Where should you charge a vapor compression system?

Charging a vapor compression system at the upstream of the expansion valve is necessary to ensure that the refrigerant is introduced into the system effectively. When refrigerant is charged at this point, it allows for proper distribution throughout the system, ensuring that the correct amount of refrigerant enters the evaporator.

By charging upstream of the expansion valve, the refrigerant can flow directly into the low-pressure side of the system, where it is expanded before entering the evaporator. This aligns with the design and operational principles of vapor compression systems, where the refrigerant expands and absorbs heat as it transitions from the liquid phase to the vapor phase.

Charging the system downstream the compressor, at the evaporator, or near the condenser does not provide the optimal flow path for the refrigerant to enter the system. Specifically, introducing refrigerant downstream the compressor could lead to issues such as liquid refrigerant returning to the compressor, which can cause damage. Charging at the evaporator would not effectively get refrigerant into the system for proper operation, and doing this near the condenser would not support the necessary cooling cycle.