Fan only addition for furnace

T

tyler

Active member
Jun 22, 2013
513
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Has anyone added a manual control (on/off) to just the fan on a Suburban furnace?

I have a Suburban NT30 in both coaches. When I am paying for electricity at a campsite, I want the electric to heat the coach. A little cube heater
usually provides enough BTUs for the temps we camp in, but a single source in a long space is not the most comfortable. I would like to turn on the
furnace fan simply as circulation (and even some white noise for sleeping).

Seems like a simple 12 volt source wire could be switched into the line right before the fan. But I don't want to backfeed or mess up the control
board.

Thoughts, examples or alternatives for this?

Any suggestions for a replacement bathroom loop booster fan (behind the stove on a GMC upfit) are appreciated as well.
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
 
The Suburban Service Manual shows the motor power coming directly from the control board. Therefore without a control board schematic I can't tell if
applying 12V to the motor would "Feedback" into the control board and cause damage. Other models show an external relay which would be no problem.

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

On the other hand, my experience with the air flow on our Suburban furnace is very poor. The high limit switch on the heat exchanger trips off the
flame continually. There is not much airflow out of the vents. The ductwork is open so I'm guessing the turbulent airflow is the problem.

One time we were inside on a cold rainy afternoon trying to keep warm and dry. So I opened the access panel on the front to the furnace and WOW!!! the
air and heat that came out was overwhelming! The coach warmed up in minutes and the thermostat finally got to do its job regulating the now nice warm
interior. Since then I've left the front cover off the furnace and when we want to use it, we just open the door. The fan blows lots of air and it
takes very little time to warm the coach up. It consumes very little propane as well.

So the ducts and vents are open. With the front cover on and the duct disconnected, not much air comes out right at the furnace. This is why I'm
thinking the turbulent air inside is the cause. I've thought about having a sheet metal ductwork made to fit along the inside front of the cabinets
and under the front couch, like home ductwork. I'd have the ductwork connect directly to the front of the furnace. Maybe it would give more laminar
(less turbulent) airflow to the vents.

Just my experience.

I'm assuming you will be plugged into grid power, so maybe just a 120V fan might be an answer to your issue.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Kevin,
You could be adding a function that could possibly bypass the safety functions of the control board.

What I do to move the air around the coach when I have the heater running is to put the AC on low fan and us it/them to recirculate the air which being hot is at the top lot the coach whereas the air for the furnace is at floor level and is much colder. Running the AC fan on low as hot air is easier too move than cold and you have white noise too!. I also have heat strips (5000W) in each of my AC units and they are very good too.

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan

>
> Has anyone added a manual control (on/off) to just the fan on a Suburban furnace?
>
> I have a Suburban NT30 in both coaches. When I am paying for electricity at a campsite, I want the electric to heat the coach. A little cube heater
> usually provides enough BTUs for the temps we camp in, but a single source in a long space is not the most comfortable. I would like to turn on the
> furnace fan simply as circulation (and even some white noise for sleeping).
>
> Seems like a simple 12 volt source wire could be switched into the line right before the fan. But I don't want to backfeed or mess up the control
> board.
>
> Thoughts, examples or alternatives for this?
>
> Any suggestions for a replacement bathroom loop booster fan (behind the stove on a GMC upfit) are appreciated as well.
> --
> 1975 Glenbrook, 1978 Royale rear bath
> Raleigh, NC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
J.R., Great idea on using the A/C on fan only mode to distribute the heat.

I'm thinking you meant 500watts for the heat strips. We have them and they certainly help.

Now if they were 5kw strips that would certainly warm things up!

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Bruce,
Nope, they are 5000 watt units and they are dometic brand.

