USCG Exam PracticeRefrigeration and air conditioning
Before recharging a refrigeration system that has been opened for repair, the system must be evacuated to a deep vacuum. What is the primary technical reason for this requirement?
- A. Evacuation purges non-condensable nitrogen used during pressure testing before refrigerant is introduced
- B. Evacuation confirms the integrity of the pressure vessels in accordance with 46 CFR part 54
- ✓ Evacuation boils off residual moisture; water in the system freezes at the metering orifice and reacts with oil and refrigerant to form acids and sludgeCorrect
- D. Evacuation removes excess compressor oil that migrated to the low side during the repair, preventing liquid floodback on startup
Why C is correct
NAVEDTRA 14075 §6-6 identifies moisture as the enemy of any refrigerant: water freezes at the metering orifice and reacts with oil and refrigerant to form acids and sludge. Section §6-6 also states that a system opened for repair is evacuated to boil off all moisture before recharging. Filter-driers are fitted for the same reason.