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Thread: Fan keeps running after T-stat is satisfied

  1. #1
    Join Date
    May 2021
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    Fan keeps running after T-stat is satisfied

    I am having issues to figure out what could be wrong with this AC system. My friend said that indoor fan keeps running and it doesn't stop after T-stat is satisfied. She even sent me a picture of T-stat showing fan on auto, room temperature at 77 and set point at 79. She said that at that point fan was still running.
    Of course, when I was checking the unit, I made sure that fan is in auto, but I could not witness this intermittent issue she was describing. Her saying that fan keeps running made me think on few things:
    1. maybe fan wire is touching somewhere a red wire and is being energized regardless of T stat command
    2. Maybe fan relay coil or time delay relay that green wire from T stat is connected to is intermittently getting stuck
    3. Maybe thermostat is bad.

    I pulled the thermostat off and measured voltages between common wire and every terminal. I got 0 V everywhere, except with the red wire (24 V), just as it should be. This step was telling me that at the time of me checking T-stat wires were good and not shorted. Considering that picture she sent me is showing room temperature lower than the setpoint, that means that not only fan is running after T-stat is satisfied, but also is compressor as cooling is provided. In my experience only one component is controlling both compressor and indoor fan at the same time and that is a T stat. This is why I replaced it. Today she said that fan kept running again when it wasn't supposed to. Of course when ever i checked the unit fan would come on when called for (after time delay) and would shut off when called for (also after time delay). I told her I could also replace the time delay relay and indoor fan relay, but I keep thinking if compressor keeps running as well (and that theory is based on lower room temp that cooling setpoint), I don't see the point replacing these relays. Am I missing something? Is there anything else that could produce these symptoms? Any advise is appreciated. Thank you.

  2. #2
    Join Date
    Mar 2009
    Mount Holly, NC
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    Is there a zone system?
    It sounds like you have checked things, we cannot assist with repairs on this forum, sorry.

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