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  1. #1
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    Question Flame Sensor Fluctuations

    I'm two months into the industry - working PMs...ran across a Lennox SLP98UH135XV60D-09, fired it up and watched it fluctuate between 2.1 a 6.6uA...think it listed nominal from 4-6..system ran within specs...flame looked good. Is it normal for some to fluctuate?

    What am I missing? Appreciate any advice...

  2. #2
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    Checking from the control board? You won't get an accurate reading with a meter on that furnace.

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  4. #3
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    All systems will fluctuate somewhat by simple virtue of the flame being fluid. The spread you list is pretty dramatic, however I also question whether you are just using test points on the board, which most furnaces do not have. Make sure you know how to test it with your meter in series with the flame rod and board.

    That said, I only test when there is an issue. Even when I know it's a flame recognition issue based on the way it flames out (fairly quickly after ignition), I like to see the before and after results. Also on mystery intermittent issue calls. On a simple PM I just clean the rod out of habit, much faster.
    Is the Religious Right to blame for Christianity's decline?

    They argued that, as the Religious Right became increasingly visible and militant, it became associated with Christianity itself. And if being a Christian meant being associated with the likes of Jerry Falwell, many people—especially political moderates and liberals—decided to simply stop identifying as Christians altogether.

    http://www.theamericanconservative.c...nitys-decline/

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  6. #4
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    Quote Originally Posted by hurtinhvac View Post
    On a simple PM I just clean the rod out of habit, much faster.
    Same. In school I was taught how to use a meter to check but the guy I was learning from on the job told me to just clean the flame sensor and call it a day because if it's actually bad you'd know it.

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  8. #5
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    Thread Starter
    Normally test in series - sometimes get lucky with the board current pad...
    - I tested in series with my meter, Flame Rod - Meter - Flame Rod connector.
    - I did pull the sealed combustion plate off to do the check...it was a super tight setup so I left if off during the check.
    - This was my third call of the day - all the others before and after registered solid and in range +/- .1 while running.

    I've had this happen a few times previously - all except one were in working order, nothing unusual - no prior issues and each call was a PM. I always test after it's pulled and cleaned. Being a numbers guy, the fluctuations drive me nuts...just want to make sure I'm not missing something.

  9. #6
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    If you're worried about it swap it out they are a cheap part that's the P in PM.

  10. #7
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    Knock yourself out, but you'll likely end up not wasting the time at some point in the near future. Anything over two is good. I've watched them drop down to .4 on malfunctioning systems before flame out and after cleaning bounce up to over 2 and be good for another so many years. Don't be looking for +/- .1, I haven't looked at what any system requires in years - if they mention it at all.

    By the way, the only time you would ever replace a flame rod is if the ceramic insulator breaks, which I have never seen happen yet. And don't get caught up in all the nonsense about how to clean them properly...you could use your shirt sleeve and be perfectly adequate.
    Is the Religious Right to blame for Christianity's decline?

    They argued that, as the Religious Right became increasingly visible and militant, it became associated with Christianity itself. And if being a Christian meant being associated with the likes of Jerry Falwell, many people—especially political moderates and liberals—decided to simply stop identifying as Christians altogether.

    http://www.theamericanconservative.c...nitys-decline/

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  12. #8
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    Fair enough - will throw an extra shirt in the van tonight! Appreciate the feedback all

  13. #9
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    Check your ground as well. Most flame rectification issues are actually grounding issues. Test neutral to ground. Voltage should be below 2 vac

    Sent from my SM-G935T using Tapatalk

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  15. #10
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    Quote Originally Posted by Wrightflyer2 View Post
    Fair enough - will throw an extra shirt in the van tonight! Appreciate the feedback all
    Extra shirt? Don't go being a hero just use whatever you are wearing.

  16. #11
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    - I did pull the sealed combustion plate off to do the check...it was a super tight setup so I left if off during the check.

    That door off could have disrupted the way that flame acted as compared to when the door is on. Have fun in the biz guy. I still love it for the most part after 40 plus years.

  17. #12
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    The slp98 is a modulating furnace from 35% to 100% I'm sure that when it starts in low stage the flame sensor will read a little different than high stage maybe that's the fluctuations your seeing

  18. #13
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    A lot of newer units modulate the voltage to the flame sensor up and down. I have seen many newer rheem units doing the same thing. I saw this on a newer goodman and called tech support about it. I was told that technically I needed an oscilloscope to properly read it and as long as it was over .50ua good to go


    Sent from my SM-N920V using Tapatalk
    ...

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