Which controls are typically used in an automatic pump-down system?

In an automatic pump-down system, the primary goal is to maintain an appropriate level of refrigerant in the evaporator while preventing any liquid refrigerant from entering the compressor during off cycles. This is achieved primarily through the control of the liquid line solenoid and the compressor using a low pressure switch.

In this configuration, when the pressure in the evaporator drops below a certain threshold, the low pressure switch activates. This switch deactivates the compressor, which in turn lowers the refrigerant pressure in the system, causing the liquid line solenoid to close. By doing so, the system effectively pumps the refrigerant out of the evaporator and prevents it from returning to the compressor, ensuring that the compressor runs without risking damage from liquid refrigerant.

The thermostat’s role is to monitor the temperature within the space being cooled and act as an intermediary that turns on or off the liquid line solenoid based on the temperature needs. When the building is demanding cooling, the thermostat allows the liquid line to open and the compressor to operate, but if the space reaches the desired temperature and the pressure drops, the mechanisms controlled will pump down the refrigerant appropriately.

This systematic coordination between the thermostat and the low pressure switch is essential for the efficient functioning of an automatic pump