USCG Exam PracticeRefrigeration cycle and components
After opening a marine refrigeration system for repairs, the technician must evacuate the system to a deep vacuum before recharging. What is the PRIMARY reason for this procedure?
- A. To verify that the compressor suction and discharge valves are seating correctly
- ✓ To remove all moisture from the system, preventing freeze-up at the metering orifice and acid formationCorrect
- C. To purge non-condensable nitrogen used to pressure-test the system into the atmosphere
- D. To reduce the head pressure so that refrigerant can be charged from the low side
Why B is correct
Moisture is the enemy of any refrigeration system: it freezes at the metering orifice and reacts with oil and refrigerant to form acids and sludge. Evacuating to a deep vacuum boils off all residual moisture before the system is recharged. Purging non-condensables and checking valve seating are separate concerns and are not the primary purpose of deep evacuation.
Cited:NAVEDTRA 14075 §6-6