USCG Exam PracticeRefrigeration principles and systems
Why must a refrigeration system be evacuated to a deep vacuum before being recharged after repair?
- A. To verify that the compressor shaft seal is holding pressure before refrigerant is introduced
- ✓ To boil off all moisture, because water freezes at the metering orifice and reacts with oil and refrigerant to form acids and sludgeCorrect
- C. To purge non-condensable air that has collected in the top of the condenser and receiver
- D. To confirm that the high-pressure cutout and low-pressure cutout are set correctly before startup
Why B is correct
NAVEDTRA 14075 §6-6 states that a system opened for repair is evacuated to a deep vacuum to boil off all moisture before recharging, because moisture freezes at the metering orifice and reacts with oil and refrigerant to form acids and sludge. Purging non-condensable air is a separate procedure performed during normal operation, not specifically tied to post-repair evacuation.
Cited:NAVEDTRA 14075 §6-6