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Author Topic: Suburban NT30M Furnace  (Read 1239 times)

flatlndr

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  • Posts: 25
Suburban NT30M Furnace
« on: February 26, 2012, 09:33:32 AM »
Hi all, anybody out there ever been into one of these old furnaces?? Trying to get this old girl ready for some early spring  camping.

The furnace in the old '82 Cross Country won't fire off. Suburban  NT30M . I'm plugged into shore power and am getting 13.3v to Tstat. Should both blue wires have 13.5 at the Tstat?. I assume its functioning ok since the fan runs. Fan runs fine. No ignition, no gas.  I dropped power to the Tstat before I pulled it in case it was in "lockout".  The power plug is a flat 3 prong. Have 13.3v at the plug end at furnace on the red/blue lead. 65lb. tank is full, just had it filled. Range/oven and refer works great. Freezer froze water in a couple hours. Ignitor doesn't
spark. I took it out and cleaned the contacts. On/off gas valve at furnace gas line is open and clear of obstruction.

 Pulled the furnace. Sail switch appears to make good contact when switch is moved manually. There's no continuity between the posts on the limit switch. Should there be w/ no power to the unit? I'm no electrician so am not sure of the terminology - normally open/closed, etc.
Thinking maybe the limit switch is stuck/bad not proceeding to the next sequence of letting the gas in and ignitor spark??

Not sure how to bench test everything i can with the unit out.  I've downloaded info on troubleshooting this furnace 
http://bryantrv.com/docs2/docs/subntnew.pdf 
but I'm a novice with this stuff.

Wondering if I took it to an RV service if they can bench test it. But, only want to do this as a last resort- kinda on a budget.

Also, while I have it out, would like to clean up the burner as I doubt the furnace has been used much. With only 26K on the rig and the PO didn't appear to be one to rough it much, it was probably used sparingly. I took out the 4 screws  the pdf say holds it in, but it didn't want to
slip out. Is there something else I'm missing, don't want to tear anything up.
Any suggestions on where I go from here is appreciated.
Thanks.
Tom B
Tom B.
Rossville, Ks.
1982 28' Cross Country by Sportscoach

Redbus

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  • Posts: 13
Re: Suburban NT30M Furnace
« Reply #1 on: February 26, 2012, 05:49:14 PM »
Being a R.V.I.A. Master Certified R.V. tech. retired I would recommend taking it to a service center. If you do not have the correct gas pressure you can blow the furnace apart and you're self with it.
That said you're problem is probably the circuit board NOT the thermostat if the fan runs.
1984 MCI 9 Home Conversion

flatlndr

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  • Posts: 25
Re: Suburban NT30M Furnace
« Reply #2 on: February 27, 2012, 08:51:42 AM »
Not really what I wanted to hear but after thinking about it, sage advice I'm sure.
Not afraid to admit defeat but better than the alternative.
At least I know a little more about how things are put together and what makes them work.
Will check out a local service center..
Thanks.
Tom B.
Rossville, Ks.
1982 28' Cross Country by Sportscoach

flatlndr

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  • Posts: 25
Update Re: Suburban NT30M Furnace
« Reply #3 on: March 02, 2012, 08:32:08 AM »
Thought I would update this for some of the old MH owners out there,,, and I mean the coach, not the person.

Going against advice and hearing about questionable service from some RV places, decided to try and diagnose this thing myself. Figured I can always take it in.  I'm not saying this is for everyone but these old coaches are pretty basic.
The most important thing is to use common sense SAFETY precautions when disconnecting/connecting the propane.

Rather than going into a long diatribe about  what was done, I'll just say that if a coach has spent most of its time sitting and the furnace doesn't work. pull it out and clean it up. Its not that hard to remove.
ALTHOUGH NOT ALWAYS THE CASE , the problem with this one was dirty contacts where the Tstat wire plugs into the board. The foil contacts on the board develop  a black or grey corrosion over time. You'll probably have to remove the board and clean them gently with a red rubber pencil eraser.  I also cleaned the ignitor probes with a small points file and adjusted the gap on the electrode. Don't use sand paper.
 No, this won't fix all problems but its an easy and cheap thing to check.
There are more things that can be checked - sail switch, limit switch, fan switch, thermostat, etc. etc. There's a lot of documentation out there
to troubleshoot. I figure I saved several hundred $ on this old rig and learned a lot along the way.
The DW will be happier knowing it will work if need be.

Tom B

 
Tom B.
Rossville, Ks.
1982 28' Cross Country by Sportscoach

Redbus

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  • Posts: 13
Re: Suburban NT30M Furnace
« Reply #4 on: March 02, 2012, 12:04:44 PM »
Tom
Glad it all worked out for you. I hope you put a new gasket after cleaning the ignitor probe. Carbon Monoxide poison is possibility if not.
1984 MCI 9 Home Conversion