JR

>
> J.R., Great idea on using the A/C on fan only mode to distribute the heat.
>
> I'm thinking you meant 500watts for the heat strips. We have them and they certainly help.
>
> Now if they were 5kw strips that would certainly warm things up!
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
In order for the furnace to blow it needs make up air. If your furnace
blows way harder with the front panel open you likely have an obstruction
in the return duct

Sully
Bellevue wa

On Sun, Jan 10, 2021 at 11:31 AM John Wright via Gmclist <

> Bruce,
> Nope, they are 5000 watt units and they are dometic brand.
>
> JR
> > On Jan 10, 2021, at 11:55 AM, Bruce Hislop via Gmclist <

> >
> > J.R., Great idea on using the A/C on fan only mode to distribute the
> heat.
> >
> > I'm thinking you meant 500watts for the heat strips. We have them and
> they certainly help.
> >
> > Now if they were 5kw strips that would certainly warm things up!
> >
> > --
> > Bruce Hislop
> > ON Canada
> > 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> > http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> > My Staff says I never listen to them, or something like that
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
On the suburban furnaces, if all 4 hose outputs are not used, they will
frequently cycle on and off. There is one knock out that is usually not
open, and what I did on mine was knock it out and ran another duct hose to
a cooler part of the coach. That stopped the on/off cycling on my furnace.
Jim Hupy
Salem, Oregon

On Sun, Jan 10, 2021, 12:12 PM Todd Sullivan via Gmclist <

> In order for the furnace to blow it needs make up air. If your furnace
> blows way harder with the front panel open you likely have an obstruction
> in the return duct
>
> Sully
> Bellevue wa
>
> On Sun, Jan 10, 2021 at 11:31 AM John Wright via Gmclist <

>
> > Bruce,
> > Nope, they are 5000 watt units and they are dometic brand.
> >
> > JR
> > > On Jan 10, 2021, at 11:55 AM, Bruce Hislop via Gmclist <

> > >
> > > J.R., Great idea on using the A/C on fan only mode to distribute the
> > heat.
> > >
> > > I'm thinking you meant 500watts for the heat strips. We have them and
> > they certainly help.
> > >
> > > Now if they were 5kw strips that would certainly warm things up!
> > >
> > > --
> > > Bruce Hislop
> > > ON Canada
> > > 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> > > http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> > > My Staff says I never listen to them, or something like that
> > >
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Return air is from the general under couch area. On one trip we packed with spares in boxes, TP, 14-50 extension cord etc neatly packed under the
couch. It was down to the teens snd the furnace kept tripping the high limit and blowing cold. Simply moving items away from the furnace allowed air
to come in behind couch and over to furnace. No more problems.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
JR,

5000 watts is over 40 amps at 120 volts. Maybe the 5000 is btu/h? That's more in line with the typical space heater being under 1500 watts and about
5000 btu/h.

Richard
--
'77 Birchaven TZE...777;
'76 Palm Beach with 18,477 verified miles;
‘76 Edgemonte
 
Return air should not be a problem. We have a Palm Beach with the louvered doors and the side is wide open to the couch for plenty of return air.

I put my hand over the outlets and yes I can feel warm air but very little volume of air. Open the front and WOW! lots of hot air volume. Again just
my experience. Mine is a SF30 model I believe (low and wide).

5000 watt heat strips infer electric resistance heating elements, not a heat pump. 5Kw = ~42 amps at 120Vac so no way you can power one A/C on heat
from a 30Amp supply... may it has options to run on 120VAC at lower wattage? So at a 50Amp 240VAC source you would be looking at 21Amps for one unit
and 42 amps for both units. So I'm guessing the A/C (motors and compressor) run on 120VAC so you can use the Onan and 30Amp service. The heat would
only work on 240VAC @50Amps? Even so you would be limited for operation of other appliances on a 50Amp service. No electric water heater, nor
microwave... a toaster might be marginal. Has that been an issue since the main breakers are only 40Amp?

I can't find unit on the Dometic site with at 5kw heat strip, they don't even spec their heating capabilities except to say the units operates on
115VAC.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
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