Question 124Refrigeration & AC - QMED

The correct answer is C) the highest. When all four evaporators of a multi-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 the capacity controlled compressor needs to operate at its maximum capacity to meet the cooling demand of all four evaporators, which requires the highest control oil pressure to fully open the unloader mechanism and allow the compressor to run at its maximum output. The other options are incorrect because A) the lowest control oil pressure would not allow the compressor to meet the cooling demand, and B) the mid-range control oil pressure would not be sufficient to fully open the unloader mechanism. Option D is incorrect because the lube oil system is directly involved in the operation of the unloader mechanism, which controls the compressor's capacity.