Help, Again. Our Suburban Furnace MDL# NT30M with electronic ignition, works sometimes and sometimes it won't. The furnace will come on (blower) and will light sometimes and then the next time it won't. I took the igniter out and all connections and igniter rods and flame sensor rods all appear to be good. I had Tricia work the thermostat while I lay in front of the furnace with the cover off. The burner lit every time but if I let the burner burn for a while it will suddenly shut down, this does not happen every time just most of the time. This A.M. it was 47 degrees and the furnace stayed on until I turned it off, after the trailer was warm. I am at a loss to understand what is wrong with the darn thing. Help??????

Conrad Holsomback
mailto:triconholsomback@greenwood.net

By Tripp, George on Wednesday, September 01, 1999 - 04:33 pm:

Conrad:

From what you say about the furnace, I would check two things. First, I am surprised that the furnace will run at all with the cover off. Most furnaces have a sail or pressure switch to ensure that the air is being circulated before they will stay lit. Second, if the furnace stays on after the temperature is reached, the thermostat may be faulty; however, the fan is supposed to keep blowing until the furnace temperature comes down...another safety feature.
I hope this is helpful.
george


George Tripp
Co-ordinator
General Studies for Technology
Fanshawe College

By Jim Dunmyer on Wednesday, September 01, 1999 - 04:34 pm:

Conrad,
I'm lucky, my furnace has no electrical gadgets on it. [grin]

However, I'd guess that yours has a safety switch that is supposed to be made up when the blower is running to "prove" the air flow. I've seen furnaces use centrifugal switches on the motor shaft, and I've seen them use "paddle switches" in the combustion air stream. Look for one of those and I'll bet you'll find your problem.

If they use a paddle switch, something blocking the air flow could cause a failure such as yours, even though the blower is running. (wasp nest, etc.)

Jim

By AirStremer@aol.com on Wednesday, September 01, 1999 - 04:35 pm:

Hi, Conrad....

I have the same furnace..and had the same problem. As someone mentioned it is probably the "sail" switch...this is the switch that must be turned by the blowing air before the ignition will come on. Sounds like it is sticking just a little. Might give it a look see... Not sure exactly how to get to it because I didn't know enough at that time to have a clue..and had to have a RV repairman fix it....must not be too hard...took him about 10 minutes..and it took be for $65! LOL Good luck

Phil
Scottsdale

By Bruce Levitt on Wednesday, September 01, 1999 - 04:36 pm:

I have the model NT-30S Surburban Furnace, and I have the Airstream service manual that includes furnace troubleshooting. There is about four pages of trouble shooting regarding the problem that you describe. IMHO it would be in your best interest to purchase the service manual for your furnace, or take it to a certified repair center. Personally after reading the service manual I would let a professional look at it. The electronic ignition system is sophisticated and performs four functions it doesn't just light the furnace it looks at specific operating parameters and will prevent the furnace from operating and will shut it down if it sees a failure. It appears that your furnace is going into a lockout condition where the spark fails to light the burner. The gas valve closes and the blower continues to run until the thermostat is turned off. There are an additional 28 steps in the service manual to go over to determine this cause of failure. If you are determined to fix this one yourself you are going to need the service manual for this one !
Good Luck

By Dave Wanamaker on Saturday, October 23, 1999 - 06:26 am:

We have a 1979 31' International that we just purchased this summer. We tried to get the furnace going last weekend in preparation for camping this weekend but each time that we tried we blew a fuse. When we turned the temperature up to start the blower it would blow a 20 amp fuse. I believe that there must be a short somewhere but do not know where to start or what to look for. Does anyone have any ideas for me? So far we have really enjoyed the trailer and everything else seems to work just fine. I look forward to your responses!

By Randy Hoops on Saturday, October 23, 1999 - 06:28 am:

A fan motor should require quite a bit less than 20 A, so there is either a wiring short or a "stalled" motor, perhaps with frozen bearings. If you can get to the fan see if you can turn it by hand. If you can't turn the fan motor is the problem. Does the motor run for a short time before blowing the fuse, or does the fan never move?

By Dave Wanamaker on Saturday, October 23, 1999 - 06:29 am:

The fan motor does not start. The fuse blows immediately after turning up the temperature to start the motor. I will try to get at the motor to see if I can turn it by hand.
Thanks so much for your help!!

Dave

By Dave Wanamaker on Saturday, October 23, 1999 - 06:30 am:

I just checked the fan motor and I can spin it with no problem. I reached in inside the little closet which runs under the counter behind the furnace access cover. There is a blue wire with a white cap on the end of ot that is comming out from the top of the fan ( over top of the metal housing) that seems connected at the one end but is obviously not connected at the other end. Could this be part of the problem? I pulled gently on it and it is connected to something but I could not see without taking things apart.
Thanks again,

Dave

By vcomunale on Wednesday, January 19, 2000 - 04:48 am:

When I light the pilot for the furnace on my recently purchased 1973 Overlander it just backfires and won't get going.

I'm following the instructions to:

1. set the thermostat at lowest setting (not off)
2. opening the gas line hand valve
3. depressing the reset button
4. lighting pilot (it usually lights ok until all goes PUFF!)

Does anyone have any suggestions before I have to call a professional?

Thanks, Vince

By Tripp, George on Wednesday, January 19, 2000 - 04:49 am:

Hi Vince:

I am not a furnace professional, but I do have a couple of suggestions. First, if the pilot lights and stays lit until the thermostat calls for heat, the thermocouple appears to be ok. Thermocouples are the biggest problem with pilots that go out. Second, if the pilot stays on until the gas ignites, I suspect dirt. The dust that flies from the small whoosh (tech term) when the burner ignites blows out the pilot. Often

One encounters this problem when a furnace has been sitting idle for a time. The fine rust particles start to circulate, and bam!. Clean things up really well with a soft wire brush and a vacuum and see what happens. Good luck!

george

By Bill Brackett on Wednesday, January 19, 2000 - 04:50 am:

Hi Vince.

