An automatic pumpdown system requires a

• A. Relief valve
• B. Liquid line solenoid
• C. Pressure switch
• D. Manual isolation valve

Answer: (B)

Automatic pumpdown relies on an electrically operated valve in the liquid line to isolate the evaporator at the end of a cooling cycle. The liquid line solenoid closes to stop liquid refrigerant from returning to the evaporator, pumping the refrigerant into the condenser/receiver and leaving the evaporator drained. This minimizes the refrigerant charge in the evaporator when the system shuts down and makes startup more efficient. When a new cooling cycle starts, the solenoid opens again to allow liquid to reach the evaporator. The other options serve different safety or control roles and do not automate the isolation of the liquid line.