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wacnstac · 05-15-2006, 12:23 PM

What is puzzzling is that the ignitor is brand new and yes it is the exact correct replacement for this furnace. It matched the pattern and offsets of the old one exactly. The spark looked very healthy and was arcing down to where the burner is. Quite puzzling if you ask me.

john hd · 05-15-2006, 12:29 PM

wac

i'm beginning to think you are a glutton for punishment! (just kidding!)

do yourself a favor and just go get the dinosaur board and a new ignitor. not more than 150 bucks for both.

i just had to do this for my furnace, and it is only 1992 model! the stock suburban boards are failure prone period. follow lew's advice.

if you hate spending the money on a possibly good part don't worry, the dinosaur board is an aboulute upgrade! in addition to getting a mil spec circuit board that is double soldered. you also get diognostic l.e.d.s on the new one!

the new board i just installed has a green/red l.e.d. that shows green when power is present, then turns red when the gas valve is opened. there is also a neon light that shows the ignitor is firing. a helpfull feature when trouble shooting your furnace!

the best part is i can see the light from the l.e.d.s when the furnace is installed. if my furnace screws up again i can just look in the back of the cabinet and see what the boards status is by looking for red/green or neon.

oh, i almost forgot to mention the new board is a 3 try system with auto fan shutdown after 3 min.s a real battery saver!

john

john hd · 05-15-2006, 12:31 PM

on edit,

wac i did not see you got a new board!??? or the electrode??? perhaps you got a bad one out of the box!

sorry

john

wacnstac · 05-15-2006, 01:05 PM

I've already replaced the ignitor. Am thinking about the Dino board upgrade, but I wouldn't be able to see the leds on the board once it is installed.

john hd · 05-15-2006, 01:28 PM

wac

i cannot see mine directly. however, they are bright enough to illuminate the side of the cabinet.

john

75excella · 05-15-2006, 02:33 PM

Hello, I have the same problem with my furnace. it is the origanal 1975 NT32 model. After much research I suspect it is the limit swith. The furnace will go into lock out because the cabinet temperature gets too hot and the limit switch open up. This commonly occurs because the airflow can get restricted and cause the temp to rise. I found that if I remove the front panel and let the air come out the front the furnace work fine. I have not replaced my old switch yet but I suspect it is become a little weak and cuts off a a slighty lower temp than when it was new. I hope this helps - good luck.

wacnstac · 05-15-2006, 02:57 PM

Is the limit switch a replaceable part seperate from the ignitor control board? This would make some sense since when my furnace does run, it ocassionally turns the fan back on two or three times for short blasts presumably because it is detecting too high of a residual temperature in the cabinet area.

If I take this sucker out again it's getting a new board and I might as well replace the limit switch at the same time if it's available.

75excella · 05-15-2006, 03:04 PM

I believe so, it is a two prong switch that is attached to the cabinet with two screws, it lised on he schematic in series with the micro swich and the gas valve.

lewster · 05-15-2006, 05:46 PM

Quote:

Originally Posted by wacnstac

Is the limit switch a replaceable part seperate from the ignitor control board? This would make some sense since when my furnace does run, it ocassionally turns the fan back on two or three times for short blasts presumably because it is detecting too high of a residual temperature in the cabinet area.

If I take this sucker out again it's getting a new board and I might as well replace the limit switch at the same time if it's available.

Hey Wac,

Here's what I would do. First, I would get a new ECO (limit switch). It is easy to replace....just 2 screws on the plenum and 2 wires. Get a new sail switch. Just as easy ro replace. Then get a new Dinosaur Fan 50+ igniter board and you have essentially rebuilt the furnace and it should work great for a long time and it will shut down if the flame goes out and not keep running and blow cold air any more! Remember that the Dino boards are warrantied for 3 years.

If you have problems getting the parts, let me know and I can get them for you at the 'Forum price'

lewster · 05-15-2006, 05:49 PM

Quote:

Originally Posted by 75excella

Hello, I have the same problem with my furnace. it is the origanal 1975 NT32 model. After much research I suspect it is the limit swith. The furnace will go into lock out because the cabinet temperature gets too hot and the limit switch open up. This commonly occurs because the airflow can get restricted and cause the temp to rise. I found that if I remove the front panel and let the air come out the front the furnace work fine. I have not replaced my old switch yet but I suspect it is become a little weak and cuts off a a slighty lower temp than when it was new. I hope this helps - good luck.

