Author Topic: Multiple problems...  (Read 3381 times)

Offline DavidIMcIntosh

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Multiple problems...
« on: November 06, 2018, 12:07:51 AM »
I am having a few problems with my furnace.
Is a Lennox 80MGF3-75a-2.  The control board on it is an EGC1 (1173-1).

When trying to ignite, it fails intermittently with the Watchguard code ("failed to ignite").
When I watch it trying to ignite, I can see and hear that it goes through all the proper steps: combustion air blower starts, then after not too long - 20 seconds maybe - I can hear the gas valve open and the gas start to flow.  At the same time, I can hear the igniter trying to spark, and I can see a very very brief spark on the igniter tips.  but the spark lasts only a fraction of a second, NOT the the full 1 to 4 seconds that the docs say it should last.  After 4 to 5 seconds of the gas running and not igniting (no spark really), I hear the gas turn off.  20 to 30 seconds later, it tries again.  It tries a few times  - maybe 3 to 5, I can't recall, but the correct number of tries, as per the manual - before going stopping the combustion blower and going into watchguard mode.  _Sometimes_, the very brief spark will be enough to ignite, but that is happening less and less often.

I have removed the igniter and cleaned it with 400grit emery paper.  I measured the gap and it is exactly to specification in the manual.  I have measured the resistance on the spark cable (10 or 20K ohms, can't recall exactly, but it seemed reasonable for a high-voltage spark cable).

So, I am thinking it must be a problem with the board, not the igniter itself.  Is this reasonable?

Second problem: when it does light, it needs to run for a longer-than-usual time span (due to not being able to run always), and this results in one of the two flame roll-out switches cutting out (it's always the same one).  I noticed the vent pipe for the furnace has screen over it at the outside, and the screening is pretty clogged.  I have just now removed the screen and will see if the flame roll-out switch stops cutting out, but is this a reasonable possible cause for the flame roll-out cutoff going?

Thanks for any comments.

Offline Admin

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Re: Multiple problems...
« Reply #1 on: November 06, 2018, 06:21:19 AM »
That does sound like a board problem if you witnessed shorter spark times.  I have seen overfired gas valves that prevent the burners from firing because the gas pressure is too high.

Isn’t that furnace vented up through the roof?  It should have a chimney cap.  I would think the pressure switch would trip before the roll out if the vent was blocked.  You may have a cracked heat exchanger and should have it inspected.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #2 on: November 06, 2018, 10:41:21 AM »
That does sound like a board problem if you witnessed shorter spark times.  I have seen overfired gas valves that prevent the burners from firing because the gas pressure is too high.

Isn’t that furnace vented up through the roof?  It should have a chimney cap.  I would think the pressure switch would trip before the roll out if the vent was blocked.  You may have a cracked heat exchanger and should have it inspected.
Thanks for the reply.
Furnace worked fine for years and I don't think the gas pressure has changed.
Furnace is not vented through roof - it's vented out the side of the house.  Vent was not totally blocked, just significantly.  Flame roll-out has not tripped since I removed screening, but on the other hand the ignition problem is still there and not clear it has fired much since I removed screening.
I have ordered new board.  In the market for controller boards, I am guessing the huge price differences I am seeing are the difference between China knock-offs and OEM boards?  If the cheaper boards are knock-offs, are they reliable?  Or is the price differential possibly due to sellers wanting to get rid of old stock for furnaces that are disappearing and dying fast?

After I install the new board, I will do the match test (with gas off of course) as per other threads, for heat exchanger crack.

Offline Admin

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Re: Multiple problems...
« Reply #3 on: November 06, 2018, 11:40:12 AM »
They must have used a sidewall power vent kit because that's a mid efficiency furnace.

I have seen bad gas valves that cause a higher manifold pressure, so high that the gas won't ignite when it passes over the spark.  This has nothing to do with the gas supply pressure, but it does sound like a bad board in your case.

A blocked vent could certainly cause the roll out switch to trip.

