Suburban furnace problems

[ghickey]

I have been starting to work on the Suburban furnace that is in my
coach. It is a SF-30 model and looks like it was fairly recent install
by the PO.

The problem I have had is that it will tend to heat for about a minute
and then shutdown. I am starting to believe that a good portion of my
problem is the thermostat (original). I have cleaned the thermostat a
bit and I am pretty much planning on replacing it with a round dial one
from a house.

But in playing and working on it the furnace was firing for about 5 mins
today. Still did not bring the heat up in the coach significantly even
though the thermostat was turned up all the way. After it shutdown the
blower continued to run. It ran for upwards of 10 mins before I killed
the furnace from the thermostat. Now I can see the blower running for a
minute or so to cool the burning chamber a bit and to get the last of
the excess heat, but it was blowing cold air for quite a while.

Does anyone have any thoughts on what might be going on? Is this still
an ignition problem where the furnace shuts down but still "thinks" it
is burning? I would say that it is just the time delay relay that needs
to be replaced if the furnace kept burning until the temperature got to
about where the furnace got to a point where it should shutdown.

Thanks.

--
Gerard Hickey / WTØF IRLP:3067/Echolink:529661
hickey DMR: 3102272
425-395-4554

 

[tyler]

This
http://www.bdub.net/manuals/Suburban_Service_Manual.pdf

more manuals on
http://www.bdub.net/manuals/

If you have not pulled it all the way apart (I mean down to the burners and fan out of the box) to check for wasp or other nests, it sounds like it is
firing but the sail switch is cutting off the burner from lack of air flow. Be sure to run all test with 12 volt charger running, don't count on your
battery voltage to be high enough if you are having any issues.

--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC

 

[bdub]

Tyler's right. As long as the thermostat is calling for heat, that fan
will keep on draining the battery.
Flame will shut down if the sail switch thinks it quit blowing, or low
voltage, or if the thermocouple thinks the fire has gone out.
I bet on the thermocouple in this case.

bdub

 

[Matt Colie]

>
> The problem I have had is that it will tend to heat for about a minute and then shutdown. I am starting to believe that a good portion of my
> problem is the thermostat (original). I have cleaned the thermostat a bit and I am pretty much planning on replacing it with a round dial one from a
> house.
>
>
> Thanks.
> --
> Gerard Hickey

Gerard,

If the thermostat you are proposing is one of the Honeywell rounds, look carefully. Most have a mercury switch. They are very attitude (the device,
not your) sensitive.

Then there is another possible PO induced issue. The thermostat a has a number stamped inside it. That is the value of the current that the device
expects to use for its "anticipator". It actually passes a small current through the bi-metal temperature measuring element so the thermostat does
not actually have to get up to the set point to shut off the heating cycle. The newer and older Suburbans have different values for this. That is
why Suburban ships and new one with a new heater. If the PO did not change it and it is way wrong, that can be some of your issue. I very much doubt
it is all of the issue you face.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[emerystora]

do not use a house thermostat. you might find the furnace “chattering”. The house thermostat will not take the vibration of the base .

You can buy one rom AppliedGMC or about and RV parts store or from Amazon and even Ace Hardware..

Emery Stora

>
> I have been starting to work on the Suburban furnace that is in my coach. It is a SF-30 model and looks like it was fairly recent install by the PO.
>
> The problem I have had is that it will tend to heat for about a minute and then shutdown. I am starting to believe that a good portion of my problem is the thermostat (original). I have cleaned the thermostat a bit and I am pretty much planning on replacing it with a round dial one from a house.
>
> But in playing and working on it the furnace was firing for about 5 mins today. Still did not bring the heat up in the coach significantly even though the thermostat was turned up all the way. After it shutdown the blower continued to run. It ran for upwards of 10 mins before I killed the furnace from the thermostat. Now I can see the blower running for a minute or so to cool the burning chamber a bit and to get the last of the excess heat, but it was blowing cold air for quite a while.
>
> Does anyone have any thoughts on what might be going on? Is this still an ignition problem where the furnace shuts down but still "thinks" it is burning? I would say that it is just the time delay relay that needs to be replaced if the furnace kept burning until the temperature got to about where the furnace got to a point where it should shutdown.
>
> Thanks.
>
> --
> Gerard Hickey / WTØF IRLP:3067/Echolink:529661

 

[hal stclair]

One of the problems can be you have multiple issues. Low voltage when RUNNING would be the first check you need to do. Checking grounds and plugs
would be a basic start. You could have a bad over temp switch, sail switch, thermocouple or any combination of those along with any number of other
maladies. After checking voltage you can simply jumper out the sail switch, over temp switch one at a time and work your way along. These things can
really drive you nuts although they really are quite simple machines. I've spent way more time working on some of these than I care to admit.
You can do it...
Hal
--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1975 Eleganza II, 101230,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM

 

[ghickey]

Yes, tell me about it! It would be so much nicer if the controller had a
few indicator lights on it to give an idea what it was seeing. That
ideally would narrow down what the problems could be.

It appears to me that the sail switch is good, but I have not tried to
throw a jumper across it. I was thinking this morning that I could hit
the over temp switch since it is right there.

Thanks for the thoughts.

