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Pacerized · 10-10-2008, 10:09 AM

My 1981 exella's suburban furnace won't ignite. The thermostat seems to be working properly in that it makes the blower motor kick on when I set it to a temperature higher then that of the air temp in the airstream. I have an early circuit board on the furnace that I see nothing obviously wrong with. The furnace has a 2 post igniter instead of a pilot light. I'm not sure if it's a spark igniter or a heated ceramic igniter like the one in my house. I would have no idea how to test the circuit board. Would a logical first step be to replace the igniter? If not where should I start to diagnose this?

Thanks: Charlie

HowieE · 10-10-2008, 10:20 AM

Before getting into the electronics check one thing. I have found that if my gas system has been opened and gas pressure relieved in the lines that the heater will not come on because of air in the lines. What I have done to correct this is brake the gas connection at the heater just until you smell gas. This insures you have gas not air at the heater. Then tighten the connection and cycle the heater.

If everything is working the fan should come on for about 15 to 20 seconds and then you should hear the gas solenoid click and the heater start to put out heat.

The reason for this problem of air in the lines is the fact that the pilot valve in the heater is so small that it can not purge the air in the lines in the time allowed for proof of pilot flame and thus denies turn on.

Mike Leary · 10-10-2008, 11:57 AM

Replace the ceramic ignitor, it's cheap and you can do it yourself. Make sure the kit has the gaskets. Suburban is notorious for their crummy heater motors & cards. Should it be a card, get one from Dinosaur. The furnace will have to come out for the card, but it should need a good cleaning and inspection given it's age anyway.Dinosaur Electronics Home. High quality circuit boards for RV appliances.

purman · 10-10-2008, 12:40 PM

Mine did the same thing, fan worked but wouldn't start Cost me $60 to get if fixed... Was a switch, that clicks to let the burning know the fan is on... WORTH is for me as the whole thing is electronic....

Mike Leary · 10-10-2008, 12:44 PM

I keep forgetting the high limit switch, that is a possibility.

bryanl · 10-10-2008, 04:09 PM

one of the best ideas I have seen to start furnance diagnostics is from Chris who has an entry about the first thing he does to figure out furnace problems. Short the thermostat with an ammeter and you can see each step of the start up process.

Mike Leary · 10-10-2008, 05:56 PM

Quote:

Originally Posted by Leipper

one of the worst ideas I have seen to start furnance diagnostics is from Chris who has an entry about the first thing he does to figure out furnace problems. Short the thermostat with an ammeter and you can see each step of the start up process.

I agree; take the coach to someone who does this every day, pull the furnace.
I bet most of you guys have the original; we're on our second & # 3 motor.

bryanl · 10-10-2008, 08:09 PM

Oh boy, another judgmental argumentative intentional distortion of quotations thingy - I just love that Airforums 'tude (pse pardon my sarcasm).

I provided a link from an experienced tech that provided the rationale and reason, qualified it as a place to start, and get such a response: No rationale, no reason, just presenting a false quote and being argumentative. I mean, like, what's the deal here?

You might want to see if Dave can provide the story about how we replaced a motor bearing on a blustery Pyramid Lake weekend with a silicone sealant nozzle cutout. That was near 20 years ago and we've been having furnace fun with old Airstreams since. We've even encountered overheating problems due to inadequate airflow. I agree with the Dinosaur board quality idea if your control board is suffering.

Pulling the furnace is a royal pain in most of the rigs I have encountered. It is good to have an idea that it is really necessary before doing that just as a matter of course. That is why I offered the suggestion. Watching the current draw can also help you understand how the furnace works which, in turn can help you debug and diagnose problems if you do have to pull it.

Mike Leary · 10-10-2008, 08:36 PM

Quote:

Originally Posted by Leipper

Pyramid Lake

Nice area! By the way, we've only had four Airstreams in the past forty years
and know a tad about them. Loosen up, pal, is the blue beret on backwards?

Pacerized · 10-12-2008, 08:44 PM

Thanks everyone for the input so far. Unfortunately I haven't had a day off to work on it yet. We did get our first snow of the year last night which required me to find the time to winterize. I think I'm going to check the gas line first as suggested then take the igniter out to bring to our local hvac store and see if they have a way of testing it or if they have one in stock. My igniter mounts on a plate that has 2 post with a wire running to each. Would one of these wires run to the limit switch that was brought up?
By the way the unit I have is a Suburban nt24m 24000 btu model. It looks like the igniter with electrode runs around $25 online.

Charlie

HowieE · 10-13-2008, 07:32 AM

Post #7 on the thread
http://www.airforums.com/forums/f37/...ign-29394.html
Is your wiring dia.

If you have that Fan Switch notes down by the motor you can proof the Sail and Limit Switches by reading continuity between the Brown wire coming from to one side of the Sail Sw. and the Red wire going to the Board from the Limit Sw
Attach your ohm meter to these wires, push a straight pin into the wire as an attachment point, and manually turn on the Fan Sw. If when the fan motor starts you see continuity you have proofed these 2 parts. Just make sure you get to the right side of the sail switch. You will see continuity before starting the Fan Sw. if you are on the wrong side, reading just across the Limit Sw.

On a small chance you do not have continuity in either case put the pin through the other Brown wire and check again. This will be just across the Limit Sw. and if that also reads No conitinuity the limit Sw. is open.

