USCG Exam PracticeRefrigeration cycle and components
The suction pressure on a reciprocating refrigeration compressor will not pull down, and head pressure will not build to normal operating levels. Cooling is poor. Which condition BEST explains all three symptoms together?
- A. A plugged filter-drier restricting liquid flow to the expansion valve
- B. An undercharge of refrigerant causing the low-pressure cutout to short-cycle the compressor
- ✓ Broken compressor valves preventing the machine from compressing vapor effectivelyCorrect
- D. Non-condensable air trapped in the condenser raising head pressure above normal
Why C is correct
Broken compressor valves result in a suction pressure that will not pull down and a head pressure that will not build, with little cooling — the compressor cannot develop differential pressure across the system. A plugged filter-drier would show low suction but normal or low head; undercharge shows low suction and low head but the compressor still develops some differential; air in the system raises, not lowers, head pressure.
Cited:NAVEDTRA 14075 §6-8