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Paul Daugherty · 02-09-2003, 06:50 PM

My furnace heats well but when it is below 40 degrees the fan just runs and runs. The thermastat has been replaced. It seems to run to long after the flame is out. When it cycles the furnace goes on and off but the fan keeps running. This is a suburban furnace in a 84 Airstream. Any one ever take one apart and fix it themselfs.
Paul D...

evan · 02-10-2003, 09:43 PM

I had this same problem with the furnace in a AS trailer. It turned out to be a bad circuit board that had to be replaced. The circuit board controls a complex series of feedbacks and switches between thermostat, the fan motor, sensors etc. The fan also purges the the combustion chamber of unspent gas before it shuts down. Purhaps you have a bad gas valve or the flame sensor is bad? Also check the fan relay, it could be sticking. Good luck.

wb13798 · 02-11-2003, 08:28 PM

had the same problem last year. replaced the lower limit switch/sensor and cleared the problem. take the front cover off it is on the bottom right . push on it and it will click. probably sticking. the furnace has to run for a while to cool down the the burner chamber then cuts the blower off. lol
al

wb13798 · 02-11-2003, 08:41 PM

paul
i will post a jpg tomorrow for you it is probably sticking and clicking may clear that problem it did on mine but i replacef the switch any way. to click just push in till it clicks. mine got soo bad it only would malfunction at 2 in the morning and it was blowing cold air. this temp sensitive switch turns the blower motor off.
al

wb13798 · 02-12-2003, 08:54 PM

paul
sorry but thw digital is on the blink. do you have a manual ??? if not TAKE THE FRONT COVER AND look on the lower right and you will see a silver crome looks like a button push and you will hear a lick that iS the switch. if it still doesnt cut the blower OFF.on the cool down cycle in a reasonaBLE TIME REPLACE IT. IT IS NOT A HIGH DOLLAR PART. it is a pain in the --- to replac. the god part is you dont have to remove the furnace. lol
al

Paul Daugherty · 02-13-2003, 03:05 PM

I don't think I have the same thing or type of furnace. I will send a picture today if I can. Thanks for the help

Paul Daugherty.

Paul Daugherty · 02-13-2003, 03:21 PM

Here is a pic of my furnace. I do you have the same kind and year.
Paul

Sorry I can't figure out how to send a pic in this forum I need Help
Paul

wb13798 · 02-13-2003, 04:53 PM

paul
are you going to mystic springs??? i have a suburban nt-30sp . and that is the furnace that airstream put in everything that was close to 30 ft. im planning on going and if you are there ill put my finger on it.. and click it.. lol al

to post a picture go to attach file (below/options) and click on browse and a window (my computer/documents) should come up for you to select and identify the picture file. below the brousetab . list the files that the server will accept. hope that helps.

Paul Daugherty · 02-13-2003, 05:12 PM

Its an 82 not an 84 AS. My mistake

wb13798 · 02-14-2003, 05:17 PM

ok looks like mine. on the left side above the wire connection is the sight glass for looking at the flame. on the right side above the gas line is a switch (looks like another sight glass) not so it is the switch i have been telling you about push it it should click if it doesnt dont worry just wait untill you use the furnace again and see if it made a difference if it didnt open the door again while it is warm not hot and push it again. mine is cold and wont click i think it has to be warm to click . in any case you have unstuck if it was stuck. next question when the blower is running is the air warm or cold. if cold the switch is probably bad. if warm dont worry about it. be happy. lol
al

ALANSD · 02-14-2003, 09:01 PM

I have the same furnace. Another thing to look at is the color of the flame, to be sure it is getting enough air. It should be nice a blue when you look thru the site glass or in from the outside of the motorhome. If it is too orange or yellow, the air vlave on the side needs adjustment. It screws in and out. Also i was advised to clean out the air intake tube really well from the outside to be sure it isn't blocking the air flow. Mine has a new igniter, but the air adjustment is now in as far as it will go and although the flame is mostly blue...I have no adjustment left.
Also there was a good thread here on checking your gas pressure to be sure it is high enough.
The furnaces do get burnt inside the chamber and need cleaning, although I haven't yet attempted that one.

