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  1. #1
    Join Date
    Jul 2012
    Location
    Southwest
    Posts
    114

    RTWA 090 High Pressure

    I have a Trane RTWA 090 locking out Circuits A and B on high pressure. It has a single Belimo water regulating valve on the condenser water. I replaced the transformer which was way undersized, but it has tripped again.
    The Belimo condenser water valve is controlled by Johnson Contols System 450. Basically, it measures the discharge pressure on both compressors, and then sends a 0-10VDC signal to my Belimo valve to maintain a pressure around 200.
    When I reset the Chiller, both compressors run perfect. The discharge will be 190-200, 95-100 saturated condenser temp, 70-75 suction. Superheat 5-6, everything checks out.
    Has anyone had trouble with a single water regulating valve on a two circuit system?
    the 2nd RTWA090 has had no issues, but it runs with two regulating valves with cap tubes, rather than the single Belimo/Johnson controller.
    The transducers piggyback to the same terminals on the Johnson Control.
    Temporarily, I set the valve manually and unhooked the 24V power supply to the Belimo valve to verify I'm on the right track.
    Can someone explain any potential issues, or what may be happening with my setup?
    My theory is, when it starts to unload, something happens and the condenser water regulating valve shuts. JC, may be set incorrectly, or it may be a flawed design?

  2. #2
    Join Date
    Sep 2008
    Location
    A land down under
    Posts
    315
    [QUOTE=B1978;13972201] 2nd RTWA090 has had no issues, but it runs with two regulating valves with cap tubes, rather than the single Belimo/Johnson controller.
    The transducers piggyback to the same terminals on the Johnson Control.

    I think you are suggesting the control signal (discharge pressure) is being averaged between the two refrigeration circuits ?

    If so, on start up one compressor will start at a time so what is the controller sensing. The RTWA will start the 1st compressor unloaded and run for 180 seconds before step loading approx 30% compressor capacity, if you are controlling to an average 200 psi head pressure setpoint of an operating and non-operating system what is going to happen when the compressor capacity increments? 1st compressor will fault and same sequence can then occur for the 2nd compressor so both lockout. The red light is on the chiller so it is a chiller problem not a control issue.
    Necessity is the mother of invention

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