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  1. #1
    Join Date
    Apr 2013
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    Portugal
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    18

    RTHA Transition fault

    Hello.

    I need some help on a RTHA 255.

    The unit is triping on BF0 - transition fault. The control goes to A72 (start), the oil resistance contactor goes off, but no signal off compressor start contactors being energized. The control have a pilot contactor and dosent go on in the start. The machine have a oil flowswitch. Already check that flowswitch is open and auxiliary contacts on the run contator are also open.

    All measures i made appointed to the micromodule relay output supply, but i already changed it and the chiller continues to trip on BF0 even without starting the compressor.

    I appreciate any help.

  2. #2
    Join Date
    Jul 2007
    Location
    The Hot South
    Posts
    1,313
    You should call a professional to help you with this.

  3. #3
    Quote Originally Posted by Carlos Daniel View Post
    Hello.

    I need some help on a RTHA 255.

    The unit is triping on BF0 - transition fault. The control goes to A72 (start), the oil resistance contactor goes off, but no signal off compressor start contactors being energized. The control have a pilot contactor and dosent go on in the start. The machine have a oil flowswitch. Already check that flowswitch is open and auxiliary contacts on the run contator are also open.

    All measures i made appointed to the micromodule relay output supply, but i already changed it and the chiller continues to trip on BF0 even without starting the compressor.

    I appreciate any help.
    check your phase monitor, that will cause this.

  4. #4
    Join Date
    Apr 2013
    Location
    Portugal
    Posts
    18
    Tks Traneguy for your reply. I´ve had check it and it was Ok.

    R123 the professional you speaking (Trane technician) said it was from the board.....change it and...same fault. I asked for help on this forum, not to call a tech.

    But, today I have news. The High preassure pressostat (the double one) have one of the contact triped, and strangely the UCM shows BF0 - transition fault.

    So, if someone have a chiller RTHA tripping on BF0, one of the thinks to check is the high pressure pressostat.

  5. #5
    Join Date
    Mar 2005
    Posts
    664
    i had similar call last week
    Keep it simple to keep it cool!

  6. #6
    Join Date
    Nov 2004
    Location
    up in the hizzy
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    1,376
    Quote Originally Posted by Carlos Daniel View Post
    Tks Traneguy for your reply. I´ve had check it and it was Ok.

    R123 the professional you speaking (Trane technician) said it was from the board.....change it and...same fault. I asked for help on this forum, not to call a tech.

    But, today I have news. The High preassure pressostat (the double one) have one of the contact triped, and strangely the UCM shows BF0 - transition fault.

    So, if someone have a chiller RTHA tripping on BF0, one of the thinks to check is the high pressure pressostat.

    Very interesting, thanks for sharing the info! now could you explain whats a "High pressure pressostat"?

  7. #7
    Join Date
    Jul 2007
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    The Hot South
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    Quote Originally Posted by valdelocc View Post
    Very interesting, thanks for sharing the info! now could you explain whats a "High pressure pressostat"?
    And the "Oil Resistance Contactor"?

  8. #8
    Join Date
    Mar 2005
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    664
    Keep it simple to keep it cool!

  9. #9
    Join Date
    Feb 2012
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    EVERYWHERE
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    How does trane diagnosis a bad board over the phone?

  10. #10
    Join Date
    Apr 2013
    Location
    Portugal
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    18
    A Trane Technician went to the unit to diagnosis. He change the board and same tripping code after.

    Sorry, What I want it to say is Oil Heater contactor and High pressure Switch, this one is a double switch, the 2nd one was triped, displaying the BF0 Fault.

  11. #11
    Join Date
    Nov 2004
    Location
    up in the hizzy
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    1,376
    Quote Originally Posted by Carlos Daniel View Post
    A Trane Technician went to the unit to diagnosis. He change the board and same tripping code after.

    Sorry, What I want it to say is Oil Heater contactor and High pressure Switch, this one is a double switch, the 2nd one was triped, displaying the BF0 Fault.
    Thanks once again, so the pressure switch that tripped has a manual reset? and its a dual high pressure safety, protecting 2 separate refrigerant circuits and circuit 2 tripped and after it was re-set the chiller went back to normal, right?
    I'm asking cause I want to learn more about chillers and that particular set up seems unusual.

  12. #12
    Join Date
    Apr 2013
    Location
    Portugal
    Posts
    18
    Yes manual reset, but the 2nd you have to open the box of the switch to reset it, while the 1st one you can simply press the button. The dual high pressure swith is only for 1 idependent circuit (RTHA have only 1 circuit); the mean is if one fail to trigger the other one actuats. Yes after reset it it went back to normal.

  13. #13
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
    2,035
    As I recall, that high pressure switch is actually a single-pole, double-throw switch. The normally closed (NC) contact completes the electrical circuit to the compressor's starter contactor(s) coil(s). The normally open (NO) contact is part of a circuit that generates a diagnostic for high condenser pressure indication and shutdown. Ideally, on an excessive rise in condenser pressure the NC contact opens, and the NO contact closes. The operation of the switch has two results: 1) contactor coil voltage is interrupted, coils are deenergised, and the compressor is immediately shut down, and 2) the input, from the switch NO contacts to the control panel results in a high pressure diagnostic, which leads to a control panel induced shutdown. The redundant function is by design. Now, imagine a very slight, and momentary, rise in pressure that just so happens to occur while operating at the switch's setpoint. The NC contact opens, but the resultant shutdown causes the condenser pressure to rapidly drop before the NO contact can close. The result is a shutdown that the control panel does not initiate. All the control panel "knows" is that suddenly all current to the compressor went away. And it interprets that as a power failure, sometimes as a phase loss. I don't recall the switch itself as being a manual reset. The diagnostics on the panel, yes. But not the switch. Maybe it is different for outside the U.S.? Or maybe I just remember it wrong.

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