Refrigeration and DX: Diagnose faults using pressures, temperatures, superheat, and subcooling; perform leak detection, recovery, nitrogen pressure testing, micron evacuation/decay testing, charging, component replacement, and nitrogen-purged brazing. Air distribution: Service AHUs, fan coils, VAVs, reheat, exhaust, and CRAC/CRAH equipment; diagnose airflow, static pressure, humidity, coil freezing, and condensate problems; understand economizers and building pressure.