OK, I just had a thought. I have not been paying attention to what the draft motor is doing. Maybe it's the source of all of this, dahhh. If the draft motor slows or gets intermittent it would cause the switch to misbehave. Bypassing the switch resolves this but the motor is probably still going to run erratically if it's the problem. I'll check next time I run the furnace.

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Originally Posted by KC13

If you jumpered NO to C and the unit sustains operation, that proves the switch was not maintaining the circuit. Make sure the switch circuit isn't breaking due to a problem with the combustion draft. The "flash" from the board? Likely the inducer relay arcing. If inducer operation becomes erratic this may be why.

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I had a feeling about this earlier, but you hadn't indicated that the motor was "sputtering". You had taken out the board that is housed behind the pressure switch before. The inducer motor relay is on this board, enclosed by a cubic-shaped cover. If you look closely and proceed carefully, you can remove this cover with a small screwdriver wedged under the tabs on the relay. I'd be willing to bet you will find the relay contacts burned. Carefully clean them with abrasive cloth and see if the motor runs more consistently. If so, the board should be replaced as a "permanent" solution. When you re-install the board, pay attention to the mounting tabs engaging into the housing properly. Afterward, give us a full report!

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Originally Posted by KC13

I had a feeling about this earlier, but you hadn't indicated that the motor was "sputtering". You had taken out the board that is housed behind the pressure switch before. The inducer motor relay is on this board, enclosed by a cubic-shaped cover. If you look closely and proceed carefully, you can remove this cover with a small screwdriver wedged under the tabs on the relay. I'd be willing to bet you will find the relay contacts burned. Carefully clean them with abrasive cloth and see if the motor runs more consistently. If so, the board should be replaced as a "permanent" solution. When you re-install the board, pay attention to the mounting tabs engaging into the housing properly. Good luck, afterward, give us a full report!

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For some reason this didn't post as most recent.

So I watched it run and the inductor fan ran smoothly. I also monitored the NO closed conncection and it remained NC. Pinching the silicone sensing line worked as expected, NC went to NO and NO went to NO on the meter.

I did have that board off but didn't realize the cover came off the relay. I'll pop it off and inspect. That is where I saw all the flashing when it cycles and just that might have damaged the contacts. I hope the motor is OK because it's not available and the replacement is expensive. I'll go check the contacts. I think I have a points file and contact cleaner.

Easy on the file! Don't wear off the contacts to the point that they don't meet firmly. I would prefer if you used some fine abrasive cloth. Cut a narrow strip and gently clean off contacts. This is not a typical service procedure but can get a unit running until the board can be replaced.

Guess I won't cancel the coffee shipment, lol. Boy those contacts are tiny. One side was blackened with lots of soot inside the cover. I used some fine 600 grit paper and contact cleaner and it fired right up. It's too warm for anymore testing so I'll give it go again tonight. Thanks again.

I feel confident that we have pinpointed the source of your problem, once and for all. If you end up replacing the board, the new one will likely come in a kit with some wires to add on. Follow the instructions and you'll do just fine. For someone who's not a "furnace man", you have done quite well with this. I'm so... (sniffle)... proud of you!:p

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Originally Posted by MarkwithaK

Let me repeat myself before those that praise the VS motor jump my back.

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Too late! We heard that and we're comin' for you!:D

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Originally Posted by KC13

Too late! We heard that and we're comin' for you!:D

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I have a catapult and a large stockpile of old dead motors... you'll never breach the perimeter.:)

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Originally Posted by KC13

I feel confident that we have pinpointed the source of your problem, once and for all. If you end up replacing the board, the new one will likely come in a kit with some wires to add on. Follow the instructions and you'll do just fine. For someone who's not a "furnace man", you have done quite well with this. I'm so... (sniffle)...proud of you!:p

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It just goes to show you that you even teach old engineers new tricks. And I didn't even blow up anything. I used to be a motorcycle mechanic years ago and I'm pretty used to working on things. I guess that's why I became a mechanical engineer. I found the board on eBay for about $98 and it's in City of Industry, CA. So I'll run it for awhile just to make sure. I see the new one has lots of extra circuitry like caps, probably to better protect the relay.

