USCG Exam PracticeRefrigeration and air conditioning
A freezer room evaporator coil is operating normally but space temperature has been rising gradually over several days with no change in compressor run time or suction pressure. Which condition best explains this symptom?
- A. The metering device is overfeeding refrigerant, causing liquid floodback to the compressor
- ✓ Frost and ice accumulation on the coil is insulating the heat transfer surface and blocking airflow, reducing capacityCorrect
- C. Non-condensable air has migrated from the condenser into the evaporator, displacing refrigerant
- D. The high-pressure cutout is set too low, causing the compressor to short-cycle before the space reaches setpoint
Why B is correct
NAVEDTRA 14075 §6-5 describes frost and ice buildup as a universal problem with coils operating below freezing: a layer of frost insulates the coil and blocks airflow, steadily cutting capacity. The gradual nature of the temperature rise over days is consistent with progressive frost accumulation rather than an acute mechanical or refrigerant fault.
Cited:NAVEDTRA 14075 §6-5