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  1. #1
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    Sep 2007
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    RTAA B90 cond temp sensor error

    RTAA 300 machine...

    circuit 2 generating B90 (either when circuit shuts down calls for start) dont know which...

    when resetting the circuit, all starts up ok and controls fans ok... readings at panel match gage and temp readings locally...

    we have changed the temp sensor, compressor module, checked all wiring...

    can anyone speek in depth about the logic that this sensor is involved with.

    this thing is driving me crazy...

    thanks in advance...

  2. #2
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    it is used for condensor pressure conversion, high condensor pressure limit and for controlling the exv and for fan staging.

    manual says the diagnostic is open or short in the wire.

    i have seen many people replace the sensor and instead of replacing the sensor AND the wire, they just cut the wire and wire nut it in at the sensor...got nuts?

    without the sensor installed, the voltage from the 1U5 J4-4,5 should be between 4.975 and 5.025 VDC.

    good luck.
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  3. #3
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    Western Wa
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    I've had numerous episodes of intermittent goofiness with the pin connections at the boards. Mostly on the aux contact wiring, though.
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  4. #4
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    Sep 2007
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    no nuts... we have soldered connections under crimp...

    i will be rechecking the output voltage...

    if that checks i quess we pull new wire...

    i sure wish that they would use a differant style pin connection though...

    thanks guys...

  5. #5
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    Western Wa
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    An ever so slight deflection of every other pin, cleared up a hair-puller-outer for me one time.
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  6. #6
    Join Date
    Sep 2007
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    Bay Area California
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    another thought...

    what if i put in a fixed resistor and tested?... what effect would i have on exv control...

    the main control for the exv is superheat... under what conditions would head pressure (high/low saturated cond temp) override exv logic?...

    thanks...

  7. #7
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    Sep 2007
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    Bay Area California
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    thanks randy s...

    i get it...

    that and a little lube 1 (dielectric grease) wouldn't be bad while were at it...

    i think we will pull some new wire and try the above and see what happens...

    this machine has had cronic problems so i put together a "renew scope of work" (minus compressor rebuilds) to help with a whole host of problems...

    this is the last thing on the list...

  8. #8
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    Quote Originally Posted by chiller rob View Post
    ...the main control for the exv is superheat... under what conditions would head pressure (high/low saturated cond temp) override exv logic?...

    thanks...
    sorry...brain fartage

    the sat cond temp sensor does not directly control the exv...it controls the fans to help maintain enough pressure drop for the exv as well as the pressure to help move the oil. i got a little ahead of myself there...good catch!

    a fixed resistor would be a good test as long as you do not leave it in there...the chiller would not control the cond fans properly. it might turn them all on or it might turn them all off!

    good luck.
    When I am late for work, I usually make up for it by leaving early.

  9. #9
    Join Date
    Sep 2007
    Location
    Bay Area California
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    this particular unit has concrete walls real close to the condenser and has some recirculating going on...

    so i have been having a problem staging fans to begin with as this unit does not have the eprom upgrades...

    we tried to install the eproms but a whole host of comm errors showed up and the only way out was to change out multiple modules...

    so we went back to the original eproms and wired penn pressure controls on the fan contactors in parallel with the compressor modules... we set the pressure controls to work on higher pressures than the ucp...

    so no mater what i can control head...

    as this is a process chiller on startup we were not bringing fans on fast enough...

    what is worse this unit has a bad compressor and the customer cant swallow the cost for replacement so effectively we have an rtaa200...

    speeking of resistors...
    have you ever had to wire a resistor in series with sat cond to effectively lower the condenser temp to keep the smaller compressors (internal oil filters) from tripping on low oil flow diognostic every 30 min? good little trick to keep the unit on line till the coils can be clean or the tubes punched on a rtwa...

    thanks for the feedback jayguy...

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