Home » Public Forums » GMCnet » Furnace problems
| Furnace problems [message #106962] |
Sun, 28 November 2010 19:23  |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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Just got back from our first pretty darn successful camping trip. Only had two issues I'll only address one in this thread. It was in the low 30s and it was a bummer not having the furnace with the wife and two small kids, but we were creative and stayed warm.
We have a Sub NT-30SP LP furnace. No pilot light. Elect ignition.
Turn thermo to desired temp, furnace gets to temp no problems. Blows Super Hot Air.
After a while camper cools off and thermo tells it to turn back on.
This time and every other time it blows cold air and never lights. Don't even hear it clicking to try to ignite.
I manually turn thermostat to the off position, adjust temp setting and furnace will fire up and work great.
When it tells it to turn back on after that, blows cold air. It never tries to light.
I cleaned the burner, and cleaned the spark probes.
I'm thinking its the control board?
Any ideas???
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: [GMCnet] Furnace problems [message #106964 is a reply to message #106962] |
Sun, 28 November 2010 19:38  |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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On Nov 28, 2010, at 6:23 PM, Michael wrote:
>
>
> Just got back from our first pretty darn successful camping trip. Only had two issues I'll only address one in this thread. It was in the low 30s and it was a bummer not having the furnace with the wife and two small kids, but we were creative and stayed warm.
>
> We have a Sub NT-30SP LP furnace. No pilot light. Elect ignition.
> Turn thermo to desired temp, furnace gets to temp no problems. Blows Super Hot Air.
> After a while camper cools off and thermo tells it to turn back on.
> This time and every other time it blows cold air and never lights. Don't even hear it clicking to try to ignite.
> I manually turn thermostat to the off position, adjust temp setting and furnace will fire up and work great.
> When it tells it to turn back on after that, blows cold air. It never tries to light.
> I cleaned the burner, and cleaned the spark probes.
> I'm thinking its the control board?
> Any ideas???
I believe your furnace has a "sail switch". This is a little micro switch attached to a vane. When your furnace first tries to light the fan blows against this sail (vane) and connects the circuit through the switch. This is a safety feature so that If there were no air flow then the burner would not ignite. If the switch is bad or a wire is loose from it then the furnace will not light.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: Furnace problems [message #106967 is a reply to message #106962] |
Sun, 28 November 2010 19:56 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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Is it a part of the control board? I did a little research and it looks like "dinosaur electronics" makes a replacement board for my furnace for about $100 I don't want to spend that if its just a inexpensive switch.
I'm guessing my furnace wasn't used much. It looks like it is from 1990 (just a guessby some of the wording on the stickers like wheat year certified it was in) The unit works great when it works! lol
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: Furnace problems [message #106973 is a reply to message #106962] |
Sun, 28 November 2010 20:18 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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Thought of low voltage but its a brand new group 27 battery. I didn't have a volt meter with me at the time, but everything else worked great and all the batteries are brand new. It didn't work from the first night. We used ultra little power between setting up camp and the first turn on, we have all LED bulbs inside and didn't run anything.
It always lights up the first time. Anytime even on day four the first light up would work great. But then the next time it called to turn on just cold air.
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: [GMCnet] Furnace problems [message #106977 is a reply to message #106973] |
Sun, 28 November 2010 20:37 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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I agree with Gene, These units do not like to ignight if the voltage
is below 13 volts.
On Sun, Nov 28, 2010 at 6:18 PM, Michael <radioactive626@msn.com> wrote:
>
>
> Thought of low voltage but its a brand new group 27 battery. I didn't have a volt meter with me at the time, but everything else worked great and all the batteries are brand new. It didn't work from the first night. We used ultra little power between setting up camp and the first turn on, we have all LED bulbs inside and didn't run anything.
> It always lights up the first time. Anytime even on day four the first light up would work great. But then the next time it called to turn on just cold air.
> --
> 1973 23' Sequoia
> _______________________________________________
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--
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 problems [message #106980 is a reply to message #106962] |
Sun, 28 November 2010 20:50 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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Hu, not arguing but then why could I start it by shutting it off, then turning it back on?
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: [GMCnet] Furnace problems [message #106983 is a reply to message #106962] |
Sun, 28 November 2010 21:01 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Michael, remove the end cover and look at the wire that goes to the igniter.
If there is only one wire, then the igniter grounds back through the
screw(s) that hold the heat exchanger to the furnace housing. Check to see
if that screw(s) is/are tight. I put a separate ground wire on mine when it
was doing the same thing and it cured it. When the sail switch operates, it
closes the ignitor circuit. If the motor is running slowly like it might
when the battery voltage is low, then the sail switch will stay open and the
ignitor will not function. Slow motor speed can also be caused by a tight
bearing in the motor or high resistance in the circuit. Check all the
twistlok connectors and grounds as well. Hope this helps.
