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  1. #1
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    Mar 2017
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    Struggling to understand Atosa refrigerator control circuit

    I am happy to be working on restaurant refrigerators instead of my usual automotive a/c work. I have a few questions about the Atosa refrigerator control circuit pictured.
    -how does this system decide when to turn the compressor on. It shows a single temp sensor. I did not see any pressure or temp sensor on the evap.
    How could this circuit know when the evap is frozen?
    - It seems like "cabinet heater" and "mullion heater" would run continuously. Am I missing something?

  2. #2
    Join Date
    Jun 2012
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    Northern NV
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    Unless the mfg. has a manual for the operation of this unit, you cannot be sure of why it does anything.

    I'd assume that the case temp is sensed by the thermistor. Unit does not need to know when it is needing defrost as there is not a defrost heater, so apparently this is a box kept above freezing and is "off cycle defrost" flavor.

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  4. #3
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    Mar 2017
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    Thread Starter
    Quote Originally Posted by Juan Madera View Post
    Unless the mfg. has a manual for the operation of this unit, you cannot be sure of why it does anything.

    I'd assume that the case temp is sensed by the thermistor. Unit does not need to know when it is needing defrost as there is not a defrost heater, so apparently this is a box kept above freezing and is "off cycle defrost" flavor.
    I see what you mean. We can only guess that it works with a single temp probe. The two wires shown to the probe make it seem likely it is a thermistor type?
    I wonder if the temp probe is near the top or bottom of the box.

  5. #4
    Join Date
    Jun 2006
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    The temp sensor cycles the compressor when needed. The 2 switches on the left are probably door switches that turn on the light and stop the evap fan when the door is open. The heaters are probably very low wattage door seal heaters and it uses off cycle to defrost. The board might have a hard timer that stops the cycle for x minutes every 4 hours or some time period. It's also possible that the wiring diagram was done by some part time high school kid.

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