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  • air handler fan keeps running

    Originally posted 6-24-2015 3:57 PM
    By: biguglydish

    It`s Trane -2tee3f31a1000aa. Just had variable speed motor controller replaced to get the fan running again but now this fan just keeps running nonstop. The unit cycles on and off according to the temperature setting but again it just keeps running. Turning tsat off didn`t do a thing and only way to stop it is to shut the power off. Is it a tsat that`s bad or is it a control board, or what ?? Just cost me arm and leg to replace the motor controller so someone out there please help me to troubleshoot this so as to save my torso. Thanks much !

  • #2
    Originally posted 6-24-2015 10:01 PM

    first, check the fan switch on your thermostat. It should be on AUTO. if it's on 'ON' then it will always run.

    Second, make sure you have the correct part. A 1 letter/number difference in the part number can make it not compatible with your system and could cause damage.

    Third, make sure it is set up correctly. There may be jumpers or dip switches to configure the board for your type of setup. HVAC is not intended for the do-it-yourself repair and you may not have access to all the manuals for your system. Also, replacement parts are sold and packaged with the assumption that you have the knowledge and training to set it up. Some complex systems require a programmer to set the controller up.

    Fourth, make sure it's wired correctly. The G wire from the thermostat is your fan control *in a BASIC system*. If your system has a special thermostat to work with your system then you may have a different or multiple fan control circuits. (outlined in the manuals) If it's basic, label and disconnect the wire from your handler's G terminal and test. If it stops, then the issue is in your thermostat. If it still runs, try labeling and disconnecting all the wires from your thermostat

    If the above doesn't work then it's time to call someone out.


    • #3
      Originally posted 6-29-2015 4:42 PM
      By: biguglydish

      Thanks Mr T for your input.

      I decided to have this issue addressed by a local heat & cooling company that replaced variable speed motor controller. The technician said there is nothing wrong with tsat and that it had to be control board that needs replaced. After replacement, strange thing happened that did not before. In cooling mode when outside fan stops , the inside fan stops s​imultaneously, whereas before the inside fan usually stopped about 4 or 5 minutes later. Also when the fan is idle, pressing fan-on on tsat do not turn on the fan. The inside fan only works when the unit kicks into cooling mode. The technician recommended yet another new board replaced so he did and still no go. He is at a loss as to what he can do next. He said all the appropriate voltages are measured across the circuit and he is still in


      • #4
        My blower was coming on with no thermostat wires connected. After having a pro with a trainee tell me he thought it was a bad transformer, I noticed a bad resistor on the board. I replaced the board, cleaned the evaporator coils and checked all I knew to check.
        Got her going.

        btw, from my research, a bad contractor on the ac unit can cause damage to a board. I left the the thermostat wires going to the contactor off for this reason scared it would damage the board I put in. I will repair the ac unit between now and spring.
        Did you get this one figured out?
        Mine sat for like 3 years!
        I am keeping an eye out in the inducer motor.
        Oops! Just now noticed the date on this post.
        But, would still be interested in knowing the fix.

        Last edited by boman11; 01-14-2020, 07:11 PM. Reason: Just now noticed the date.