Be careful which board you order, that furnace has had a lot of revisions.  It depends on the serial number and model dash number.  If you post your serial number I can tell you what part number you should order.

Quote
Note1:
DASH 3 THRU DASH 11 BEFORE SERIAL NUMBER 6399E14048 MANUFACTURED WITH
27K15.

Note3:
USE 20J85 FOR RAM IGNITION BOARD (BARBED FITTING CONNECTION). USE
LB-91096A (76K20) FOR HEATCRAFT IGNITION BOARD (1/4 QUICK CONNECT).

Note5:
ORIGINAL PART 33J62 (RAM). IF KIT LB-84495A (EGC CONTROL-HEATCRAFT) HAS
BEEN INSTALLED, ORDER LB-91097B (HEATCRAFT) AS REPLACEMENT.

Note6:
ORIGINAL PART 20J80 (RAM). IF KIT LB-84495A (EGC CONTROL-HEATCRAFT) HAS
BEEN INSTALLED, ORDER LB-91097B (HEATCRAFT) AS REPLACEMENT.

Offline NoDIY

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Re: Multiple problems...
« Reply #4 on: November 06, 2018, 07:15:40 PM »


On some of those mids lennox had an ignition upgrade kit that came with updated wires sensors and ignitors.. maybe time for an upgrade. Also on older models the ventor housing was painted black inside and out and would flake paint and cause pressure switch issues(im thinking yours though is a non painted silver housing..)

The sidewall powervent is concerning. Those things are pushing 20 years now. can start to have issues. The inducer wheel can get caked with years of crap..

Id have a tech in to look the system over in detail.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #5 on: November 07, 2018, 08:11:24 PM »
NoDIY:

Silver housing, not painted black.  No pressure switch issues - motor is fine, bushings are still fine.  I may service the inducer wheel based on your comment, should be easy to clean.

I have two acquaintances who are HVAC Techs.  One is now doing a PhD at Harvard in nano-technology - brilliant guy.  The other is stupid as a stump, couldn't figure out the simplest issue to save his life.   Point is, getting an HVAC Tech (like absolutely any profession) to inspect is a crap shoot - brilliant guy like the first would do a way better job than I; dumb guy like the second might easily blow the place up.  I've fixed _everything_ in my life for over 45 years, there's not much I haven't dismantled and fixed at some point. I'll take reliance on my self-sufficiency... ;-)

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #6 on: November 07, 2018, 09:24:56 PM »
I see there are fiber-glass gaskets between housings that would need to be dismantled to service inducer wheel.  I haven't replacements, so I will leave well-enough alone.  Flame roll-out switch went again however, so I am beginning to wonder if the roll-out switch needs to be replaced as well.  I may post video of burner in operation for comments.

One question: given position of roll-out switch, how could a leak in the heat exchanger cause roll-out switch to trip?

Thanks for all comments, btw.  Much appreciated.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #7 on: November 07, 2018, 09:39:37 PM »
They must have used a sidewall power vent kit because that's a mid efficiency furnace.
Implication of "mid-efficiency" being that vent gasses are still fairly hot hence side venting is not straight-forward.  The side vent is tin, not ABS/PVC, and co-joined with the vent from the hot water tank.  What is a power-vent-kit?
... Be careful which board you order, that furnace has had a lot of revisions.  It depends on the serial number and model dash number.  If you post your serial number I can tell you what part number you should order.
...
I can find nothing on my board that look like the standard model numbers (i.e. xxLxx where x is a digit and L is a letter).
Serial number of my furnace is 6394D86964.  Model is 80MGF2-75A-2.  Board is EGC1.  Number that looks most like a model number on the board is 1173-83-1A, but I have not seen any board model numbers with "1173", so I have no idea what the model is.  But board looks absolutely identical to the 19W94 that I ordered (https://www.ebay.com/itm/232962807343).  Description of board in online ad says it is used on the Lennox model 80MGF2-75A-2 (among many others...)