Jim Hupy
Salem, Or
78 Royale 403
On Sun, Nov 28, 2010 at 5:23 PM, Michael <radioactive626@msn.com> wrote:
>
>
> Just got back from our first pretty darn successful camping trip. Only had
> two issues I'll only address one in this thread. It was in the low 30s and
> it was a bummer not having the furnace with the wife and two small kids, but
> we were creative and stayed warm.
>
> We have a Sub NT-30SP LP furnace. No pilot light. Elect ignition.
> Turn thermo to desired temp, furnace gets to temp no problems. Blows Super
> Hot Air.
> After a while camper cools off and thermo tells it to turn back on.
> This time and every other time it blows cold air and never lights. Don't
> even hear it clicking to try to ignite.
> I manually turn thermostat to the off position, adjust temp setting and
> furnace will fire up and work great.
> When it tells it to turn back on after that, blows cold air. It never tries
> to light.
> I cleaned the burner, and cleaned the spark probes.
> I'm thinking its the control board?
> Any ideas???
> --
> 1973 23' Sequoia
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: Furnace problems [message #106986 is a reply to message #106962] |
Sun, 28 November 2010 21:18 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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I'll do that Jim. I'll check into that this week for sure!
Hey just noticed your from Salem. I own a house in sunny side by the shirley middle school in south salem. We don't live there now, we are back in AZ full time. But people rent our house there.
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: [GMCnet] Furnace problems [message #106989 is a reply to message #106980] |
Sun, 28 November 2010 21:20 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Michael, the control board is a sequential device. A number of things have
to be happen before the the ignition sequence can take place. When you start
up from clear cold, the following things happen in sequence. First the fan
motor starts. At the same time an electronic timer sequence is initiated,
the purpose of which is to do two things. One is to turn on the gas valve
solenoid after a delay. The second is to operate the ignition coil so that
when the gas will ignite when the valve opens. The sail switch circuit is in
fact a safety device that insures there is the correct amount of combustion
air as well as air supplied to the heat exchanger and ductwork. If the motor
speed is too slow due to the things I mentioned earlier, then the gas valve
will remain closed, the ignition may or may not activate, and the fan will
continue to run until you manually shut off the thermostat and restart the
sequencer. Sounds complex & it is to some degree. These things are voltage
sensitive & really like fully charged batteries to work correctly. It is
very possible to have nearly new batteries that are not fully charged. Check
& eliminate the possibilities one by one. Good luck.
Jim Hupy
Salem, Or
78 Royale 403
On Sun, Nov 28, 2010 at 6:50 PM, Michael <radioactive626@msn.com> wrote:
>
>
> Hu, not arguing but then why could I start it by shutting it off, then
> turning it back on?
> --
> 1973 23' Sequoia
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: Furnace problems [message #106992 is a reply to message #106962] |
Sun, 28 November 2010 22:07 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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What should be the batt voltage to operate the furnace?
I'll check it but I just can't see how its low voltage. Only cause after a 100+ mile trip the batteries are charged...
If it was low voltage would I be able to shut it off and turn it back on to have it work?
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: Furnace problems [message #106995 is a reply to message #106992] |
Sun, 28 November 2010 22:25 |
idrob
Messages: 645
Registered: January 2005
Location: Central Idaho
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| MrRadioActive wrote on Sun, 28 November 2010 20:07 |
What should be the batt voltage to operate the furnace?
I'll check it but I just can't see how its low voltage. Only cause after a 100+ mile trip the batteries are charged...
If it was low voltage would I be able to shut it off and turn it back on to have it work?
|
The furnace needs at least 11.5 volts AT THE FURNACE to work properly. It is not uncommon for the voltage to be low due to poor connections, poor fuses, bad grounds and so on. This may be your issue.
Second thing that has not been mentioned is the overtemp Klixon switch. You said the furnace blows "super hot air". If so, it may be cycling on the over temp switch due to poor ductwork, or a slow fan due to age. It is very common for the over temp Klixon switch to open to cycle the furnace then when it closes it really does not make good internal contact and the thing will not start again by itself. Cycling the thing, for some reason, often makes it work again.
So, check voltage, check the sail switch, and check the over limit switch. The overlimit switch is hard to test, they get erratic and just need to be replaced out of principle sometimes (sorry, I am not a parts changer, but these are hard to check).
I doubt that it is your board, but stranger things have happened. If the furnace is old, old, you might just be better off changing it out altogether. Does not take long to put more money into it than it is worth.
