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Old 10-10-2008, 11:09 AM   #1
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Suburban furnace where to start?

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
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Old 10-10-2008, 11:20 AM   #2
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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.
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Old 10-10-2008, 12:57 PM   #3
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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.
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Old 10-10-2008, 01:40 PM   #4
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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....
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Old 10-10-2008, 01:44 PM   #5
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I keep forgetting the high limit switch, that is a possibility.
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Old 10-10-2008, 05:09 PM   #6
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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.
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Old 10-10-2008, 06:56 PM   #7
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Quote:
Originally Posted by Leipper View Post
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.
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Old 10-10-2008, 09:09 PM   #8
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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.
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Old 10-10-2008, 09:36 PM   #9
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Quote:
Originally Posted by Leipper View Post
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?
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Old 10-12-2008, 09:44 PM   #10
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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
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Old 10-13-2008, 08:32 AM   #11
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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.
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Old 10-13-2008, 12:23 PM   #12
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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.
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Old 11-16-2008, 11:19 AM   #13
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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.
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Old 11-16-2008, 11:52 AM   #14
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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.
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