Offline Admin

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Re: Multiple problems...
« Reply #8 on: November 08, 2018, 07:26:31 AM »
It looks like part #19W94 is the latest control board for the -2 model.

Quote
Part 19W94 replaced 33J62 replaced 65K07 replaced LB-84495A replaced LB-84495B replaced 33J6201

I have never seen a mid efficiency furnace vented out a side wall.  The kit is no longer available but was part #79J15.  I assume there would be a second exhaust motor installed on the vent itself.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #9 on: November 08, 2018, 01:00:25 PM »
It looks like part #19W94 is the latest control board for the -2 model.
Thanks for this! I really appreciate this!  Good to know I didn't just throw $300 away.
I have never seen a mid efficiency furnace vented out a wall.  The kit is no longer available but was part #79J15.  I assume there would be a second exhaust motor installed on the vent itself.
Yah ... no, there isn't.  Sigh.  At least the vent pipe has a good upward slope in it, about 30%.  And as I said, it's co-joined with the vent on the (gas) hot water tank.  Gotta love Enbridge.  It may then be the reason the one roll-out switch keeps tripping, that or i need a new roll-out switch too...

Offline Admin

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Re: Multiple problems...
« Reply #10 on: November 08, 2018, 03:34:19 PM »
What kind of water heater do you have?  It's vented out the side wall too?  I have never seen a conventional vent water heater (metal venting) vented out a side wall.  I'm really not sure how that would have passed inspection.

At some point you should be looking to upgrade the furnace to a high efficiency model and then look at buying or renting a power vented water heater.  Both would use the plastic venting and are approved for side wall venting. 

It sounds like there are some serious installation issues there.  Be safe!
 

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #11 on: November 08, 2018, 08:28:43 PM »
Actually, I was wrong and you guys were completely correct.  There are two vent pipes that cross and I hand not followed them carefully, or correctly!  The furnace and water exhausts _are_ co-joined, but they do indeed vent out the roof.  So no safety issue there.

Which leaves me back to diagnosing why the one roll-out switch is tripping.  I will wait until I have the new board installed (and thus hopefully solve the ignition problem) before trying to diagnose the roll-out cut-off problem.

Offline NoDIY

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Re: Multiple problems...
« Reply #12 on: November 08, 2018, 09:05:03 PM »
Roll out switch tripping can be from a cracked heat exchange or blocked chimney liner(rotting). A blocked or partially blocked liner can give intermittent issues with the way the furnace vents.

Maybe post a picture where they enter the vertical part of the chimney. Water heater and furnace common venting into a chimney is normal.

Post a picture of the top of the water heater, see if there are signs of spillage

Offline Admin

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Re: Multiple problems...
« Reply #13 on: November 09, 2018, 07:22:07 AM »
Don't forget to put the screen back.  It's was likely on the outdoor air supply duct.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #14 on: November 09, 2018, 08:22:06 AM »
Don't forget to put the screen back.  It's was likely on the outdoor air supply duct.
I was going to put back a coarser screen, the type that one typically uses on chimneys, with a larger grate size: small enough to keep small animals out but large enough not to get clogged with dust.  Perhaps that is not a good idea? I would allow earwigs and other insects in, but something small enough to keep ear-wigs and insects out will get clogged.  Advice?

Offline Admin

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Re: Multiple problems...
« Reply #15 on: November 09, 2018, 08:26:31 AM »
The Building Code says the openings shall be a minimum 15mm (1/2”).  That’s not small enough to keep out insects.  You could use smaller as long as it doesn’t interfere with the air supply.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #16 on: November 09, 2018, 09:24:29 AM »
Roll out switch tripping can be from a cracked heat exchange
Many people have said that.  That does confuse me though: how can a cracked heat exchange cause flame roll-out at the intake (where the flame roll-out cutoff switch is)?
or blocked chimney liner(rotting). A blocked or partially blocked liner can give intermittent issues with the way the furnace vents.
This makes sense.
Maybe post a picture where they enter the vertical part of the chimney. Water heater and furnace common venting into a chimney is normal.
Post a picture of the top of the water heater, see if there are signs of spillage
Would it be at all informative to see a picture of the flames while the furnace is running?  I don't know how much flame outside of the heat-exchanger tubes is normal.  There is some amount of flames from small amounts of gas seeping through joints in the venturi.  I presume that is normal, but these smaller flames are not completely sucked into the heat exchanger tubes, and they are certainly heating up the housing on which the flame roll-out switch sits.