Given the age of this furnace, I'm concerned about some small flames I see coming out the sides of the burners when running. It's not a jet or anything but sort of a gently small candle size flame where the seams meet. The heat exchanger itself is in good shape. I'm sure there will be lots of good deals and rebates this year so if it lasts through our very mild heating season I might just replace it soon anyway.

Are the burners a long sword like design? Depending on where the flames are popping out they could be deteriorated.

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Originally Posted by MarkwithaK

Are the burners a long sword like design? Depending on where the flames are popping out they could be deteriorated.

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They're more like small horns, maybe 4-5 inches long, three of them. They look like a two piece design with the two halves split horizontally. That where the small "leaks" are and right at the end only where the flames exit.

[QUOTE=sdcruiser;1457578 Given the age of this furnace, I'm concerned about some small flames I see coming out the sides of the burners when running. It's not a jet or anything but sort of a gently small candle size flame where the seams meet. [/QUOTE] The crosslighters may be spread open a little wider than normal due to the age of the unit. They can be crimped down a little to reduce this condition, but don't overdo it or late ignition may result due to poor flame carry-over. Use a dime as a gauge.

I have yet to see a 21 year old system with in-shot burners. That's a new one on me.

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Originally Posted by MarkwithaK

I have yet to see a 21 year old system with in-shot burners. That's a new one on me.

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Not sure what in-shot means but I attached a pic. It's the first of the carrier 82% AFUE furnaces and the house was built in 1987. I'm the original owner.

One of the original Carriers and it is still running. Does it have the three wire pilot. If so that can give you a fit sometimes. They will allow the unit to run then drop out of the circuit at any time. The link is for some of the original specs on that unit.


http://www.xpedio.carrier.com/idc/gr...it/58ss-1p.pdf

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Originally Posted by hvac1000

One of the original Carriers and it is still running. Does it have the three wire pilot. If so that can give you a fit sometimes. They will allow the unit to run then drop out of the circuit at any time. the link is for some of the original specs on that unit.


http://www.xpedio.carrier.com/idc/gr...it/58ss-1p.pdf

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Yes it has the 3-wire. I replaced it last season. At that time I bought the main control board because a tech that came out said that was the problem. It ran for awhile with just the ignitor assy replaced and so I did put the board in and it seemed OK all last year and some of this year. Then it started some similar behavior this year. Looks like the relay contacts in the inducer board were messed up because cleaning them has seemed to make the problem go away, at least in the last 3 starts today.

Yes I read where you had replaced the three wire pilot. Just because it is almost new does not mean it is working correctly was the point I was trying to make. Over the years I have had them fail with in a week of replacement so I was just mentioning the fact of not taking that off the list of possibilitys. They are adjustable but that is something best left to the pro's since it is a safety device.

Back in the day we sold many of those SS models of Carrier. For the time they were a good unit except if you got some of the originals with the cold rolled steel heat exchanger. They rusted out quick but they were replaced with aluminized steel and those lasted longer.

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Originally Posted by hvac1000

Yes I read where you had replaced the three wire pilot. Just because it is almost new does not mean it is working correctly was the point I was trying to make. Over the years I have had them fail with in a week of replacement so I was just mentioning the fact of not taking that off the list of possibilitys. They are adjustable but that is something best left to the pro's since it is a safety device.

Back in the day we sold many of those SS models of Carrier. For the time they were a good unit except if you got some of the originals with the cold rolled steel heat exchanger. They rusted out quick but they were replaced with aluminized steel and those lasted longer.

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Yes I heard that about this unit from the Lennox dealer here. He originally installed a lot of carriers and remarked that my HX looked good. Yes I suspected the ignitor too. I noticed that the gap can be set but I didn't see any other adjustment on it. It has a fixed orifice. That seems to be working and lighting off correctly so let's hope that's not it. There are about 100 of these carriers in my development. I wonder if any have had this many problems. It was trouble free for about 20 yrs so I can't really complain.

Do not expect to get 20 years of trouble free service out of any of the new ones since that will never happen. I guarantee you will be spending some big $$$ if you buy a variable speed blower on any unit after the warranty is over. While the DC conversion has merit the true long range cost/energy savings are bogus.