🔍 Key Concepts

• Economizer circuit operation in a refrigerated container: when the ESV (economizer solenoid valve) opens vs stays closed, and how that affects system capacity and subcooling. • Compressor unloading: what the unloading solenoid valve (USV) does to the compressor capacity when it is energized/open or de‑energized/closed. • Effect of load conditions: box temperature only slightly above set point and low ambient temperature on whether the system wants maximum or reduced cooling capacity.

💭 Think About

• Under low ambient temperature and only a small difference between box temperature and set point, is the system under heavy load or light load? How does that influence whether you want extra capacity from the economizer or not? • Think about what happens when the unloading solenoid is energized: does that increase or decrease the number of active compressor cylinders (and thus capacity)? Which condition is more stable when you are close to set point? • Use the diagram text: the economizer is described as increasing system capacity and efficiency. In the situation given, is there a need to increase capacity, or to back it off to prevent short cycling or overshooting the set point?

✅ Before You Answer

• From the legend/description, verify which valve state (energized/open vs de‑energized/closed) corresponds to economizer in operation and which corresponds to it being bypassed. • Confirm from your notes whether unloading means reducing the compressor’s active cylinders (and therefore reducing capacity) when that solenoid is open or closed. • Before choosing an answer, match the operating condition (light vs heavy load) to a logical combination: economizer on/off and compressor at full/reduced capacity, then pick the option whose valve states produce that combination.