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Old 01-02-2007, 08:48 PM   #15
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I'm also wondering if there might be something inside his combustion chamber that is causing the temps to get too hot and the temp limiter is kicking in?
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Old 01-02-2007, 09:23 PM   #16
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Quote:
Originally Posted by Marshall
I'm not quite ready to deep six it, actually having some fun tinkering. .... COULD IT BE SOME KIND OF BREAK DOWN IN THE COMBUSTION CHAMBER SEAL from the heat exchanger?
Yes, tinkering was fun for a while and when I got tired of the repetitious installation/removel routine I set the heater up to run on my bench for prolonged fun. I believe it's a NT-24 (yes I still ahve it in the basement). It has the evil bad seal between the blower and the combustion chamber and also what I suspect may be pin holes in the heat exchanger as well (which is no surprise since I did knock out a full cup of rust during my cleaning).

I am not feeling overly generous towards heaters since our home furnace began to intermittently quit while we were away this past weekend. It never got warmer than 62 yesterday and was a chilly 51 when we awoke this am. Our reliable tech replaced the igniter this afternoon and all is well tonight.

Sleep well,

Steve
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Old 01-02-2007, 10:05 PM   #17
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And when you're done tinkering, you'll still have a 30 year old furnace!
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Old 01-02-2007, 10:56 PM   #18
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Don't quit to early. If the furnace looks clean and neat, and the combustion chamber is solid (no rust, cracks, etc) all is not lost. The loss of flame is caused by 1 of 2 possible issues:

1. Fan "float switch" is faulty. This is simply a micro switch that has a paddle near the "squirrel cage" fan that insures that the main blower is indeed running. You can test the switch with a simple multi meter.

2. The aformentioned "roll out" temp sensor. This sensor tells the main board that the fire is to hot and "rolling out" of the combustion chamber. Simply watch the flame and assure that it is blue and totally over the burner. A multi meter test will show continuity to ground if tested after the flame has kicked out and this switch is the culprit.

After that it is probably the main circuit board. As the semi-conductors on this older board age they change values and move out of the operational parameters. My '81 model would turn on the fan but never light the gas. An inspection/cleaning and board change fixed all. The board is around $100.00 from Camping World or others, the Suburban kit number is 520741, the CW item number is 15388.
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Old 01-03-2007, 06:44 AM   #19
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Binder, et al:

Furnaces are basically simple units with a few safety controls on them, like sail switches, thermal overload sensors (ECO) and if you have a pilot light, a thermocouple. The first thing to do is be sure that all of the components are clean and free of obstructions from wasps and other insects. Be sure that all of the gaskets sealawhere needed and be sure that the burner chamber is sound. Also, clean the gas orifice with carb cleaner and NEVER put anything thru the opening as it is precision drilled!

Next, be sure that your gas valve is functioning by placing 12VDC across the terminals....you should hear a 'click' that indicates it is opening. Next, check the sail switch and ECO (high limit thermostat) for continuity. Next, check your thermocouple for proper operation. If you remove the leads and heat it, you should get a specific millilvolt reading when it gets hot. This functions to tell the PC board that the pilot IS on anad strong and that it is OK to open the gas valve. You can propaply find this spec on the Suburban web site, or PM me and I'll dig it up for you.

You can also have the board tested at ana well-equiped RV shop. If it is bad, you should replace it with a Dinosaur 'fan control' board which will do everything the OEM board does PLUS it will shut your fan off after a specified time if your furnace does not ignite after the programmed 3 tries.

PM me if you can't find these boards. They are the only boards that I use, and have a 3 year warranty! PM me or e-mail me (preferred) at: lew@gorge.net if you need further help or don't understand any of what is above.



Quote:
Originally Posted by SafeHarbor
Maybe RV Lew will chime in here, but there's a lock out switch that will shut off the gas if the temperature rise is too fast in the heater. This can caused by inadequate ducting of the heated air. The thermocouple will also sense an absent flame and turn the gas off. I think, but I'm not sure, that the board-equipped heaters turn on the spark before the gas turns on. Without the sparks, I doubt the board would LET the gas come on. Thus problems can occur with the lock-out switch (fan keeps running), the ignitor board (fan keeps running), and the gas switch itself (spark but no ignition and the fan keeps running). On the three heaters I've had, there's been a little circular window over the overheat switch. I don't know what it looks like if it activates.

My guess is that Binder should check his fuel supply, fuel pressure (11 inches of water), and then his gas switch. Oh, after a failed start, you should shut off the gas and run the fan for a while to clear the combustion chamber.

The NT-24 in my Argosy's favorite trick was to put out nice heat until I went to bed, and then flame out during the night. I''ve awakened more than once to a cold trailer with the fan blowing.

The board-equipped heaters can do it too.

Good luck with these things, guys.

