Solenoid valves play an important role within refrigeration and air conditioning
systems, controlling the flow of refrigerants. Though their base function –
turning the refrigerant flow on and off – is quite simple, this function is key to
ensuring system performance.

Solenoid valves with a spring-loaded plunger or diaphragm may be installed
in any position; however, older-style solenoid valves that utilize a plunger
dependent on gravity to close must be installed with the plunger in an
upright, vertical position.

The most common type of solenoid is the normally closed type. When the
coil is energized, the valve opens. When power is removed, the valve closes.
In a normally open solenoid, the valve closes when power is applied to the
coil and opens when the coil is de-energized.