USCG Exam PracticeRefrigeration and air conditioning
A freezer room evaporator coil is operating normally but the refrigerated space temperature is rising steadily over several days despite no change in compressor operation or refrigerant charge. The most probable cause, and the correct corrective action, are:
- A. Non-condensable air in the condenser; purge the condenser and receiver to restore high-side pressure
- ✓ Frost and ice accumulation on the evaporator coil insulating it and blocking airflow; defrost the coil on scheduleCorrect
- C. Overcharge of refrigerant flooding the compressor suction; recover excess charge to restore superheat
- D. A blocked condensate drain on the evaporator; clear the drain to restore dehumidification capacity
Why B is correct
NAVEDTRA 14075 §6-5 states that coils operating below freezing accumulate frost and ice that insulate the coil and block airflow, steadily cutting capacity, and that freezer coils must be defrosted periodically. A gradual rise in space temperature over days with no other system change is the classic presentation of progressive frost buildup, not an acute refrigerant or condenser fault. Blocked condensate drains apply to above-freezing air conditioning coils, not freezer coils.
Cited:NAVEDTRA 14075 §6-5