Offline Admin

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Re: Multiple problems...
« Reply #17 on: November 09, 2018, 10:29:39 AM »
Once the heat exchanger heats up, any cracks may open up wider.  When the main blower starts it can cause air to blow into the crack and then cause the burner flames to start to roll-out the front of the burner box.

Offline viking

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Re: Multiple problems...
« Reply #18 on: November 09, 2018, 04:56:53 PM »
There should be no flame outside if the heat exchanger and certainly no flame coming out of the venturi.
Sounds to me like you have a combustion side problem. Cracked heat exchanger, dirty burners, high manifold pressure or something.
Be very careful. The flame roll out tripping is trying to tell you something.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #19 on: November 10, 2018, 01:04:59 AM »
Once the heat exchanger heats up, any cracks may open up wider.  When the main blower starts it can cause air to blow into the crack and then cause the burner flames to start to roll-out the front of the burner box.
Ahhh, that makes sense now.
This is not happening that I can see: there really is no roll-out happening that I have seen.  The roll-out switch only cuts off when the furnace runs a very long time, like 25 minutes.  This is why I think it may be just a switch with a slightly low trip temperature.  And maybe my main blower is not operating that well, so not enough heat is being extracted from the exchanger and after enough time, the housing heats up too much.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #20 on: November 10, 2018, 11:07:35 AM »
There should be no flame outside if the heat exchanger and certainly no flame coming out of the venturi.
Sounds to me like you have a combustion side problem. Cracked heat exchanger, dirty burners, high manifold pressure or something.
Be very careful. The flame roll out tripping is trying to tell you something.
I must be using the wrong terminology: what I was calling the venturi are the short trumpet-shaped metal tubes where the gas shoots down and is mixed with the air being sucked through them.  Where the gas and air mixture _exits_ these tubes is where the combustion starts, and the flames extend from the exit of these tubes into the heat exchanger tubes.  It looks pretty OK to me.

Offline Hgye

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Re: Multiple problems...
« Reply #21 on: November 10, 2018, 02:11:27 PM »
Quote
I must be using the wrong terminology: what I was calling the venturi are the short trumpet-shaped metal tubes where the gas shoots down and is mixed with the air being sucked through them.  Where the gas and air mixture _exits_ these tubes is where the combustion starts, and the flames extend from the exit of these tubes into the heat exchanger tubes.  It looks pretty OK to me.


A tripped roll-out is a serious safety concern on a furnace, and there is a chance you have a cracked heat exchanger.    You may be handy, but you obviously don't have the skills or tools necessary to rule out a cracked heat exchanger.  You have been advised multiple times that your heat exchanger may be cracked.  This problem is not as complex as you are making it out to be.  Have your furnace checked out by a professional.  Your life may depend on it.

Offline NoDIY

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Re: Multiple problems...
« Reply #22 on: November 11, 2018, 04:13:56 PM »
Quote
I must be using the wrong terminology: what I was calling the venturi are the short trumpet-shaped metal tubes where the gas shoots down and is mixed with the air being sucked through them.  Where the gas and air mixture _exits_ these tubes is where the combustion starts, and the flames extend from the exit of these tubes into the heat exchanger tubes.  It looks pretty OK to me.


A tripped roll-out is a serious safety concern on a furnace, and there is a chance you have a cracked heat exchanger.    You may be handy, but you obviously don't have the skills or tools necessary to rule out a cracked heat exchanger.  You have been advised multiple times that your heat exchanger may be cracked.  This problem is not as complex as you are making it out to be.  Have your furnace checked out by a professional.  Your life may depend on it.