My bet is still on the gas line.

HiHoAgRV · 10-13-2008, 11:23 AM

The only problem I've had that caused a no-light (besides the air bubble that Howie covered) was low voltage. The Battery was a full 13+ volts but at the furnace with the fan-a-spiinin' I had 11.8 - apparently not enough to pull in the gas solenoids. A bad crimp at the furnace connector was the culprit, been runnin' fine ever since.

Jim in Pima · 11-16-2008, 10:19 AM

Hmmm, everone seems to have missed LISTEN. Turn up the thermostat til you hear it click, run over to the furnace..blower comes on, then after a moment ?CLICK again, the relay, then after a second ZAP, the ignition. If it ZAPS again and again, no gas. Tear outside and check the exhaust, is it warm,?? smell of gas?? blowing a good breeze???
Often this solves the problem
ps just solved a clogged gas line tis way.

bryanl · 11-16-2008, 10:52 AM

Quote:

Turn up the thermostat til you hear it click, run over to the furnace..blower comes on, then after a moment ?CLICK again, the relay, then after a second ZAP, the ignition. If it ZAPS again and again, no gas. Tear outside and check the exhaust, is it warm,?? smell of gas?? blowing a good breeze???

Good advice. I suggested doing essentially the same thing with an ammeter to assist but got flamed. Wish these forums were more receptive to ideas in a positive manner.

HowieE · 11-16-2008, 01:47 PM

Quote:

Originally Posted by HowieE

Before getting into the electronics check one thing. I have found that if my gas system has been opened and gas pressure relieved in the lines that the heater will not come on because of air in the lines. What I have done to correct this is brake the gas connection at the heater just until you smell gas. This insures you have gas not air at the heater. Then tighten the connection and cycle the heater.

If everything is working the fan should come on for about 15 to 20 seconds and then you should hear the gas solenoid click and the heater start to put out heat.

The reason for this problem of air in the lines is the fact that the pilot valve in the heater is so small that it can not purge the air in the lines in the time allowed for proof of pilot flame and thus denies turn on.

Well it is a good thing I just posted this solution because I had no heat Friday night and had to get it fixed ASAP because it was cold. Had to brake the gas line connection Saturday am to purge the air from the line and then the heater worked fine.

If you want to tare into the heater before verifying that you have gas at the heater have at it but I have found that cars, trucks, and heaters need gas before all else.

Pacerized · 11-17-2008, 07:57 AM

Just a quick update on my project. After I posted the first thread where as my furnace had stopped working on our last trip to Moab winter set in quickly here in the mountains. My time is very limited due to work so I had to stop working on the furnace and quickly winterize the Airstream. We were then given a nice reprieve in the temperature so I decided I'd better spend the time I needed to in staining my house and coating my driveway before the real snow started.
Back to the Airstream, I determined that I wasn't getting a spark by listening and trying my multimeter so I replaced the starter with diode since it was cheap. I only hear the blower motor start and then nothing else. This wasn't the problem so I started to take off the gas line as suggested but found it to be a very difficult task. I've given as much torque as I feel comfortable with and just can't get the line to break loose. Any more and I'm sure I'll just break the line. I've been trying to work on the furnace without pulling it out but may need to do so after all.
Everything that is in line after the furnace lights fine with the gas. Wouldn't that rule out a lack of fuel at the furnace?
I haven't been able to locate the sail switch. Could someone tell me where this is usually located? I thought I'd start with that and then test everything that I can with my multimeter starting with the limit switch.

Thanks: Charlie

HowieE · 11-17-2008, 08:55 AM

The sail switch is buried deep inside by the fan. You have to remove the Sub to get to it.

Yes a flared fitting can be hard to brake free. If you can get a wrench on the flare nut and one on the shut off valve you will be able to open thet connection.

Like I mentioned above I have to open mine Saturday am.

I don't know of any other way to purge the gas line to prove that you have gas at the burner.

thenewkid64 · 11-17-2008, 09:29 AM

I had to replace the sail switch in mine years ago, it has to come out to do it.

So you have fan, but no second click?

The order of operation is:

Relay click , Blower motor start

Sail switch closes

Gas valve opens (audible click)

Ignition (audible clicking)

Heat!

So if the sail switch is bad, the furnace will never light. If you have gas at the appliances down stream, I doubt gas is the issue. Do you hear the clicks as outlined above? If not the sail switch is the logical culprit, and while it is a PIA to replace it is less than 20 bucks to get...

HowieE · 11-17-2008, 11:05 AM

I think I am having a little problem making my point here. The fact that you have gas down stream dose not mean the heater will light.

The main gas valve on the heater will only come on after there is PROOF OF PILOT. If there is air in the line the pilot valve is too small to bleed off the air in the time allowed for proof of pilot and the cycle will just time out.

Jim in Pima · 11-18-2008, 08:33 AM

Couple of comments, sail switch, I have helped several check these out, usually the cause is dirt in the switch, or restricted air flow, either a slow blower, or something blocking the input air (both combustion air or heater air can cause this.) Poor DC connection can do it as well, check these before pulling the furnace
Gas flow, I just went through that, old furnace had not been used in years, I found the line leading to the shutoff valve (under the trailer) was completely blocked, reamed it out with a heavy wire.
No idea what caused it, perhaps moisture at some point.