What is the primary function of solenoid valves in HVAC systems?

The primary function of solenoid valves in HVAC systems encompasses all the options listed, making the most comprehensive response correct. Solenoid valves are electromechanical devices that act as switches to control the flow of refrigerant or other fluids within a system.

When activated, these valves can open or close the refrigerant circuit, allowing or blocking the flow of refrigerant to various components such as evaporators or condensers. For example, when the system needs to cool, the thermostat sends a signal that energizes the solenoid valve, allowing refrigerant to flow through the system. Conversely, when the desired temperature is reached, the valve can close, stopping the refrigerant flow and thus terminating the cooling process.

This dual capability of opening and closing circuits, alongside their activation based on signals from the thermostat, encapsulates their essential role in HVAC systems for regulating temperature and ensuring efficient operation. Thus, recognizing solenoid valves' multifaceted functions strengthens an understanding of how HVAC systems operate.