Paul Daugherty · 02-15-2003, 06:36 AM

I did check the flame it is nice and blue, but where is that adjustment screw you mentiond? I did clean the heat and gas exaust (the one on top). It had two mud dobber nests in it. The lower hole (air intake) Has a screen on it. From other post I have read that screen is not standard issue on a suburban furnace. Their web site does not recomend them. But if they don't recomend it then how do you keep the mud dobbers and other pest out? (Geroge is getting frustrated)

Paul....

ALANSD · 02-15-2003, 03:00 PM

if you pull off that little cover under and to the right of the wires the two screws come off....there is an adjustment inside there.

Larry Brown · 02-15-2003, 06:18 PM

I have the same unit it started to act the same . I did a cheak of all the components with an ohm meter and found an open coil on the relay.that fixed the problem for 1 year.the next season the furnace did the same thing again.I replaced the thermostat. it fixed the cycling again. But the problem came back .So I purchased a new circut board. Promblem solved ? tell next season .Than I called the R.V. gas appliance repair shop .For 30 bones they tested the whole system on test station and fixed the problem with a gaurantee.

primatreat · 02-15-2003, 06:52 PM

Had the same problem on 31' international..changed the switch, board,thermostat and it worked fine..Then at night would't work again.. cold air.. notice the fan was slower with the lights on.. I'm on hard 110v. I have a new gel deep cycle battery.. On a whim I put a charger on the battery.. worked like a charm.. Put in a new converter and my problems are over.. Upgrade your converter and most if not all of your problems will go away.

Paul Daugherty · 02-15-2003, 08:36 PM

Alansd,

I took another look at the color of the flame and there is some yellow. Which way do you turn that screw? Clockwise more air counter clockwise less air.
Early I was asked if I was going Mystic Springs II, Don't think so but you never know it all might come together.

As always you guys give great advise thanks,

Paul...

davidz71 · 02-17-2003, 12:13 PM

I had my NT30 rebuilt Feb. 2002 with a new motor, mud daubbers cleaned out of the combustion chamber, new circuit board and bench tested. I had pulled the unit out and taken it to the dealer. During the last year I noticed that while it always fired up after the first or second time, it would not refire after it had run for a period of time. No difference was noted between battery power or running plugged up to shorepower. I pulled the front cover off after taking out the lower tambour and aluminum trim. I turned the thermostat on, got my face down where I could see the combustion window and heard the fan turn on. Within 20 seconds the furnace fired up and a nice blue flame was evident. It cycled on and off without problems although the cabinet area was getting rather hot. I pulled the unit over to the RV dealer and he found that the thermo switch on the right side was not letting the unit fire up again because the inside was getting too hot with the cover on. Consequently, it overheated the new board he had put in on the rebuild. He replaced the thermo switch and a new board then blew out the furnace ductwork. He feels that there is a slight restriction toward the back area near the bathroom but could not find it. The furnace has 2 openings on the right side facing the front of the trailer. One had a plate on it which he removed so that there is more air moving toward the front of the trailer. All belly hoses were checked for kinks and found not to be restrictive. The unit seems to be working fine now but I will be removing the panel behind the commode to get a better look at the ductwork for a possible restriction.

ALANSD · 02-17-2003, 03:50 PM

turn the screw in tighter to increase the air flow. Watch the flame color as you do it. It should be as blue and even as you can get it. Mine is now all the way in, as i said, and that concerns me a bit, but since we don't camp as much in the colder weather, the heater has been effective when used.

Paul Daugherty · 02-18-2003, 03:15 PM

So can you do this adjustment when the furnace is running or is that not a good idea.
Paul..

ALANSD · 02-19-2003, 07:34 AM

yes - furnace running so you can watch the flame. No problem, just a bit warm around the base. I did it in the campground one afternoon, had the manual out and the long driver to get in there. It helped my heat at night when it seemed like it was running a bit too long. I went outside and looked at the flame from there also as it seemed to be easier to see what was going on.
there is some more info at this link

http://www.marksrv.com/furnace_trouble_shooting.htm