Refrigeration & Air Conditioning USCG Question #192 (Set 4)

During operating periods of a multi-box refrigeration system using a capacity controlled compressor, when all of the evaporators of a four box plant are actively being fed with liquid refrigerant, the control oil pressure acting on the hydraulic relay piston will be at what value?

Official USCG Answer & Rule Citation

Correct Answer: Option C — the highest

When all evaporators demand refrigeration, suction pressure rises and acts on capacity controls, maximizing the hydraulic relay piston oil pressure to keep all compressor cylinders loaded.

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