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Thread: TEC failure

  1. #1
    Join Date
    May 2012
    Posts
    14

    Hmm TEC failure

    Hi all,
    I have a TEC wich is one of 12 controllers serving chilled water fan coil units with electric heat
    All have common power supply and all on the same FLN
    The TEC in question is showing failed points every morning and upon rest operates fine for the day. I have been able to determine the time of fault and every time it appears to be just before midnight when the scheduler shuts all the plant off for the night
    It would appear from the outside the TEC is not returning from a power failure or FLN failure
    Action so far:
    Replaced TEC with brand new controller, readdressed set application, checked all settings against other controllers - still fails
    Gave TEC its own power supply - still fails
    seperateed FLN from other TEC and ran direct to MBC - still fails
    Not sure what else to try - any suggestions

  2. #2
    Join Date
    Apr 2007
    Location
    Central PA
    Posts
    52
    Is this a new problem? Or since it was new? We had a similar problem but with a MEC there was a dead short feeding into one of the digital inputs maybe something is shorting out when it shuts down

  3. #3
    Join Date
    May 2012
    Posts
    14
    This was an existing fault. Upon taking the site over we had found a relay had been crudly wired in to reset the power supply to the controller. As above we started fresh. replaced the controller with new, re-addressed, etc etc

  4. #4
    Join Date
    Jun 2004
    Location
    Eugene, Oregon
    Posts
    1,018
    Does it fail if you disconnect the fln? Most likely you have a wiring issue with the fln or the temp sensor wiring. If you have faulty wiring between the room temp sensor and the tec it can cause problems similar to faulty fln wiring. Make sure you don't have duplicate addresses on the fln also. Seems strange that it happens at the same time though.

  5. #5
    Join Date
    Nov 2006
    Location
    SE Wisconsin
    Posts
    326
    Put in a tattletale relay in parallel with the TEC power supply. If you get a low enough brownout or quick loss of power the relay will prove it.

    What else is scheduled to start/stop at that time?

    Ken

  6. #6
    Join Date
    May 2012
    Posts
    14
    You can simulate the same failure if you disconenct the FLN or power supply. I have checked the temp sensor and wiring and appears ok, however a sensor fail or wiring fail would most likly be at random times not at shutdown. Have double and tripple checked the addresses

    All the AHU's start and stop at the same time with about one minute intervals between. With the one power supply to all TEC's, even if there was a brown out wouldnt/shouldnt they all reinitiate.

  7. #7
    Join Date
    Jun 2004
    Location
    Eugene, Oregon
    Posts
    1,018
    I have seen similar problems before and it usually turns out to be a wiring issue. Check the Aux temp sensor. I've seen temp sensors wires pinched between the j-box and cover cause some weird problems. One of the TECs having the FLN wire polarity reversed can cause random failures on the FLN. Check the wires to the valve and electric heat.
    You mention that you have 12 TECs on one power supply. That's too many for a single 100VA power supply. Probably not the problem though since you tried a separate power supply.
    Try using a different address. Disconnect the TEC from the FLN, readdress with a different address, delete the old address from the system profile, add a new TEC to the system profile with the new address, reconnect the TEC to the FLN. I have found that sometimes a corrupt database can be the problem and the best way to fix it is to delete and start over.

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