How do you charge R138 in a commercial refrigerator?

To charge R138 in a commercial refrigerator, first ensure the system is off and properly evacuated to remove any old refrigerant. Connect the R138 refrigerant cylinder to the service port on the low-pressure side of the system. Open the cylinder valve and allow the refrigerant to flow into the system, monitoring the pressure gauges to avoid overcharging. Once the desired charge is achieved, close the cylinder valve, disconnect the hoses, and run the system to check for proper operation.