USCG Exam PracticeRefrigeration and air conditioning
After opening a refrigeration system for repairs, what procedure must be performed before recharging the system, and why?
- A. The system must be pressure-tested with nitrogen to verify there are no leaks, because refrigerant vapor is heavier than air and will pool in low spaces
- ✓ The system must be evacuated to a deep vacuum to boil off all moisture, because water freezes at the metering orifice and reacts with oil and refrigerant to form acids and sludgeCorrect
- C. The system must be flushed with the correct refrigerant vapor to purge air, because non-condensable gas raises head pressure
- D. The system must be pre-charged with a small amount of refrigerant to check the sight glass before full charging, because overcharge floods the compressor
Why B is correct
NAVEDTRA 14075 §6-6 and §6-7 establish that moisture is the enemy of any refrigerant system, freezing at the metering orifice and forming acids and sludge. §6-7 specifically states that a system opened for repair is evacuated — pumped down to a deep vacuum — to boil off all moisture before recharging.
Cited:NAVEDTRA 14075 §6-7