When pressurizing a vessel or component with a mixture of compressed air and halide refrigerant, adding the refrigerant to the system first:

reduces the total quantity of refrigerant required for the test

aids in the dispersion and mixing of the refrigerant throughout the system

minimizes the possibility of the operator missing leaks due to the higher concentration of tracer gas at the start of scanning

speeds the stratification of refrigerant within the test system which increases the reliability of the results