USCG Exam PracticeRefrigeration cycle and components
When a refrigeration system is opened for repair and then reassembled, why must it be evacuated to a deep vacuum before recharging?
- A. To verify that the compressor reed valves are seating properly under vacuum conditions
- ✓ To remove all moisture, which would otherwise freeze at the metering orifice and form acids and sludge with the oil and refrigerantCorrect
- C. To purge non-condensable nitrogen used during brazing from the high side of the system
- D. To confirm that the high-pressure cutout is calibrated correctly before refrigerant is introduced
Why B is correct
Moisture is the enemy of any refrigerant system: it freezes at the metering orifice and reacts with oil and refrigerant to form acids and sludge. Evacuation to a deep vacuum boils off all moisture before recharging. While purging nitrogen after brazing is good practice, the source specifically identifies moisture removal as the reason for evacuation.
Cited:NAVEDTRA 14075 §6-6