THIS ^

Offline Hvacpimp

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Re: Multiple problems...
« Reply #23 on: November 19, 2018, 07:38:27 PM »
NoDIY:

Silver housing, not painted black.  No pressure switch issues - motor is fine, bushings are still fine.  I may service the inducer wheel based on your comment, should be easy to clean.

I have two acquaintances who are HVAC Techs.  One is now doing a PhD at Harvard in nano-technology - brilliant guy.  The other is stupid as a stump, couldn't figure out the simplest issue to save his life.   Point is, getting an HVAC Tech (like absolutely any profession) to inspect is a crap shoot - brilliant guy like the first would do a way better job than I; dumb guy like the second might easily blow the place up.  I've fixed _everything_ in my life for over 45 years, there's not much I haven't dismantled and fixed at some point. I'll take reliance on my self-sufficiency... ;-)

Not to put you down or anything but just because they are great in schools doesn't mean that they are great with the hands on trade work and vise versa! Honestly, if it took you a few tries to figure out the venting, it maybe time to call a professional. You probably are right with regards to the control board being faulty but if we have to explain about cracked heat exchangers and symptoms, especially with a furnace of that age, you may need a second opinion. Be also careful of a potential delayed ignition. The only reason I say this is in my 18 years in the trade I witnessed first hand of a guy trying to fix venting himself and almost killed his family. I was questioned because I was the one who wrote the initial tag

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #24 on: November 23, 2018, 05:36:38 PM »
  I don't know how much flame outside of the heat-exchanger tubes is normal.  There is some amount of flames from small amounts of gas seeping through joints in the venturi.  I presume that is normal, but these smaller flames are not completely sucked into the heat exchanger tubes, and they are certainly heating up the housing on which the flame roll-out switch sits.
Well, I have figured out the purpose of the flames from the small amounts of gas seeping out between the sheet-metal wings at the flame-end of the burners.  The burners are clearly designed to have a small amount of gas seeping out there, and small flames there. It is these small flames that carry the flame from one burner to the next during the ignition stage.  If the burners were designed to only allow gas through the main venturi and into the heat exchanger, only the right most burner where the igniter is would light.  This is also why the flame sensor is on the left most burner - the flame must traverse completely from right to left at ignition to get the left most burner (and hence necessarily all the other burners) going for the flame sensor to activate, otherwise things shut down for obvious safety reasons.  All quite clever.

Offline viking

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Re: Multiple problems...
« Reply #25 on: November 24, 2018, 05:19:50 PM »
Yes. It’s called carry over. And also correct. Ignite at one end and sense on the opposite end.
Did you get the board and flame roll out fixed?

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #26 on: November 26, 2018, 12:19:30 PM »
Board has not arrived yet - between our postal strike, border problems, and possibly supplier issues, I have no idea where it is at present.  And this, the coldest fall I can recall.  What fun.

Yes, the flame-roll-out triggering is fixed.  If I get the time, I will post a photo of the sheet-metal side-wall beside the right most burner.  It is corroded where the (unnecessary) right-most carry-over flame was far too large.  I guess the right most burner was just poorly manufactured.  The left side was fine, but you can clearly see where the right side flame was hitting the side wall and corroding it.  That's why it was always the same side - the right side - that was triggering.  That's also why I asked a way back about the expected size of these "carry-over" flames, which at the time I did not clearly see the reason for.  The left most and right most "carry-over" flames are unnecessary, just an artifact of manufacturing all the burners identically.  I clamped down the carefully blocked the right most carry-over flame with some very small clamped sheet metal on the burner.  Now the roll-out switch never triggers.

