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Discussion Starter · #1 · (Edited)
Nordyne M1M Series Propane Burner w/Intergrated Furnace Control Board, furnace 7-years old. Nothing known about its history.

Upon arrival, initially check out furnace visually, and while doing so owner starts adjusting mechanical tstat, producing a violent stuttering of the gas valve, but only momentarily... maybe a long 1-second or so. Not long after, I find the protective cardboard insert still in place in the tstat. I could take a stab at it, but not sure of its exact purpose. The protective part of the insert surrounds the vertically positioned center-post that moves between the two contact points on either side of the center-post as you adjust room temp setting.

After a new board installed, all is well again. Only much later after upgrading the tstat to digital (also figuring the stuttering was due to the cardboard insert still being in place), do I find out that this occasional stuttering had been going on during furnace operation for at least a couple months, but not sure exactly how often. Daughter was the only one home most of the time and was the one who told me that the furnace "was doing that a lot."

Could the "stuttering" have been what killed the board? Yes, or Poo-poo?
 

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What (if anything) was the system doing when you got there? Just trying to better understand the background of replacing the board.

PCB relays are typically rated at about 250K total average life cycles. Certainly rapidly cycling them could cause harm. Doesn't actually take too many make/break cycles with arcing to damage or weld the contacts. The micro and most other components would not really tend to care to my knowledge. Any chance you suspect a bad relay on the original board?
 

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Would have to see this cardboard so next time take a good pic of it. Only cardboard I ever saw was to hold the mercury bulb still so it did not bounce around during transport and mess with the bi-metal spring.

I doubt it caused the stuttering. Once again I wil explain the sequence of operation Young Grasshoppa and you may want to memorise it.:vs_bulb:

Tstat calls for heat and energises board and a prepurge occurs and closes press switch and then energises HSI and fires burner and proves it. IF the flame is not established or drops out quickly then ALL furnaces restart the prepurge cycle to remove excess gas and eliminate explosion risk. So if your dude caused the tstat to stutter what should happen?

Board should recycle and restart prepurge cycle not mess with the valve.:wink2:

I suspect the board relay was chattering for the gas valve due to a weak relay. They go that way. Mine started chattering/dropping out the inducer after 10 yrs.

It is VERY important to understand the sequence of operation. If you have Nordyne or Miller manuals or access to them and they have a troubleshooting flow chart get it and print it and study it. Will make your life a LOT easier and once you know it they all work the same way.

Here is a site with a manual for a Lennox G51 which is a basic furnace that has a flow chart for troubleshooting and every single stage furnace works the same way. Start at page 41.

http://www.hvacpartsshop.com/manuals/G51MP_Series.pdf


http://www.hvacpartsshop.com/manuals/lennox-furnace-service-manuals.html
 

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Mechanical dry contact thermostats come with a protector to prevent(that should be removed after installation) the moving contact from being damaged by harsh handling during shipping, and installation.

It may have harmed the board after years of working like that. And probably not always making good contact.
 
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Discussion Starter · #5 · (Edited)
What (if anything) was the system doing when you got there? Just trying to better understand the background of replacing the board.

PCB relays are typically rated at about 250K total average life cycles. Certainly rapidly cycling them could cause harm. Doesn't actually take too many make/break cycles with arcing to damage or weld the contacts. The micro and most other components would not really tend to care to my knowledge. Any chance you suspect a bad relay on the original board?
Yepper, that's exactly what I suspected (bad relay), and your statement above in red is also exactly what I had in mind when asking my question. That's really all I wanted to know (if the violent, rapid-fire stutter was a possible reason for the board's (relay) failure), and I should have explained that was all I was after. Thx much for jumping in...

Would have to see this cardboard so next time take a good pic of it. Only cardboard I ever saw was to hold the mercury bulb still so it did not bounce around during transport and mess with the bi-metal spring.

I doubt it caused the stuttering. Once again I wil explain the sequence of operation Young Grasshoppa and you may want to memorise it.:vs_bulb:

Tstat calls for heat and energises board and a prepurge occurs and closes press switch and then energises HSI and fires burner and proves it. IF the flame is not established or drops out quickly then ALL furnaces restart the prepurge cycle to remove excess gas and eliminate explosion risk. Way ahead of you Master:yes: So if your dude caused the tstat to stutter what should happen?

Board should recycle and restart prepurge cycle not mess with the valve.:wink2: The stuttering was violent (rapid & a bit loud) because it was the valve that was stuttering. Don't know that it didn't drop out at some point and restart prepurge -- owner starts adjusting tstat as I'm walking up to the furnace... valve starts stuttering, shocks me a little, and immediately takes my attention away from furnace, and redirects to the owner and tstat! "What the :censored: are you doin' over there... I'm workin' here!":vs_mad: :laughing:

I suspect the board relay was chattering for the gas valve due to a weak relay. They go that way. Mine started chattering/dropping out the inducer after 10 yrs. Yepper, recently had a Goodman HE unit. Inducer made a few weak attempts to run, then wouldn't run at all. Started tapping on the board relays and inducer turned a few times when I found the right one, then stopped. Tapped some more and inducer motor half-shell would jump in unison with my tapping. New board and all was well again.

It is VERY important to understand the sequence of operation. If you have Nordyne or Miller manuals or access to them and they have a troubleshooting flow chart get it and print it and study it. Will make your life a LOT easier and once you know it they all work the same way. Waaaayy ahead of you regarding sequence of operation (long time ago I mean), but how could you be expected to keep up, because I have only one "Master":notworthy:, but you have many "students." :yes:

Here is a site with a manual for a Lennox G51 which is a basic furnace that has a flow chart for troubleshooting and every single stage furnace works the same way. Start at page 41. My sincere gratitude Master, but already have same thing (or something very similar by Goodman. Also noticed that your hvacpartshop.com site has the Goodman Service Manuals also.

http://www.hvacpartsshop.com/manuals/G51MP_Series.pdf


http://www.hvacpartsshop.com/manuals/lennox-furnace-service-manuals.html
The exact same tstat (not the "actual", but online pic of), but I still had the cardboard insert in my tool bag. This mechanical tstat was changed to digital.

"Grasshoppa"...
 

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Discussion Starter · #6 · (Edited)
Also maybe (maybe not?) be worth mentioning that at one point when I started to pull the cover off the tstat, it also gave an initial "one beat of a stutter", so I gave up immediately at that moment for the time being. I was pulling on the cover the correct way.

It never would come off easy like others have (same model stat). Was having to hold the base steady (at least attempt to) while pulling on the cover... still had much trouble with that. The base wasn't loose however.
 

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LOL, I've had more then one stat kick my butt trying to get the cover or it off of the base.
 

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Are you makin' fun of me again (and so early in the morning!). Well then... :boxing: :laughing:

Oops, it's already 7:30 AM (I know how early you're up sometimes)

Its real embarrassing when the customer says, you know it has a release button on the bottom. :vs_mad:
 
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Discussion Starter · #11 · (Edited)
The red arrows in the pic below show what appears to be adjustable contact points (never noticed/ looked at 'em closely before, in person). This for adjustability by the factory only, or for accuracy adjustment in the field maybe?
 

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Calibration screws. can be recalibrated in the field. But it cost more to do so, then to replace. If you are taking the time to do the calibration correctly.
 
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