When charging an R-410A system with a capillary tube, what method should be used?

Charging an R-410A system with a capillary tube typically involves utilizing the superheat method. This approach is critical because capillary tubes are fixed metering devices that do not allow for adjustment of the refrigerant flow. Therefore, it is essential to ensure that the evaporator is receiving the correct amount of refrigerant to achieve proper system operation.

The superheat method involves charging the system until the desired level of superheat is reached at the evaporator outlet, which indicates that all the refrigerant in the evaporator has evaporated and only vapor enters the compressor. This method helps prevent liquid refrigerant from returning to the compressor, which could cause damage.

The other options, such as pressure charging, subcooling, and temperature testing, are not optimal for systems with capillary tubes. Pressure charging could lead to overcharging or undercharging without the feedback provided by superheat measurements. Subcooling focuses on the liquid refrigerant in the condenser, and while it's essential for other metering devices, it isn't as applicable for capillary tube systems. Temperature testing is typically used to ensure that the system operates within the desired temperature ranges, but it doesn’t provide the direct feedback necessary for charging the system properly.

Thus, utilizing superheat when