I had taken a time-lapse video of the burners from ignition to when the roll-out switch triggered.  The flames never changed - no evidence of any heat exchanger crack or anything.  It was just a slow process of the housing heating up because of the excessively large right-hand carry-over flame.  I never had problems when the ignition was working: the furnace never had to run long enough to trigger the roll-out switch.  With the ignition not working properly, the furnace is only being turned on twice a day, and has to run a long time to heat the house.   Running that long caused the housing to heat up from the excessive carry-over flame.  The excessive carry-over flame has always been there though, you can see by the corrosion on the side-wall.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #27 on: November 26, 2018, 02:43:13 PM »
Side wall corrosion

Offline Admin

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Re: Multiple problems...
« Reply #28 on: November 26, 2018, 04:01:41 PM »
How did you prevent that from tripping the roll out switch?

I believe that's the first burner to see gas.  I wonder if the manifold pressure is too high.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #29 on: November 26, 2018, 05:08:01 PM »
How did you prevent that from tripping the roll out switch?

I believe that's the first burner to see gas.  I wonder if the manifold pressure is too high.
That's the burner with the ignitor, so its the first burner to see flame, yes.
You see the corrosion on the wall beside it (open the image by itself in another tab and magnify it)? That's because the very right most burner itself had too large an opening on the very right for the carry-over flame, and this (unnecessary) carry-over flame was large and hitting the side wall there and heating it.  Since there is no need for _any_ carry-over flame on this very right most side (you only need the carry-over between the burners), I simply blocked the carry-over crack on the right most flange of the right-most burner.  Then there is no flame on the side wall, and the flame-roll-out stopped triggering.  Poorly manufactured burner, combined with my furnace having to run for an hour or more each time I start it because of the ignition problem.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #30 on: November 28, 2018, 10:23:26 PM »
Oh man.  New board was finally "delivered" today by Canada Post - one month after ordering it.  Except instead of delivering a board, they delivered a "pickup" notice with a fee of $50, presumably customs duty.  How nice, $50 duty on a $250 board, 20%.  Highway robbery by customs.  Anyway, hopefully by tomorrow evening I will have a properly working furnace.

Roll-out switch hasn't triggered once since my fix, even when the furnace has had to run non-stop for 1.5 hrs after being off for the day, in this cold weather.

Offline NoDIY

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Re: Multiple problems...
« Reply #31 on: November 29, 2018, 09:09:25 PM »
Hopefully you have the heat exchanger checked, manifold pressure checked and combustion analysed at some point.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #32 on: November 30, 2018, 12:05:58 AM »
Hey Admin, when you said
I believe that's the first burner to see gas.  I wonder if the manifold pressure is too high.
I think I miss-understood you. Thinking about this again, did you mean that this burner (the one in the photo, on the right) is the one that is closest to the gas source, i.e. first along the path of the gas (because, yes, it is)?  In other words, were you suggesting that, because this is the first burner along the gas path, it might have a (slightly) higher manifold pressure that the other burners, and as a result, might have more gas being forces out the carry-over slots?  Is that what you were getting at?  Interesting idea.

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #33 on: December 01, 2018, 01:31:02 PM »
Right, so, I picked up my new board.  Now, before ordering the board, I measured the resistance of the ignitor cable.  It's 10K ohms, with no evidence of variation due to a break, i.e. I cannot wiggle it anywhere to make the resistance fluctuate.  So it _seemed_ fine.  At which point, I'm left with a decision: is it the board (a few hundred bucks, and comes with a new cable), or just the cable (almost a hundred bucks just for the bloody cable).

Given I'd measured the cable and it seemed fine, I opted for a new board.

It came with a new cable.  On the off chance it was just the cable, I tried just replacing the cable before replacing the whole board.

Sigh.  First ignition attempt successful.  Maybe it was just the cable after all?  I shall wait for a few more ignition attempts and see.

Can anyone tell me what the resistance of one of these cables should be?  I couldn't find it anywhere, and from what I know about high tension cables, 10K ohms seemed reasonable.  Online info was about 10k ohms per metre, and the length is about 50", so that should be about 12.7K ohms.  And if I was correct about what the resistance should be, but I was wrong that the cable is OK, how could/should I test the cable to see that it was bad (besides replacing with a known good cable, that I didn't have...)?

