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  1. #1
    Join Date
    Oct 2019
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    Furnace fan changing speeds automatically

    I have a Coleman natural gas furnace that was installed in my new house in 2010. It seems I have an issue happening that has stumped my local hvac folks.
    The furnace fan is changing to the cooling speed during the heat cycle on its own. The speed change occurs when the call for heat ends and the flame goes out, at that moment the speed is switching to the faster cooling speed for 30 seconds or so and then switches back to the slower heating speed.
    There are no history codes on the furnace that would indicate an over heat mode. The hvac tech says it should stay on the same speed during the heat cycle for the entire cycle. He’s thinking I might need a new control board. I had a ecobee installed and I’m wondering if that is causing an issue. Any insight on the issue would be helpful before I spend a bunch of money chasing the wrong problem. Thanks.

  2. #2
    Join Date
    Dec 2007
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    Quote Originally Posted by Jb2019 View Post
    I have a Coleman natural gas furnace that was installed in my new house in 2010. It seems I have an issue happening that has stumped my local hvac folks.
    The furnace fan is changing to the cooling speed during the heat cycle on its own. The speed change occurs when the call for heat ends and the flame goes out, at that moment the speed is switching to the faster cooling speed for 30 seconds or so and then switches back to the slower heating speed.
    There are no history codes on the furnace that would indicate an over heat mode. The hvac tech says it should stay on the same speed during the heat cycle for the entire cycle. He’s thinking I might need a new control board. I had a ecobee installed and I’m wondering if that is causing an issue. Any insight on the issue would be helpful before I spend a bunch of money chasing the wrong problem. Thanks.
    Did it start after the Ecobee was installed? If so, I would start there.

    Provide model number of the Coleman furnace.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  3. #3
    Join Date
    Oct 2019
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    7
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    Thread Starter
    Coleman model number TG9S080B 12MP11A

    Ecobee is set to let Hvac control fan.
    System has a fan switch in the hallway to turn on bathroom exhaust and furnace fan.
    Thanks

  4. #4
    Join Date
    Feb 2010
    Location
    Metro Atlanta, GA
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    626
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    Are you using the power extender kit or did you already have a common wire running to the thermostat?

  5. #5
    Join Date
    Oct 2019
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    Thread Starter
    There is a common wire running to the thermostat.

  6. #6
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
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    Did your tech check for any input changes on the board when the speed changed?

  7. #7
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    7,313
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    Are you using a 1" pleated air filter? If so, the furnace may be exceeding the high limit rating and switching to high fan speed. Your tech should measure static pressure.
    AOP Rules: Rules For Equipment Owners.

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    Questions should end with a question mark "?" Statements end with a period "."

  8. #8
    Join Date
    Oct 2019
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    Thread Starter
    Kdean1
    No error codes indicating high limit issue. Is it possible for the furnace to go into a high temp limit without creating a error code? Just a basic merv 8 filter is being used.

    Bame8ez.
    Did not check for board input changes. He did pull the cooling motor lead and when the flame went out the fan quit. This is why the speed is changing. Furnace is switching to cooling as soon as the call for heat ends.

  9. #9
    Join Date
    Aug 2009
    Location
    Beatrice, NE
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    So many questions. Is this 2 stage or single. Was it actually cooling speed or high speed, they are not necessarily the same speed? If you don't know what the input to the board is how do you know what the output of the board should be? What are the chances that the board is kicking up because of high limit and just happens to be shutting down at that moment?

  10. #10
    Join Date
    Oct 2019
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    Thread Starter
    Single stage furnace.
    Can the furnace kick into high limit without throwing an error code?
    The board will show last 5 error codes and there are none.
    Motor leads are black on cool and blue on heat.
    I can ask tech to check board inputs but I’m not sure what that means.

  11. #11
    Join Date
    Dec 2002
    Location
    in a house, Appomattox, Va.
    Posts
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    If the tstat is set to run the fan for x seconds after a heat or cool cycle, that may be the issue.
    Col 3:23


    questions asked, answers received, ignorance abated

  12. #12
    Join Date
    Oct 2019
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    Thread Starter
    I will set it to zero and let you know if that helped. Thank you.

  13. #13
    Join Date
    Dec 2007
    Posts
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    Quote Originally Posted by Jb2019 View Post
    Coleman model number TG9S080B 12MP11A

    Ecobee is set to let Hvac control fan.
    System has a fan switch in the hallway to turn on bathroom exhaust and furnace fan.
    Thanks
    Have they checked into this?
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

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