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  1. #1
    Join Date
    Aug 2017
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    Trane FCU troubles

    Hello all,

    I was called out to look at a few Trane fan coil units that are having control issues, and was looking for some help to resolve the issue.

    Model number: BCHD090G200A1F07Z000000BA4FF000000KB0300

    The FCUs are above a ceiling in a large room with computer equipment. There are 4 in total, and the 3 I was asked to look at all stopped working at the same time. The customer informed me that they had been shutting off randomly, so they took it upon themselves to reset them by flipping the breakers on and off. In addition to that, they said there had been power issues in the room previously but didn't call anyone since the computers are all on an UPS system. I am unsure how long this problem has been going on, but that's just a bit of background for you.

    When I looked at the units, all three were idle and waiting for the thermostat to tell them to come on even though the room was around 85F. I then cycled the power to the control boards so I could watch the startup. After a reset the motor control board said there was a signal from the thermostat, but when the fan was ramping up it gave me a fan lockout error. I did not hear the fan or motor even try to start and inspected the motor which looked fine and gave the fan a spin. I went through the same steps with the second and third units, which both gave me the same result.

    This leads me to believe there is an issue with one of the 3 or 4 control boards in the unit. I am by no means a controls technician, so this is where I stopped until I could get assistance. Each unit has its own thermostat and run independently of each other. My train of thought now is that they have dirty power going to the FCUs and that fried the control boards, which I had happen a few years back on some commercial refrigerators.

    Any ideas, opinions, or a point in the right direction would be much appreciated!

    Thanks,
    Kyle

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,792
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    Well, short of ordering new boards for all three fan coils, you could take the board out of the remaining good FCU and put it into one of the others to see if it then starts up.

    Problem there is if that maneuver ends up frying the board, then the computer room has NO cooling and that's bad.

    So a better diagnostic approach is warranted. You said you "inspected" the blower motors. What did that inspection involve? Ohm out the windings? Check for ground? Check shaft for excessive lateral play?

    Is there a current sensor on the motor leads to prove to the control board that the motor is running? If you're getting lockout codes on the board it could be the board is fine but the current sensor is not. Otherwise the fan motors are not drawing amps and the board senses no current draw even with a call for the fan to be on.

    The power issues in the room could possibly be related to dying blower motors. Check everything thoroughly before attempting to change out parts.
    Building Physics Rule #1: Hot flows to cold.


    Building Physics Rule #2:
    Higher air pressure moves toward lower air pressure


    Building Physics Rule #3:
    Higher moisture concentration moves toward lower moisture concentration.

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