When charging liquid should be added to the side of the compressor?

When charging a refrigeration or air conditioning system, liquid refrigerant should be added to the side of the compressor only if the system is designed for liquid charging and the compressor is equipped to handle it. This typically occurs when the compressor is off and the system is under the correct conditions, ensuring that the liquid can be effectively vaporized in the evaporator. It's important to follow manufacturer guidelines and safety protocols to avoid damage to the system or compressor. Always ensure the system is properly evacuated and charged to the correct specifications.