Solenoid valve
Also known as: electric shut-off valve
Short definitionA valve that opens when its coil is energised and closes by spring when the power is cut. In the liquid line it shuts off refrigerant to the evaporator; pump-down control and multi-room systems depend on it.
When the coil is energised, the magnetic field lifts the plunger and the passage opens. When the current is cut, a spring pushes the plunger back and the valve closes. In a cold room it usually goes in the liquid line, ahead of the expansion valve. When the room reaches the required temperature, the thermostat closes the solenoid and no refrigerant flows to the evaporator.
In a pump-down arrangement, once the solenoid closes the compressor draws the remaining refrigerant out of the evaporator and collects it in the receiver, and the low-pressure switch then stops the compressor. No liquid reaches the compressor at the next start. Where several rooms share one condensing unit, each room gets its own solenoid. The arrow on the body shows the flow direction. Coil voltage must match the panel, and a high-temperature type is chosen for hot gas defrost lines.