What is the defrost cycle used to prevent in a heat pump's outdoor coil?

• A. Ice buildup on outdoor coil
• B. Compressor overload
• C. Refrigerant leakage
• D. Humidity increase

Answer: (A)

Ice buildup on the outdoor coil is the problem the defrost cycle addresses. When a heat pump runs in cold weather, moisture in the air can freeze on the outdoor coil, creating frost that insulates the coil and blocks airflow. That reduces heat transfer, lowers efficiency, and can increase compressor stress. The defrost cycle reverses the refrigeration flow for a short time so the outdoor coil is heated (by hot refrigerant gas or indoor heat) and the ice melts. After the ice clears and the coil warms, the system returns to heating. Defrost is typically triggered by coil temperature, pressure, or a timer.