Rob Allen
former owner of '76 x-PB
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| Re: Furnace problems [message #106996 is a reply to message #106962] |
Sun, 28 November 2010 22:34 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
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I think the furnace by all indications is from 1990. Ill check voltage, and grounds. DC wiring is fairly easy for me. My brain just can't register that it works when I turn it on and shut it off. But stranger things have happened~~~ I'll start by checking fuse connections and voltage. Then switches.
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: [GMCnet] Furnace problems [message #107001 is a reply to message #106996] |
Sun, 28 November 2010 23:13 |
Terrance Boyd
Messages: 38
Registered: October 2008
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Micheal, have you tried the furnace when pluged into shore power? Maybe that
would eliminate the possibility of low battery voltage. Does the furnace
shut down completely or just continue to blow cold air when it reaches temp.
The reason I ask, is mine would was acting similarly, but would continue to
blow air until it was turned off and on. It was like the thermostat would
open momentarily,just enough to shut the gas solenoid, but not long enough
to shut down other things. I made an ajustment on the anticipator in the
thermostat. That was three weeks ago, it has when working every night since.
Terry
On Sun, Nov 28, 2010 at 9:34 PM, Michael <radioactive626@msn.com> wrote:
>
>
> I think the furnace by all indications is from 1990. Ill check voltage, and
> grounds. DC wiring is fairly easy for me. My brain just can't register that
> it works when I turn it on and shut it off. But stranger things have
> happened~~~ I'll start by checking fuse connections and voltage. Then
> switches.
>
> --
> 1973 23' Sequoia
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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List Information and Subscription Options:
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| Re: Furnace problems [message #107014 is a reply to message #106962] |
Mon, 29 November 2010 06:23 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I have had several different furnaces on several different coaches fail the same way your is. They all came down to three things.
1. Motor bearings. - Oil them
2. Sticking sail switch. - The next time if fails, rap on the furnace during start up and see if it fires up correctly.
3. Low voltage. - Start the engine or plug in to shore power to bring up the voltage and see if it starts correctly.
You might also read the voltage at the furnace during start-up and see what it is. I think you need something over 11.75 or so. If the voltage is low, read it again at the battery and see what it is there during start-up. If the voltage is good at the battery and low at the furnace you need to find the drop. the drop can be in the ground circuit or anything in the +12 volt circuit.
I doubt it is a bad board.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Furnace problems [message #107024 is a reply to message #106962] |
Mon, 29 November 2010 08:57 |
fred v
Messages: 999
Registered: April 2006
Location: pensacola, fl.
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go here:
http://bdub.net/manuals/index.html
download the manuals for the furnace. it sounds like you are going into "lockout". mine did the same exact thing. it would not light after satisfying the temp. i found that my board was shot. the initial time delay was not happening and the ignition would not ever turn off. the new dyno board fixed it all.
you can take the front cover off and look through the little window near the sparker and watch to see it it sparks when the thermostat call for heat again.
Fred V
'77 Royale RB 455
P'cola, Fl
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| Re: Furnace problems [message #107026 is a reply to message #106962] |
Mon, 29 November 2010 09:10 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
Karma: 0
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I'm going to take it apart soon. It does continue to blow cold air when its "not working" I'll check the voltages, and switches. I have tried to short the wires together at the thermostat it turned on but didn't light.
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: Furnace problems [message #107071 is a reply to message #107026] |
Mon, 29 November 2010 18:28 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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As you can tell from the suggestions you have been given a rather minor drop in DC voltage will cause it to not relite. I think you should start with the suggestion of connecting to shore power and see if it operates normally on the thermostat for several cycles. This will give a good indication if it is a low battery problem or something else. A nice feature of the Dinosaur boards is it will try to start the igniter 3 or 4 times rather then 1 try of many original Suburban boards. Also you can get the one with the fan lockout feature if it doesn't light so the fan doesn't blow cold air all night).
I found my furnace had voltage drops in the ground circuit,the 12 volt wire from the fuse panel, and the thermostat wires. I added a heavy ground wire and a #8 wire from the fuse panel to the furnace. I also replaced the thermostat with a digital thermostat and added a thermostat relay at the furnace to get rid of the 1 volt loss in the thermostat wires(the digital thermostat was a nice option).These changes made a big difference in being able to use the furnace dry camping.Also you only have 1 battery? I have 2 golf cart battery's.
Another thing no one seems to have a problem with. When it was real cold my gas valve would stick closed,it took me awhile to figure that one out. I took the valve apart and cleaned the seat with alcohol then applied graphite film to the seat. It always works now.Some folks probibly should replace the valve with a new one if they have this problem but I used to fix furnaces for a living so messing with gas valves doesn't worry me.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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