Final answer:
A pump down control system requires a normally closed liquid line solenoid valve to prevent refrigerant from entering the evaporator when the thermostat is satisfied and the compressor is off.
Step-by-step explanation:
The type of solenoid valve required for a pump down control system is a normally closed liquid line solenoid valve. This type of valve is usually installed in the liquid line before the evaporator. When the thermostat is satisfied, the pump down control system deactivates the compressor, and the normally closed solenoid valve shuts off, preventing any more refrigerant from entering the evaporator.
The compressor continues to run until the low-pressure control senses a reduction in pressure and shuts off the compressor. This prevents refrigerant flood back to the compressor during off cycles.