USCG Exam PracticeAir conditioning, ventilation, and compressed air
A freezer room evaporator coil has accumulated a heavy layer of frost. What is the direct operational effect of this condition on system capacity?
- A. The frost layer increases the surface area of the coil, temporarily improving heat transfer.
- ✓ The frost layer insulates the coil and blocks airflow, steadily reducing capacity.Correct
- C. The frost layer causes the metering device to overfeed refrigerant, flooding the compressor.
- D. The frost layer raises suction pressure, causing the high-pressure cutout to trip.
Why B is correct
NAVEDTRA 14075 §6-5 states that frost and ice buildup insulates the coil and blocks airflow, steadily cutting capacity, which is why freezer coils must be defrosted periodically. Frost does not increase effective heat transfer area.
Cited:NAVEDTRA 14075 §6-5