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  1. #1
    Join Date
    Jul 2007
    Location
    New Jersey
    Posts
    3,031

    blower wont shut off

    friend of mine had to replace his ignition module on Lennox unit model # G20Q3E-75-4

    the original module was SP745 robert shaw
    the replacement part they gave him is also Robert shaw 80-845

    he said he went wire for wire but he said the blower wont shut off even disconnecting tstat, the blower stays runnin. I havent been there ...Im just throwing this out here to see if anybody knows if it could be MODULE related. I told him to check contactor to see if its stuck in. But not being there, i couldnt really say much else.
    “If I have seen further than others, it is by standing upon the shoulders of giants.” ~ Sir Isaac Newton


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  2. #2
    Join Date
    Jul 2007
    Location
    New Jersey
    Posts
    3,031
    mistake....new module is 780-845
    “If I have seen further than others, it is by standing upon the shoulders of giants.” ~ Sir Isaac Newton


    I'm learning all the time, the tombstone will be my diploma!!!


    Did you ever stop to think, and forget to start again?

  3. #3
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,514
    Was the blower runnign constant with the old module?
    Look really close at the limit switches/connections, some modules will run the blower when a limit opens up.

  4. #4
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,936
    Quote Originally Posted by Tommy1010 View Post
    blower wont shut off
    friend of mine had to replace his ignition module on Lennox unit model # G20Q3E-75-4
    If your friend accidentally crossed the "W" and "limit" wires on the BCC2 control board, it will cause the fan to run continuously.
    Instead of learning the tricks of the trade, learn the trade.

  5. #5
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,765
    ignition module has NO control over fan operation. fan is controlled by blower control board.
    if limit switch is open fan will run constantly and no power will be supplied to thermostat or ignition module.

  6. #6
    Join Date
    Sep 2003
    Posts
    1,677
    Nope

    No Fan Control

    Tell him to follow the voltage.....
    ++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++


    When the thermostat calls for heat, the 780-845 control simultaneously initiates ignition sparking and opens the pilot valve portion of the gas valve. Pilot flame recognition stops ignition sparking and opens the main valve portion of the gas valve. Pilot burner flame is continuously monitored at a synchronous frequency for the duration of the heating cycle. Should the pilot flame fail during the heating cycle, the control will shut off the main valve until the pilot flame is established.
    The 780-845 lockout ignition control provides 90 seconds of spark, followed by a 6 minute time delay (purge) between ignition attempts. After three tries, if no pilot flame is sensed, the control goes into a one-hour lockout period. At the end of the lockout period, if the demand for heat is still present, the unit will repeat the three tries for ignition.

    During lockout, you may override the auto-system, and manually reset the unit at the thermostat. The green diagnostic LED will be on continuously for normal operation. The LED will be off for internal lockout and will flash continuously for problems external to the control (ie. not sensing flame).

  7. #7
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,936
    Another thought - has this G20 unit been modified with the OPTIONAL "Continuous Fan" switch?

    If it has, and your buddy is familiar with the BCC2 control board, and capable of troubleshooting SPDT switches, I would have him check that also.

    If you are heading over to look at the unit, let me know, and I will get a manual with wiring diagrams off to you via email.
    Instead of learning the tricks of the trade, learn the trade.

  8. #8
    Make sure you check the heat exchanger

  9. #9
    Join Date
    Dec 2010
    Location
    WV
    Posts
    115
    Now this is why i like this site...VERY good information....

  10. #10
    Join Date
    Sep 2012
    Location
    New York
    Posts
    175
    I agree, I suspect a bad control board if the blower is running constantly. Does he have a himidifier? I know with the aprilaire 400 they want you to wire it in such a way that it humidifies even without the system calling for heat. Simple fix but just make sure you checkout everything befor condemning parts. Let us know how it turns out.

  11. #11
    Join Date
    Sep 2012
    Location
    thomaston, ct
    Posts
    334
    We are Lennox dealers, I find bad hi limit switches often that cause this issue. With the furnace cool, check the high limit. I replace oil high limit switch with Texas Instruments brand much better luck with them.

  12. #12
    Join Date
    Jan 2013
    Location
    Mistake by the lake
    Posts
    34
    Lennox started using a universal board a short time ago and sending four different wiring harnesses to replace on the different furnaces. I had to replace a board on a g61 and the original board used 11 of the 12 pins on the mullinex. New board used all 12. Blower always ran till I figured out the old harness wouldn't complete the limit circuit. Changed harness and shagged a$$ outta there

  13. #13
    Join Date
    Feb 2010
    Location
    Calgary, Alberta
    Posts
    1,157
    Why were you given a WR control for that furnace?
    Should be a black honeywell, 30w33 is the part number from Lennox. The directions make this a brainless swap out.
    Comes with a new flame sensor and ignition wire among other things.

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