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Thread: Emerson KCJ450LAL compressor thermal shut-off issue

  1. #1
    Join Date
    Jan 2020
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    Question Emerson KCJ450LAL compressor thermal shut-off issue


    I'm working on a Sanyo -80 Deep Freezer Cascade System.
    Capacity: 750Liters
    Ambient Room Temperature: 23-27degree Celcius
    First Stage/High Stage Compressor: KCJ450LAL : R404A gas
    Second Stage/Low Stage Compressor : KCJ450LAL : R508B gas
    Metering device: Capillary tube

    Cascade temperature when Second stage/Low Stage is off: -47degree Celcius
    Cascade temperature when Second stage/Low Stage is ON: -36degree Celcius

    Now, the issue faced by me is that, the second stage/low stage compressor starts and after around 45mins to 1hr of running it shuts down. It is an internal thermal cut-off. I've checked the relay that powers the compressor and it stays ON but because of excessive internal heat it shuts down. Again after it cools down (takes about 1hr to 75mins), the compressor starts.

    From Room Temperature to -80degree C it takes about 16 hours due to compressor shutting down because of thermal cut-off.

    I suspected an airflow issue and have installed an additional fan to cool the compressor, but it is of not much use except compressor now gets cooled 15mins quicker than before after shutting down due to over heating.

    Suction pressure when the chamber is at -65 degree Celcius: -6 inches of Hg
    Return gas temperature 4inches from compressor: 25degree Celcius

    I'm confused as to why this is happening because the system does achieve -80degree Celcius temperature after several cycles of OFF and ON due to heating. But I'm afraid this may result in a premature compressor failure and I'll have to attend to an unhappy customer.

    Any inputs/suggestions please? as to why this is happening?


  2. #2
    Join Date
    Mar 2015
    Medford, N.Y.
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    2 temps needed. Superheat 6" before comp and Discharge Line temp 6" after comp.

  3. Likes crazzycajun liked this post.
  4. #3
    Join Date
    Apr 2015
    Kent, OH
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    the compressor usually gets cooled by the refrigerant coming back through the suction line. the superheat and discharge temp will be important for troubleshooting. also a quick thing you can check is if the suction line feels cold. if the suction line is not cold to the touch where it enters the compressor then you're probably not getting cold enough refrigerant vapor back to the compressor to keep the motor cool. that could be caused by a low refrigerant charge but you would need the other info to make that determination.

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