Offline DavidIMcIntosh

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Re: Multiple problems...
« Reply #34 on: December 01, 2018, 01:56:12 PM »
Yep.  Tested multiple ignition attempts.  10 tests, 10 successful ignitions, 0 failures.  Anybody want a brand new board?  lol.

Offline Porcupinepuffer

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Re: Multiple problems...
« Reply #35 on: December 09, 2018, 09:47:59 AM »
Measuring the resistance of a high voltage ignition cable isn't much of any use. It works if there's an obvious break in the wire and you had infinity; then you know it's the wire and it needs replacing. In the case of a cable where the measured resistance is good and within spec, the wire can still be faulty once the high voltage sparks are sent out to do their job by jumping prematurely through weak insulation to spots they shouldn't, or heat from the sparking changing the resistance values enough to be out of spec that you wouldn't spot it with a lower voltage meter by ohming it out.

Offline BenBear

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Re: Multiple problems...
« Reply #36 on: January 03, 2019, 07:34:12 AM »
Great thread.

Offline neisg1

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Re: Multiple problems...
« Reply #37 on: February 16, 2019, 10:13:47 AM »
Just to clarify
Part #19W94 is the complete conversion kit  includes wiring adapters, metal mounting panel, high voltage spark wire, and the EGC1 board.
Part #17W82 includes only the high voltage spark wire, and the EGC1 board.
Both are the same EGC1 control board.

The spark cable is a resistance type similar to automotive spark plug wire and would normally be around 10k ohm.

I had the same high voltage issue with the spark getting weaker over a few months. I ended up replacing the control board to solve the problem.

Offline neisg1

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Re: Multiple problems...
« Reply #38 on: February 16, 2019, 12:11:43 PM »
The high voltage utilizes a capacitive discharge ignition similar to that used on cars.  The 24vac is connected to a step up transformer (the one with the yellow tag) that provides approximately 120vac. This is rectified by a diode and provides 120*1.414 = 169 volts dc to charge a 2.2uf 200v capacitor. This capacitor is then discharged through an SCR into the primary of the ignition coil. The secondary of the coil then producing a several thousand volt spark output. I have not figured out the trigger circuitry for the SCR yet but it has to be pulsed somehow.  So far I have substituted a known good ignition coil and tested all the main components, everything test good so far but still no high voltage.  I am suspecting that the 2.2uf 200v cap may be leaky and not providing a full charge. I have no way to test for leakage so I ordered a new capacitor and will post back once verified. Wish there were schematics available for these boards.

Offline neisg1

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Re: Multiple problems...
« Reply #39 on: March 01, 2019, 10:28:40 AM »
Finally got a 2.2uf 630v replacement capacitor. The board is now fully functional. The old capacitor tested good but must have been failing under load. The higher voltage rating on the new one will not affect function but gives a much higher saftey margin.

Offline Porcupinepuffer

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Re: Multiple problems...
« Reply #40 on: March 01, 2019, 02:46:46 PM »
You stuck to your word and did a follow up!
 It's a little more technical with the circuitry then all of us tech's get, but it's really interesting. I'm assuming you've taken courses in electronics before.

Offline neisg1

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Re: Multiple problems...
« Reply #41 on: March 01, 2019, 03:16:32 PM »
You stuck to your word and did a follow up!
 It's a little more technical with the circuitry then all of us tech's get, but it's really interesting. I'm assuming you've taken courses in electronics before.

Yes, I do have training in Electronics Engineering Technology. However, the actual capacitor replacement would be well within the capability of most electronics hobbyists.
I reinstalled this board back in the furnace and it has preformed flawlessly so far.

Offline Sergroum

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Re: Multiple problems...
« Reply #42 on: March 04, 2019, 11:58:04 AM »
The problem is that the moment you change that capacitor, the board's certification is under question. Not every tech is going to bother with that.