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perryg114 · 11-05-2011, 11:52 AM

Well I finally got around to trying lighting the furnace and the blower runs but it won't light. It is a Suburban made in 81. The components look ok. I am not hearing a ticking noise of the igniter. Anyone have any ideas where to start? Also the little access plate with the igniter in it looks like the gasket is asbestos. Does anyone know when they stopped using asbestos on these things?

Perry

Lumatic · 11-05-2011, 12:24 PM

It could be any number of things. I would start with the thermocouple. Then check the sail switch and limit switch.

handn · 11-05-2011, 02:08 PM

Is the trailer new to you? Do you know the history of the furnace? If it has been in the trailer for 30 years I would get a new furnace as the plenum is likely burned out.
I am reasonably handy but a 30 year old furnace is one of the DIY things I wouldn't touch.

perryg114 · 11-05-2011, 03:31 PM

If I can't get it to work I won't replace it right now. The plenum looks good but I plan on checking it for leaks once I get it running. It does not look like it has been used much based on the level of corrosion. I plan on using it to get a cold trailer warm then switch to an electric space heater or the heater coils in the AC unit.

Perry

Lumatic · 11-05-2011, 04:42 PM

Quote:

Originally Posted by handn

I am reasonably handy but a 30 year old furnace is one of the DIY things I wouldn't touch.

I agree, you are probably better off just replacing the unit. If you don't know about furnaces you will spend hours figuring it out and may end up with a furnace that kind of works and is kind of safe.

How about having a RV tech take a look at it. But make sure he knows what he is talking about.

lewster · 11-05-2011, 05:00 PM

Good luck finding an RV tech willing to take the responsibility for the continued safe operation of a 30+ year old furnace.......REGARDLESS OF IT'S APPARENT CONDITION! I wouldn't touch it!

For your own safety and piece of mind, I would not even consider trying to get it operational unless you want to remove it to the bench and use it as an educational experience.

You should replace it with a new, DSI (direct s[ark ignition) furnace that will give you years of safe, reliable service, not to mention that 'peace of mind' factor that you just can't put a value on.

It's your trailer and your life and you can certainly do as you please, but you did ask for opinions, and you now have my 'professional opinion'. Use it for what you will. YMMV!

Lumatic · 11-05-2011, 05:11 PM

Quote:

Originally Posted by lewster

Good luck finding an RV tech willing to take the responsibility for the continued safe operation of a 30+ year old furnace.......REGARDLESS OF IT'S APPARENT CONDITION!

Lewster is right. Qualified techs willing to put their name on an old furnace are few and far between. Unqualified techs? Now that's another story.

YMMV??

perryg114 · 11-05-2011, 05:24 PM

You guys act like these things are rocket science. It is a simple machine. Just about anything can be fixed and some things are not worth the effort. If it is not worth fixing I will figure that out. I am not about to risk my life or my family with something that is unsafe. If nothing else I will learn how these things operate.

Perry

Airline · 11-05-2011, 05:48 PM

Its not rocket science until it Explodes......

Lumatic · 11-05-2011, 06:48 PM

Quote:

Originally Posted by perryg114

You guys act like these things are rocket science. It is a simple machine. Just about anything can be fixed and some things are not worth the effort. If it is not worth fixing I will figure that out. I am not about to risk my life or my family with something that is unsafe. If nothing else I will learn how these things operate.

Perry

Not as complicated for me as a computer (which for some are not) but more complicated than a toaster. 5 years ago you would have been reading my mind. Now I know enough about how the furnace works to be semi-dangerous and wish I just bit the bullet 5 years ago and got the new furnace (which I had to do anyway). Using 20/20 hindsight I would have been better off if I took that all time and learned to play the accordian.

perryg114 · 11-05-2011, 08:46 PM

It is not an item that I can't live without. It just gives me more heating options. I expect it is the sail switch because nothing it coming other than the fan motor. According to the service manual, the first event it that the motor comes up to speed and that sail switch enables the start sequence. The gas valve opens and the ignitor starts and after 15 seconds or so it turns the gas valve off if it does not get a signal from the thermocouple. Since none of this is happening, then the sail switch is probably the culprit or the control board.

Perry

mopariac · 11-05-2011, 09:04 PM

Wow...people that love vintage Airstreams, but not liking old appliances. I gave my 40 year old furnace a chance and found dobber nests in both the intake and the exhaust. I cleaned them out and it runs like new. I am not made of money so a new one was out of the question and I don't need some handyman rv tech to learn my new old appliance system for pay (I need to know how they work).
I don't know about yours, but my suburban will turn the fan on at the thermostat just by raising the temp. However, in order to light the furnace, the temp has to be set on the coolest setting before the pilot can be lit. Once the pilot is lit, raise the temp and walla...the furnace prrs like a summer dream. Hope this helps and good luck!!

Tharon

4RXLA · 11-05-2011, 09:07 PM

Perry, FWIW the original furnace in my 77 works great and gets serviced regularly.

perryg114 · 11-06-2011, 05:44 AM

Well I do understand where they are coming from. If you don't know what you are doing and you don't pay attention you can get hurt. CO poisoning is probably the biggest problem to worry about. If you can smell propane when the furnance is running chances are you have a leak in the heat exchanger. It is always a good idea to have a CO detector when running gas appliances.

Perry

perryg114 · 11-08-2011, 07:58 AM

Well I am beggining to feel stupid. I think the problem is that there is a gas shutoff valve under the trailer that is in the off position. I won't know till I get home but that would explain a lot.

The sail switch is good. The control board is good. The thermal overheat switch is good. It looks like there is no gas supply. I seem to remember a valve in an odd place under the skin. I bet it is off.

I took the board to an electronics buddy of mine and we put it on the bench and it works just like it should. It sparks for a few seconds with the gas solenoid open and then it shuts everything down. The good thing is that I know it works like it is supposed to when I get it running.

So maybe all you nay sayers were worried about nothing. How many RV places would have just put a new one in there and charged me $1000 and grinned ear to ear the whole time.

Perry

perryg114 · 11-08-2011, 06:34 PM

WARNING you are about gain knowledge of evil. Don't bite the apple or swallow the pill because you will never being the same. If you wish to stay in blissfull ignorance don't read further.

Well after putting the control board back in and still having problems the control board is flakey. I got it to start once. It is supposed to open the solenoid valve and run the sparker for several seconds and if it senses a signal from the sense lead that is the small wire next to the spark plug wire it continues to run otherwise it shuts down. The sense leads is not a thermocouple but a voltage source. When 12V goes to the gas solenoid it also sends 12V to the sense lead. The control card measures the current to ground and when it senses a current it keeps things running. Current flows when the air becomes ionized by the flame and becomes conductive. When mine started everything worked like it is supposed to and the fan ran while the furnace was hot even after turning the thermostat off as it should.

It appears that the circuit that tells it when to start is messed up. This circuit is supposed to wait a few mins after shutdown before it lets you start back up again.

The board is supposed to go through a cold start sequence as soon as the fan motor is up to speed and the sail switch closes and sends 12V to the card. There is also a thermal switch in series with the sail switch. The thermal switch is on the front face of the control board housing. I could measure 12V on the input of the control card but it would not initiate the start sequence.

Perry