USCG Exam PracticeRefrigeration cycle and components
After opening a marine refrigeration system for repairs, the engineer evacuates the system to a deep vacuum before recharging. Which of the following BEST states the technical reason for this procedure?
- A. Evacuation raises the system pressure to verify there are no leaks before refrigerant is introduced
- ✓ Evacuation boils off residual moisture so it cannot freeze at the metering orifice or react with refrigerant and oil to form acids and sludgeCorrect
- C. Evacuation purges non-condensable gas that accumulated during operation and would otherwise raise suction pressure
- D. Evacuation cools the compressor crankcase oil to the correct viscosity before the system is started
Why B is correct
The source states that a system opened for repair is evacuated — pumped down to a deep vacuum — specifically 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-condensables is a separate procedure performed on an operating system, not by evacuation after opening.
Cited:NAVEDTRA 14075 §6-6