1. Air leaks into low-pressure systems
Excessive purge operation can indicate air infiltration. Controlled hot water or a built-in pressurization device is preferred for leak testing; nitrogen is a controlled second option.
2. Recovery and freeze protection
Recover liquid first, then vapor. Circulate or remove water during evacuation so falling pressure and temperature do not freeze water in the tubes.
3. Oil handling
Heat oil to about 130°F before removal to drive off dissolved refrigerant and reduce emissions.
4. Recharging
Introduce vapor before liquid to reduce freezing risk and use the evaporator charging valve according to the manufacturer's procedure.
5. Purge units
Purge units remove noncondensables. High purge time is a symptom to investigate, not a normal substitute for leak repair.
6. Room safety
Low-pressure equipment rooms require oxygen-deprivation protection. R-123 systems also require refrigerant detection under applicable ASHRAE safety provisions.