--
Gerard Hickey / WTØF IRLP:3067/Echolink:529661
hickey DMR: 3102272
425-395-4554

> One of the problems can be you have multiple issues. Low voltage when RUNNING would be the first check you need to do. Checking grounds and plugs
> would be a basic start. You could have a bad over temp switch, sail switch, thermocouple or any combination of those along with any number of other
> maladies. After checking voltage you can simply jumper out the sail switch, over temp switch one at a time and work your way along. These things can
> really drive you nuts although they really are quite simple machines. I've spent way more time working on some of these than I care to admit.
> You can do it...
> Hal

 

[ghickey]

I am pretty sure the sail switch is working correctly. It stays closed
the entire time that the blower is running.

The coach is currently on shore power right now too. There is nothing
else powered up in the coach at the moment so I am not suspecting that
it is low voltage. Actually just about to start rewiring the entire
coach and the buzz box will be going away--it is inefficient and takes
up too much room.

I ended up putting screens on the exhaust and intake last year. It is
not clear but there looks there might be a bit of a mud dauber nest at
the curve in the plenum. I started to pull the furnace yesterday but a
PO hardwired the electrical and I did not want to pull it until I found
a plug to put in place of the butt connectors. Now that I have found a
suitable plug I can pull it the next time I am at the coach and open up
the burning chamber.

--
Gerard Hickey / WTØF IRLP:3067/Echolink:529661
hickey DMR: 3102272
425-395-4554

> This
> http://www.bdub.net/manuals/Suburban_Service_Manual.pdf
>
> more manuals on
> http://www.bdub.net/manuals/
>
> If you have not pulled it all the way apart (I mean down to the burners and fan out of the box) to check for wasp or other nests, it sounds like it is
> firing but the sail switch is cutting off the burner from lack of air flow. Be sure to run all test with 12 volt charger running, don't count on your
> battery voltage to be high enough if you are having any issues.
>

 

[johnny]

One other possibility. The furnace may be overtemping which will shut it down though the fan will still run. My new Suburban did this until I
noticed it had only one outlet connected, the others were blank flanged. This allowed enough air flow for the sail switch, but over time the burner
got too hot. I reconnected the unconnected vents (one floor one bathroom) and it has worked properly ever since. To check it, just take the ducts
loose and aim the outlet air away from the inlet on the front of the furnace and see if it stays lit.

--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

 

[ghickey]

Well, that is interesting..... There are 4 vents connected to the
furnace: 2 on the right side and 2 in front. I pulled the front off
(with the cabinet door open) and that is when it ran for 5 mins which
seems to me to be the longest that it has run. At least that is what it
seems to me.

Last fall at the Western States rally was the first time I had used it
(since I bought the coach) and at that point it was running for about a
minute and then it would shutoff for  a few minutes before it would turn
on again. So I wonder if it is a problem with the over temp switch and
maybe some airflow issues? I don't see any obvious signs of airflow
issues, but I do plan on replacing all the ducts while I am rewiring the
coach.

Hopefully this weekend I will have some better clues as to what the
problem is.

--
Gerard Hickey / WTØF IRLP:3067/Echolink:529661
hickey DMR: 3102272
425-395-4554

> One other possibility. The furnace may be overtemping which will shut it down though the fan will still run. My new Suburban did this until I
> noticed it had only one outlet connected, the others were blank flanged. This allowed enough air flow for the sail switch, but over time the burner
> got too hot. I reconnected the unconnected vents (one floor one bathroom) and it has worked properly ever since. To check it, just take the ducts
> loose and aim the outlet air away from the inlet on the front of the furnace and see if it stays lit.
>
> --johnny
>

 

[jim kanomata1]

I suspect that the ducts are choking the system and overheating.
I’m not sere if it has such.

On Tue, Mar 10, 2020 at 11:41 AM Gerard Hickey via Gmclist <

> Well, that is interesting..... There are 4 vents connected to the
> furnace: 2 on the right side and 2 in front. I pulled the front off
> (with the cabinet door open) and that is when it ran for 5 mins which
> seems to me to be the longest that it has run. At least that is what it
> seems to me.
>
> Last fall at the Western States rally was the first time I had used it
> (since I bought the coach) and at that point it was running for about a
> minute and then it would shutoff for a few minutes before it would turn
> on again. So I wonder if it is a problem with the over temp switch and
> maybe some airflow issues? I don't see any obvious signs of airflow
> issues, but I do plan on replacing all the ducts while I am rewiring the
> coach.
>
> Hopefully this weekend I will have some better clues as to what the
> problem is.
>
> --
> Gerard Hickey / WTØF IRLP:3067/Echolink:529661
> hickey DMR: 3102272
> 425-395-4554
>

> > One other possibility. The furnace may be overtemping which will shut
> it down though the fan will still run. My new Suburban did this until I
> > noticed it had only one outlet connected, the others were blank
> flanged. This allowed enough air flow for the sail switch, but over time
> the burner
> > got too hot. I reconnected the unconnected vents (one floor one
> bathroom) and it has worked properly ever since. To check it, just take
> the ducts
> > loose and aim the outlet air away from the inlet on the front of the
> furnace and see if it stays lit.
> >
> > --johnny
> >
>
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--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502