USCG Exam PracticeRefrigeration and air conditioning
After opening a refrigeration system for repair, the engineer evacuates the system to a deep vacuum before recharging. What is the primary technical reason for this procedure?
- A. To verify there are no leaks in the system before introducing refrigerant
- ✓ To boil off all residual moisture, preventing freeze-up at the metering orifice and acid formationCorrect
- C. To purge non-condensable air that would otherwise raise the high-side operating pressure
- D. To return residual oil from the evaporator and piping back to the compressor crankcase
Why B is correct
NAVEDTRA 14075 §6-6 and §6-7 identify moisture as the enemy of any refrigerant system. §6-7 specifically states that a system opened for repair is evacuated to a deep vacuum to boil off all moisture before recharging, because water freezes at the metering orifice and reacts with oil and refrigerant to form acids and sludge. While leak checking and air purging are valid practices, the primary stated reason for deep evacuation after opening is moisture removal.
Cited:NAVEDTRA 14075 §6-7