🔍 Key Concepts

• Multibox refrigeration systems often cool several cargo spaces using a common liquid line and return, but allow each box to be controlled separately. • Difference between a thermostatic expansion valve (TXV) (controls refrigerant flow based on superheat at coil outlet) and a solenoid valve (on–off valve, can be operated by a thermostat). • Why cooling water regulation or back‑pressure control would affect the whole plant or suction pressure, not each box individually.

💭 Think About

• Ask yourself: in a system with many boxes but one common plant, what kind of control device would let each box turn its cooling on and off independently when its own temperature changes? • Which device on the list is typically controlled directly by a thermostat in the box air rather than by refrigerant superheat alone? • Think about how you would prevent over‑cooling one cargo hold while another still needs cooling — which device can isolate refrigerant flow to just that box?.

✅ Before You Answer

• Identify which option provides individual on/off control to each evaporator or box, not just flow modulation based on superheat. • Eliminate any device that mainly controls compressor suction pressure or condenser/cooling water conditions, since those act on the whole plant, not on each box separately. • Confirm that the device you choose can be electrically operated by a thermostat located in each box, allowing separate temperature settings.