75,

The situation that you describe is usually caused by a kink or obstruction in the ducting. I would check it thoroughly and also replace the ECO on your unit. Seems that it's been getting quite a work out!

wacnstac · 05-15-2006, 08:42 PM

I'm not afraid to spend the money on an ECU if I knew it would fix my problem, but at this point I'm not sure if it's that, the solenoid, or the limit switch or all of the above. If I replace them all, I might just as well buy a new furnace.

nickcrowhurst · 05-16-2006, 12:25 AM

Quote:

Originally Posted by wacnstac

I'm not afraid to spend the money on an ECU if I knew it would fix my problem, but at this point I'm not sure if it's that, the solenoid, or the limit switch or all of the above. If I replace them all, I might just as well buy a new furnace.

The limit switch should be easy to test without removing the furnace. On mine, it is a 1 inch diameter disc with securing lugs for 2 screws, and with spade terminals for 2 wires. It sits to the left of the furnace, low down, visible after a small plywood blanking piece is removed .The limit switch sits in the 12v power supply to the furnace, and when the temperature gets dangerously high, the switch opens, and the power to the furnace is cut. With a $5 multimeter set to its Ohms range on its lowest setting, or using the "beep" continuity test facility, you should see almost zero resistance between the spade terminals. When the furnace fails, do the same test. If you have infinite resistance, your limit switch is stopping the furnace from running. You should still find over 12 volts between the live terminal and ground, and zero volts between the other terminal and ground. You need to be precise with positioning the probes, so as not to cause a short.If, as I suspect, there is still continuity across the switch terminals, then the problem is not with the limit switch.

The sail switch can be tested with the same meter, but the furnace has to be withdrawn to do so. When at rest, there should be infinite resistance across the sail switch terminals. Blow on the sail or move it by hand, and the switch should close, showing zero resistance across the terminals. With the same meter, you can check the time delay relay while the furnace is out.

A healthy gas valve solenoid can be heard opening with a distinctive "click", just before ignition should occur. By listening carefully when the furnace starts correctly, you can learn how the "click" sounds, and hence help to diagnose a later failure.

On mine, as a matter of preventative maintenance, I changed the sail switch, limit switch, gas valve and time delay relay while the furnace was out to fix the cause of the problem, which was the circuit board. The old parts are stored for emergency repairs.The symptoms were identical to yours. I don't recall the figures, but it was a lot less money than buying a new furnace.

Nick.

wacnstac · 05-16-2006, 05:49 AM

Nickcrow where did you get all your parts from?

wacnstac · 05-16-2006, 06:39 AM

So you can see the limit switch by opening the little door behind the furnace that exposes the squirrel cage that's just to the left of the main entrance door to the trailer?

nickcrowhurst · 05-16-2006, 07:34 AM

I got the parts here http://www.sandersrvs.com/ Either Mr David Sanders or Chuck in the parts department have always done their best for me. This is a family business, of the best sort.
Your furnace may be installed differently to mine. On mine I get access to the front of the furnace by pulling off a decorative oak panel, at floor level. At the left hand end of the now visible front of the furnace is a piece of plywood about 2 inches wide by about 7 inches high. After two screws are removed, this piece of ply can be pulled away, exposing the limit switch and its associated wiring. The limit switch is screwed to the frame of the furnace.It doesn't look like a switch. It is a disc about 1 inch in diameter with two attachment lugs and two male spade connections for the two wires.
Nick.

75excella · 05-18-2006, 10:51 PM

Thanks for the e-mail Lew, that was the first thing I checked (air flow restrictions), and I did replace the furnace flex hoses. It my understanding that three outlets are the absolute minimum for the larger furnaces, and two of my outlets "T" into one. So I question the origanal ducting set up. I believe the furnace would run better with more airflow. I just have no easy way to add another duct on my 75 excela. It must have worked for several years as designed, so when I get around to it I will replace the swith before I mess with trying to improve the ducting airflow.

lewster · 05-19-2006, 07:41 AM

Quote:

Originally Posted by 75excella

Thanks for the e-mail Lew, that was the first thing I checked (air flow restrictions), and I did replace the furnace flex hoses. It my understanding that three outlets are the absolute minimum for the larger furnaces, and two of my outlets "T" into one. So I question the origanal ducting set up. I believe the furnace would run better with more airflow. I just have no easy way to add another duct on my 75 excela. It must have worked for several years as designed, so when I get around to it I will replace the swith before I mess with trying to improve the ducting airflow.

You're welcome.

It's interesting that the OEM's quite often don't read the furnace manufacturers' spec sheet concerning minimum # of ducts or square inches of output area. I have had a few cases where I had to add an extra vent (sometimes in a storage bay) to reach the required minimum duct area to keep the ECO from popping off.