In which mode of operation is the heat pump charged when determining the correct subcooling value?

The heat pump is charged in cooling mode when determining the correct subcooling value because this mode allows the refrigerant to fully condense and cool before it enters the metering device. In cooling mode, the system is designed to remove heat from the indoor environment and discharge it outside, which establishes a specific set of pressures and temperatures that are essential for calculating the subcooling.

Subcooling refers to the process of cooling the refrigerant below its condensation temperature at a given pressure, ensuring that only liquid refrigerant enters the expansion device. Properly managing subcooling helps in optimizing the efficiency of the heat pump and preventing issues such as compressor damage due to the presence of vapor refrigerant.

In contrast, heating mode operates under different conditions that may not reflect the accurate subcooling requirements, as the refrigerant flow and state change are primarily aimed at extracting heat from the outdoor environment, rather than allowing for proper cooling and condensation of the refrigerant. Therefore, using the cooling mode for charging ensures that measurements taken are relevant and aligned with the operational characteristics of the system for efficient performance.