Solenoid valves _____?

Solenoid valves play a crucial role in controlling the flow of refrigerant in HVAC systems. They are electro-mechanical devices that open or close refrigerant circuits based on electrical signals. When energized, a solenoid valve typically opens the circuit, allowing refrigerant to flow through. Conversely, when power is removed, the valve closes the circuit, stopping the flow of refrigerant.

Thermostats control the operation of solenoid valves by sending electrical signals based on temperature settings. Thus, solenoid valves can indeed be activated by a thermostat, contributing to the overall control of the HVAC system's cooling or heating processes.

Given these functions, it is accurate to say that solenoid valves both open and close refrigerant circuits and can be activated by a thermostat. This comprehensive functionality supports the conclusion that all the listed roles of solenoid valves are correct.