Question 3Refrigeration & AC - 1st Asst/Chief

The correct answer is C) the highest. When all the evaporators of a four-box refrigeration system are actively being fed with liquid refrigerant, the control oil pressure acting on the hydraulic relay piston will be at its highest value. This is because as the refrigeration load increases with all evaporators in use, the compressor capacity control system will need to increase the compressor displacement to meet the higher demand. This increase in compressor displacement requires the control oil pressure to be at its maximum to ensure the hydraulic relay piston is positioned to allow the compressor to operate at its highest capacity. The other options are incorrect because the control oil pressure would not be at its lowest (A) or mid-range (B) when the refrigeration load is at its highest, and the lube oil system is indeed relevant to the operation of the capacity control unloader (D).