What role does the expansion valve play in a heat pump system?

The correct role of the expansion valve in a heat pump system is to control the flow of refrigerant to the evaporator coil. The expansion valve operates by reducing the pressure of the refrigerant, which allows it to expand and cool before it enters the evaporator. This is crucial because the lower pressure and temperature of the refrigerant enable it to absorb heat effectively from the indoor environment during the heating cycle.

Controlling the flow also ensures that the refrigerant does not flood the evaporator or starve it, which is vital for maintaining the system's efficiency and preventing damage. By precisely regulating how much refrigerant enters the evaporator coil, the expansion valve helps maintain optimal system performance and temperature control in a heat pump system.

This function is distinct from other components of the system; for instance, increasing the pressure of the refrigerant is typically performed by the compressor, not the expansion valve. Additionally, moisture removal from the refrigerant is handled by components such as the dryer, while mixing refrigerant with air does not occur in the function of the expansion valve.