Had trouble with mine the 1st time I used it, and the water heater too. The small gas line to the pilot was leaking at the valve, only when the unit was hot. With the heater a small quantity of gas would usually accumulate in the bottom of the firebox and ignite when the furnace cycled on, putting the pilot out when it tried to start.

One chilly morning when I was twisted up half naked in front of the furnace, trying to find the problem, a grapefruit sized ball of fire rolled through the kitchen and bedroom. It's funny now, but I almost got a triple hernia getting up and trying to grab the fire extinguisher. The line can be tightened with a small crows foot wrench on an extension. I use a discarded (contact lens) saline solution bottle filled with soapy water to check and recheck connections. The shop manual has list of other reasons the furnace might go out.
Hope this helped.
Bill

By vcomunale on Wednesday, January 19, 2000 - 04:52 am:

I Thank those that have responded to my request for suggestions in trying to get my Suburban Furnace going. After blowing out a lot of dust, hornet nests and other misc.. debris the pilot remained lit and a tubular "burner log" ignited. However, after trying several thermostat settings the blower only comes on when it wants to. Then it only stays going for a few seconds.

It would be helpful if I had a manual or some sort of trouble shooting instructions. It's an old model NT 32 A no longer in production.

Vince

By Tripp, George on Wednesday, January 19, 2000 - 04:52 am:

Vince:

I am assuming that the burner stays lit and the only problem is the blower. I do not know about the model numbers, but most of the furnaces have either a sail or pressure switch that controls the fan, in addition to a low/high limit switch. First, I would make sure that the furnace compartments are all CLOSED so that the proper pressure can build up. Next, does the blower make funny noises? Third, if you can find the low limit switch, check the settings. You may also want to remove the low limit and clean the sensor probe.

Good luck!

george

By Chris Bryant on Wednesday, January 19, 2000 - 04:54 am:

Obviously, my e-mail program doesn't deal well with styled text.. but... I *strongly* advise you to get a professional opinion- due to the age of this furnace, you could really be risking your life. This furnace had a recall on it to replace the "crossover" tube in it- it was probably done, but I still see those that were not.

The burner is cast iron, and is certainly fully clogged by now- the whole thing should have a thorough cleaning, and a close inspection for holes in the combustion chamber.

I'm kind of torn- on one hand, I really enjoy fixing old things and keeping them going, on the other hand, even if I was doing this for myself, I would probably scrap a furnace this old- after all, you only have one life to give to your Airstream ;-)

P.S.- I *really* want to discourage you from doing this- simply because you can spend many, many hours repairing and cleaning this furnace, only to have an unavailable part go bad (been there, done that), but if you insist, I may be able to dig up the service manual for it... but I *really* do not want too :-)

By Richard Keppler on Wednesday, January 19, 2000 - 04:56 am:

I'll third this for sure!

This spring, I had some problems with the furnace in my '74 SS. Dutifully took it apart, fully inteding to 'fix' it and noticed that the combustion chamber / burner had a hole in it that I could put my pinky through. I immediately decided to retire the complete unit and put in a new one. In the process of removal, I also noted that the exhaust tube had come loose and was sitting fully 1/2 an inch away from the port on the back of the furnace. This I wouldn't have seen had I not been removing the furnace! Why the CO detector hadn't gone off prior to this I don't know.

It was a bit of work putting in the new unit since the suburban furnace has changed somewhat, with the exhast/outside air port is at a different location. The bottom hot air vent requires that you get the extra parts to modify the placement. I took the hard way out and made all my own mating parts rather than order the ones I needed and wait for their eventual arrival. I also had to modify the skin to place the exhast port at the proper location which meant cutting a skin patch with properly placed holes and patching the skin. Used olympic rivets to attach the skin patch with polyurethane seal under the edge of the patch and old skin. Hand hand filed the rivet heads after trimming first with side cutters. Skin patch looks 'factory' and new furnace was in place and running perfectly less than 24 hours later.

By Tom Mosca on Wednesday, January 19, 2000 - 04:57 am:

The combustion products of propane are mostly CO2 and H2O; very little CO is produced. That doesn't mean that your situation couldn't have been dangereous. CO2 can cause suffocation if there's not enough air circulation.

Take care, Tom

By Richard P. Kenan on Wednesday, January 19, 2000 - 05:00 am:

The combustion products of propane are mostly CO2 and H2O; very little CO is produced. That doesn't mean that your situation couldn't have been dangereous. CO2 can cause suffocation if there's not enough air circulation.

This is perfectly correct, of course. However, the comment "very little CO is produced" may mislead some into thinking CO protection is not important - it is. Very little CO is produced *when* the burner is correctly adjusted. CO production rises with incorrect adjustment, and, being cumulative, can cause illness and/or death. I can recall that every winter in Columbus, OH, there were a number (more than 2) of cases of people killed by CO from propane space heaters that were not vented nor adjusted correctly.

CO2 can not only cause suffocation - it's also a poisonous gas when in sufficient concentration. That was a serious problem in the older submarines, when they had to stay down a long time.

Bottom line: Beware of CO, CO2, reduced oxygen, etc. Keep your trailer ventillated when using any kind of heater.

- Dick
(5368)
Dick Kenan
WBCCI # 5368 23' 1972 LY Safari
Atlanta

By vcomunale on Wednesday, January 19, 2000 - 05:01 am:

My thanks again to George, Cris, and others who responded to my furnace problems. I really had to explore the possibility of repair before thinking of dishing out quite a chunk of change. The new furnace I ordered today should keep me above room temperature in two ways!

Vince