USCG Exam PracticeRefrigeration cycle and components
A marine refrigeration plant shows low suction pressure, low head pressure, bubbles in the sight glass, and frost forming only partway along the evaporator coil. Which condition BEST explains all of these symptoms together?
- A. Non-condensable gas (air) trapped in the condenser
- ✓ Refrigerant undercharge or a system leakCorrect
- C. Expansion valve stuck in the open position
- D. Fouled condenser tubes with reduced seawater flow
Why B is correct
Low suction pressure, low head pressure, bubbles in the sight glass, poor cooling, and partial frost on the evaporator are the classic symptom set for refrigerant undercharge or a leak. Air in the condenser and fouled tubes raise head pressure, not lower it. A stuck-open expansion valve causes flooding and slugging, not low pressures on both sides.
Cited:NAVEDTRA 14075 §6-8