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  1. #1
    Join Date
    Jan 2013
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    Fan limit switch

    My rooftop electric package system is turning the fan on and it won’t turn off. I’ve disconnected the green wire from the thermostat and the fan still turns on (heat and cool are off). I tested both fan limit switches for continuity and they’re ok. The ohms are about 1.6 on the continuity setting but reads about .7 on the ohm function setting. Are these switches ok or can they malfunction even though the continuity is good. Thanks for any help...

  2. #2
    Join Date
    Mar 2015
    Location
    Medford, N.Y.
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    Maybe a Fan relay?

  3. #3
    Join Date
    Sep 2002
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    Virginia
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    Quote Originally Posted by bugstein View Post
    I tested both fan limit switches for continuity and they’re ok. The ohms are about 1.6 on the continuity setting but reads about .7 on the ohm function setting. Are these switches ok or can they malfunction even though the continuity is good. Thanks for any help...
    Fan limit switches were used back in the day ... on gas furnaces

    Where are these switches you are testing located ?

    Do they only have about 26 volts going through them ? Or 120v , or 220 volts

  4. #4
    Join Date
    Jul 2013
    Location
    Richmond, VA
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    Doubt you have a fan limit switch on a package unit, but I would be looking more closely at the fan relay/board or motor module if it’s an ECM.

  5. #5
    Join Date
    Aug 2009
    Location
    Beatrice, NE
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    If this is electric heat you could have a stuck sequencer leaving an element and the fan on. The element may have burnt out so only the fan is running.

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  7. #6
    Join Date
    Aug 2002
    Location
    Southold, NY
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    When was the last time this unit was professionally serviced?

  8. #7
    Join Date
    Jan 2004
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    PA
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    Moved to AOP.
    Contractor locator map

    How-to-apply-for-Professional

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

  9. #8
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    Jan 2013
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    Thread Starter
    I’m not a tech—so not sure how to check that. Is it possible the switches are bad even though they have continuity ??

    The units about 20 years old. The two switches are labeled 165F—40. One appears to be for the hotbox and the other I guess for the AC. I’m not a tech—is ECM “electronic control module”. ??

    Couple years ago

    How do I check that ??

    On the back panel. Haven’t tested them with the power on—kind of scary to reach in with my meter...
    Last edited by beenthere; 03-18-2020 at 08:12 PM.

  10. #9
    Join Date
    Aug 2002
    Location
    Southold, NY
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    First you need to check as there opening / closing. Tough to do. Please get a qualified contractor on site!

  11. #10
    Join Date
    Jan 2004
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    PA
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    Sorry, this is not a DIY site.

    Call a service company out to fix your unit.

    Thread closed.
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