A container unit's microprocessor-controlled temperature controller is set at 8.9°C, appropriate for a perishable chilled cargo of limes. In this mode of operation, according to the illustrated temperature controller functional diagrams, what should be the operational status of the unit if the actual box temperature is 6.3°C? See illustration GS-RA-35.
• Note that the cargo is perishable chilled, so use the functional diagram labeled for that cargo type on the illustration (not the frozen-cargo diagram). • Focus on how the controller bands are arranged above and below the set point (e.g., modulating cooling, air circulation, heating). Everything on the chart is shown as an offset from the set point in °C. • Convert the actual box temperature to a difference from the set point to see which band it falls into (e.g., within ±0.2°C, between -0.5°C and -1.5°C, etc.).
• Which of the two diagrams (A or B) applies to a chilled perishable cargo like limes, and what operating modes are shown on that diagram? • If the set point is 8.9°C and the actual temperature is 6.3°C, is the box temperature above or below the set point, and by how many degrees? • Looking at the correct diagram, in that temperature range relative to the set point, which mode is shown: modulating cooling, full cooling, air circulation only, or heating?
• Be sure you are using the perishable chilled cargo diagram, not the frozen cargo diagram. • Double-check the temperature difference: set point minus box temperature, in °C, and match that exact range on the vertical scale of the diagram. • Confirm whether the diagram shows cooling, modulating cooling, air circulation, or heating for that specific offset band before you choose your answer.
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