Limit switch Lennox G26Q 4/5-125-1

Discussion in 'HVAC Heating & Cooling' started by rmgolob, Dec 1, 2020.

  1. rmgolob

    rmgolob Member

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    Dec 16, 2016
    Location:
    Indiana
    The short question is does my furnace have the switch in the lower picture (From the internet) or does it only have the switch from the top picture (Actual picture from my furnace.)

    My crack research shows the bottom may be for older models. That is - even older that mine from 1998 +/-.

    I'm trouble shooting the issue of the fan not come on in the "AUTO" position. It does come on in the "OM" position.

    We have been running the fan 24 / 7 whether the burner is lit or not.

    I have ordered a 25J2601 and will try that, but looking for any insight.

    Thank you in advance,
    Rob

    Limit switch 2.jpg Limit switch.jpg
     
  2. rmgolob

    rmgolob Member

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    Dec 16, 2016
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    Indiana
    Sorry - I cannot figure out how to edit the thread.

    Paragraph 3 should state:
    "I'm trouble shooting the issue that fan does not come on in the "AUTO" position. It does come on in the "ON" position."
     
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  4. fitter30

    fitter30 Well-Known Member

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    Retired service tech
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    Burner fires (bottom pic) watch dial. Dial turns slowly as the dial turns the middle tab as it passes the middle of the control ( there is a raised line in the plastic) that turns on the fan, tap set at 195* is the high limit, tab far left fan off
    If you have air conditioning and motor is direct drive it is a multi speed motor. Heat will run at a slower speed than fan in the on position or air conditioning. Top pic where is that control mounted ( klixon) . Take a pic of the wiring diagram.
     
  5. WorthFlorida

    WorthFlorida The wife is still training me.

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    A good chance that it is a bad limit switch as you have ordered. If you have a volt meter there should be line voltage (120v) on the black wire and zero voltage on the red wire when not calling for heat. If you raise the thermostat to call for heat and after the phelmun reaches the set temperature voltage should be on the red wire. If there is and the fan motor is not running then it could be another problem. If the fan motor is 220v, which some are this may only be opening one side so you need to be careful. It's also why fitter30 asked for a picture of the wiring diagram.
     
  6. plumber69

    plumber69 In the Trades

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    You could also fire it up, let it run for a minute then start tapping on the limit. May just be stuck. Either way probably need new one
     
  7. WorthFlorida

    WorthFlorida The wife is still training me.

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    Just below your comments on the left is a timestamp with your username. Next to it is is a link for "Edit" and "Report"
     
  8. rmgolob

    rmgolob Member

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    Dec 16, 2016
    Location:
    Indiana
    Thanks Fitter.
    I believe you are implying that I DO have the switch in the bottom picture?
    If so, where is it? I don't see it in the pic below. (My Picture in the OP is from the internet) Is it inside of something?
    Yes, I DO have AC hooked to this unit. If I'm not mistaken, The AUTO setting works fine in the AC mode.
    To clarify my original post - When in heat mode and AUTO selected, the burner fires for about a minute. The fan never comes on. Then the unit shuts down (Correctly given the fan is not on.)
    All works fine in Fan ON mode.
    Thanks again.
    Wiring 26G Q4-5.jpg
     
  9. rmgolob

    rmgolob Member

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    Dec 16, 2016
    Location:
    Indiana
    Thanks Worth.
    Based on your "be careful" I will install the new switch and see what happens. I have and can use a volt meter but lack experience and knowledge with zero voltage, red wire, black wire, call for heat, etc...o_O
     
  10. rmgolob

    rmgolob Member

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    Dec 16, 2016
    Location:
    Indiana
    Thanks Plumber,
    Nope - that didn't work..
     
  11. rmgolob

    rmgolob Member

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    Oh my - How simple - Thanks!
     
  12. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
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    Location:
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    A limit switch is usually for excess height phleum heat and it will open and shut the system down. Your part number is 175 degree. I don't know what the 30F means. (L175-30F). Some can do both low and high heat to keep the plenum in the correct heat range. On your limit switch with the two blue wires, one comes from the top and the other below to the fan area. I'm suspecting there is another sensor above. there is a condensation pipe coming out of the box and it may be a limit switch for the exhaust temperature.
    If you can post the model number and we can look up the manual and maybe find a circuit diagram or take a picture that is on the unit.


    https://www.lennoxpros.com/25j2601-limit-control-bluewhite-175-deg/p/25J26
     
  13. fitter30

    fitter30 Well-Known Member

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    Location:
    Peace valley missouri
     
  14. fitter30

    fitter30 Well-Known Member

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    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    R to C 24 volts limit is good. W to C with t stat call for heat 24 volts. With 24 volts energize K13,K 109,K3 relays, vent fan runs makes air proving switch powers burner control TH terminal to C. Burner sequence starts.
    With t stat calling for heat check Th to C first then air flow switch if theirs no power. Air flow switch with fan running 24volts to C if not switch is not closed. Air flow switch located just to the left of limit with plastic tubing on it.
     
    Last edited: Dec 2, 2020
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