So, I figured last time I was in
the coach, I must have bumped the thermostat switch and turned it on. Nope,
it was off. I pulled the thermostat cover and confirmed that "off" meant
"off".
Left with no other way to make the furnace blower stop, I pulled the fuse
on that circuit. Whatever ghost was making it run then decided to take a
break.
My furnace, which is maybe a 15-year-old Suburban, has stopped working a
year or so ago (maybe more), and I've had it on the list to pull it for a
while to figure it out. My furnace is mounted in a non-standard spot, under
the cook top in the corner of my L-shaped galley counter. It's not easy to
access it at all, so I've put it off. For the little bit of heat that I
only occasionally need, the heat strip in the roof air has been adequate to
take off the chill.
The previous symptoms were the usual: Blower would start but the gas valve
would never open. The electronic starter was working, though I has probably
tried to start that furnace about a million times in the who-knows-how-long
period it was running. Could have been the sail switch, but I don't know.
But now I guess I'll have to pull it and figure out what's going wrong with
it.
Anybody ever heard of the furnace running with the thermostat turned off?
Other than the thermostat wire being chewed by a $%&%(*&#! mouse, that is.
Rick "afraid the kitchen counter was built around the furnace by the PO's
PO" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Ghost-operated furnace [message #149760 is a reply to message #149757] |
Wed, 16 November 2011 02:16  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Rick,
This is just a wild guess but inside the furnace is a thermal that keeps the fan running after the thermostat shuts off. Its purpose is to keep the fan going until the heat exchanger has cooled down. I'm wondering if that thing or the circuit to it is bad. I had one go bad on a house furnace one time with similar symptoms.
Other thoughts are a tacked relay point or a broken spring on a blower motor relay.
I have never been in a Suburban so I'm really just guessing.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Ghost-operated furnace [message #149762 is a reply to message #149760] |
Wed, 16 November 2011 02:46 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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I would bet on mice, not ghosts. When I first tried to make the original
suberban furnace in my 78 Royale work, the fuse was blown. When I replaced
the fuse, the fan motor immediately started. Aha, I thought, problem
solved. Nope, it did not light. So, much tinkering, frustration, finally
read the manual. Gave up procrastinating and pulled it out. Took it apart.
Found fried mouse in the near vicinity of the high tension lead to the
ignitor, and a fried circuit board. Replaced the board with a dinosaur one,
along with the electrode that goes into the burner and the sail switch. Mud
daubers had built extensive colonies in the heat exchanger, and fought that
for quite a while. Finally got it to light off, and it would run until the
unit got quite warm and then the burner would go out, and the fan would
continue to run and not stop. Reasoned that it must be the high limit
switch, and replaced that. Same deal. Ordered a new replacement furnace and
thermostat. That fixed the problem. My advise for anyone that is working on
an original furnace that is a problem is. Do what I did without the first
part of the problem. Take the old furnace out, and replace it and save
yourself the hassle. The new ones have more safety features, and do not
have cracked heat exchangers that you can't see that could emit carbon
monoxide into your living space and kill you in your sleep. Also add a
carbon monoxide detector to your coach while you are at it.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Nov 16, 2011 at 12:16 AM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> Rick,
>
> This is just a wild guess but inside the furnace is a thermal that keeps
> the fan running after the thermostat shuts off. Its purpose is to keep the
> fan going until the heat exchanger has cooled down. I'm wondering if that
> thing or the circuit to it is bad. I had one go bad on a house furnace one
> time with similar symptoms.
>
> Other thoughts are a tacked relay point or a broken spring on a blower
> motor relay.
>
> I have never been in a Suburban so I'm really just guessing.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Ghost-operated furnace [message #149767 is a reply to message #149760] |
Wed, 16 November 2011 06:57 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Ken Burton wrote on Wed, 16 November 2011 00:16 |
... inside the furnace is a thermal that keeps the fan running after the thermostat shuts off. Its purpose is to keep the fan going until the heat exchanger has cooled down. I'm wondering if that thing or the circuit to it is bad. ...
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I had this switch go bad in my '78. I was lucky enough to have the furnace from the '77 to use for troubleshooting.
It is a little bigger than a quarter with two (or three) terminals on it. (The one found in the '77 had three terminals... one unused, but works with two.) Fairly easy to swap... two screws... once you have the furnace out.
But think about it... you say it is a hard to access space. It is old. Do you really want to dig in there for the next thing that goes bad? Maybe it would be best to take JimH's advice... and replace it with new.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
[Updated on: Wed, 16 November 2011 06:58] Report message to a moderator |
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| Re: [GMCnet] Ghost-operated furnace [message #149852 is a reply to message #149762] |
Wed, 16 November 2011 22:54 |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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Senior Member |
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On Wed, Nov 16, 2011 at 3:46 AM, James Hupy <jamesh1296@gmail.com> wrote:
> My advise for anyone that is working on
> an original furnace that is a problem is. Do what I did without the first
> part of the problem. Take the old furnace out, and replace it and save
> yourself the hassle.
>
Thanks, but my furnace is not original. It's perhaps a dozen years old,
maybe 15. But it's probably identical to the ones you'd buy now, with the
same features, safety and otherwise.
Clearly, I need to get enough access to it to inspect its insides. Out
comes the cook-top, which is above it. I think if I pull that cook-top, I
may be able to get to the control board and the various switches without
having to disassemble my galley, which I think was built around it two
owners ago.
Rick "who can live with the heat strip in the roof air for a long time
before replacing the furnace out of hand" Denney
--
'73 230 "Jaws"
Northern Virginia
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