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  1. #1
    Join Date
    Jun 2011
    Posts
    6

    blower motor runs constantly

    I've recently went to a call where the blwr mtr runs nonstop. Its an old 90% Carrier furnace. I pulled the Tstat off the subbase, disconnected the wire off the G terminal on the Tstat, but the motor continued to run. I concluded that the relay on the circuitboard was stuck closed. I replaced the circuitboard, but its still doing the same thing. There's no fan limit control on this furnace, so ii really dnt know What else it could be. Can someone help?

  2. #2
    Join Date
    Aug 2011
    Location
    Stamford, CT
    Posts
    44
    Some times if the hi limit switch is open or any other safety switch on the heating circuit is open the board will keep the fan running on some boards don't no about carrier specifically. Also check to make you have the fan wired correctly.

  3. #3
    Join Date
    May 2011
    Location
    Ripley, WV
    Posts
    1,132
    Sounds like a limit or safety is open, or a wire is off of one of them. Check that safety circuit out and I imagine you'll find it.

  4. #4
    Join Date
    Jul 2010
    Location
    Vegas
    Posts
    59
    I agree with the past two responses as well.

    A dirty plugged filter can sometimes cause this, as well as a filthy unit. I think i had that happen years ago, unit was filthy, dirty filter,
    probably coil dirty too, then they set the temp high, and it trips the limit, and limit was so dirty that if and when it reset, it didn't make
    contact. So it kicks the fan on in "safety" mode to cool it down... until the limit resets.

    We are assuming this is not an ECM motor since you said there's a relay on the circuit board. Correct?

  5. #5
    Join Date
    Feb 2004
    Posts
    2,457
    Four items put DNP products into continuos fan and no heat
    1-bad transformer 2-open limit/rollout switch 3-open fuse link 4- bad board

  6. #6
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    3,959

  7. #7
    Join Date
    Jun 2011
    Posts
    6
    The blower motor runs nonstop with the tstat turned to the off position

  8. #8
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,020
    How about model and serial #?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,808
    Do you have a senior tech that can go with you to this service call.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Mar 2013
    Location
    Palm Desert CA
    Posts
    107
    I had an old carrier fau last week. Fan was running constantly on med speed. Turned out to be a bad transformer. No power to the board.

    Sent from my HTC One using Tapatalk 4

  11. #11
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    3,959
    Quote Originally Posted by garageink View Post
    I had an old carrier fau last week. Fan was running constantly on med speed. Turned out to be a bad transformer. No power to the board.

    Sent from my HTC One using Tapatalk 4
    How did the fan relay engage if there was no power to the board?

  12. #12
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    3,959

    Carrier schematic

    If anything in the yellow path is open it will give a 33 fault code nd run fan/inducer. Is the inducer running on the system you are testing?
    Attached Images Attached Images  

  13. #13
    Join Date
    Mar 2013
    Location
    Palm Desert CA
    Posts
    107
    I haven't a clue. I was scratching my head, called the boss and he told me to change the transformer and pow! Worked like a charm. The wiring diagram had turned to yellow dust long before. So I can't confirm or deny how it worked.

    Sent from my HTC One using Tapatalk 4

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