In a dual capacity system, what mode must the units be operating in for charging or refrigerant checking?

In a dual capacity system, the units must be operating in high-speed mode for charging or refrigerant checking because this mode allows for a greater flow of refrigerant through the system. When operating in high-speed mode, the compressor's output is maximized, ensuring that the system is working under conditions that are representative of typical operation. This is crucial for properly monitoring and adjusting refrigerant levels, as it leads to a more accurate assessment of the system’s performance and efficiency.

Moreover, charging the refrigerant in high-speed mode helps in preventing any potential issues that could arise from insufficient refrigerant flow, which might not be evident if the system is running in low speed or in heating mode. Checking refrigerant levels while in a mode that does not require maximum refrigerant flow, such as cooling or low speed, could result in incorrect readings and affect the system’s overall performance.