Lamar
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Old 01-06-2007, 02:08 PM   #20
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Old Furnaces

I replaced my old NT22 with a NT20s. I think there was a recall on the NT22. In any case a 33+ year old heat exchanger just did no seem like a good idea to me. I plan on also installing a P9000 furnace one of these days. The 20s is smaller by 10% than the 22 but uses 50% of the 12volt power. The P9000 is also a light user. I did have to do a bit of cobbling, like a custom mount. I used angle iron --(grind the corners-you'll figure out why real quick!)-- to make a custom mount with a plywood deck that I screwed a metal face onto it. I was trying to post a photo but it is not taking I will try again later today.

Using an old furnace could be a risk. Make sure your monoxide and propane detectors are working---install some if you don't have them.
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Old 01-06-2007, 02:44 PM   #21
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I hope this worked/1
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Old 01-06-2007, 09:48 PM   #22
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I did something similar with an NT30. I used 7/8" plywood to "cobble" my new furnace into the original housing. (I did have to move it to the right about 3/4" to make the exhaust line up. Also had to cut a hole out of the side of the housing just like Smokin Camel. I lined the inside of the box with aluminum tape.

The first picture is in a '73 Sovereign. The other two were done in the '72 Overlander just before I sold it.
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Old 01-11-2007, 09:38 AM   #23
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Check the Alloy gas valve.

Hi from the UK,

My furnace has just come back from a service/repair. It worked at first but now will only blow cold. When I went back to the guy to ask what could be wrong he said that the inlet valve was sticking. Apparantly it's common. and due to lack of use. He recommended I give the side of the furnace a clout as the spark ignites to clear the sticking valve! He said he didn't have the valve in stock so he couldn't replace it.

Can you imagine me with a Flintsone type club resting against the kitchen wall ready for the time I want the furnace ignited? Or naked on the Gaucho because I don't dare turn the furnace off for fear it wont start again? Perhaps we shouldn't go there!


I wish he'd told me the extent of the problem before charging me $550 dollars just to replace the board. Replacing the valve will probably cost just as much if I can't beat the thing hard enough to get it started. So, that's a $1000 for a beaten up furnace! I could import a new one for less than $800. But, I guess he doesn't think that way! That wont make him any money!
At the end of all this he'll probably expect to sell me a new furnace... $1400

Marc
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Old 01-12-2007, 12:11 AM   #24
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Sitting on the gaucho naked is NICE if you have a catalytic heater churning out the BTU's (and that's British and thank you for converting to dollars) on the available flesh. However, if you have a cat behind you with natural curiousty and a tendency to poke things with a claw, prepare to say, "Ouch!" and have a one-sided discussion.

Lamar
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Old 01-12-2007, 04:04 AM   #25
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Lol!

In the words of Robin Williams, that's the moment you invent the Cat-a-pult!


Did you hear the difference between cats and dogs?

The dog thinks: I get everything from you, you must be a God!
The cat thinks: You give me everything, I must be a God!
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Old 01-25-2007, 02:57 PM   #26
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Gas Furnace won't remain lit.

I recently saw an article in the Blue Barrett that talked about using a tooth pick dipped in rubbing alcohol in the orifice of the gas line. This will assure the orifice is open enough to get adequate flow. I believe the alcohol does some dissolving at the point. I recently tried this on my '86 Sovreign and was successfil in getting it to light and run well.

Be careful not to distort the orifice; be gentle.

As far as the fan is concerned, there is a switch that requires the fan to show air flow before it will allow gas flow for ignition. You likely saw the switch while you were cleaning the unit. Check this switch and assure it functions well. Also, if the motor hasn't run in a long time, it will likely need lubrication if oil can be put on the bearings. If they are bad enough, it will cause a high resistance and likely shut the fan down or burn out the winding. Listen to it for smooth operation.

There is also a circuit that requires the fan to run for a time to clear the furnace after a burn. This can be a source of ignition failure.

Best regards, William_Mc
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Old 02-06-2007, 04:44 PM   #27
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NT22a Furnace update/71 Tradewind

Well, Suburban did recall this furnace because of a problem with the crossover tube disintegrating. Pulled the furnace and sure enough they were right. No service dealer in this area is willing to work on the furnace because of liability, but one told me what they used to do is put in a piece of auto gas tank filler hose. They said it is an easy repair and worth a shot.

I've gone this far so I think I will give it a wack (famous last words). At least it will be a learning experience. Will keep yall posted unless I blow up.
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Old 02-07-2007, 11:44 AM   #28
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Thumbs up

Quote:
Originally Posted by Marshall
...Will keep yall posted unless I blow up.
You won't blow up, CO is the silent killer

I'm not sure that gas tank hose is made to take the heat, but maybe it will work fine. Here is some hi-temp hose...

Another connection problem for me was the furnace exhaust. I think that it was fitted with some kind of asbestos rope packing around the connection to the outside cover.

Let us know how it goes,

Steve
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