What is the primary purpose of the defrost cycle in a heat pump?

• A. Prevent ice buildup on the outdoor coil
• B. Increase indoor air temperature
• C. Improve humidity control
• D. Reduce refrigerant pressure

Answer: (A)

The main idea is that the defrost cycle keeps the outdoor heat exchanger from getting blocked by ice, which would slam the brakes on heat transfer. When a heat pump operates in heating mode in cold, humid conditions, moisture from the air can freeze on the outdoor coil. That ice acts like an insulator and greatly reduces the system’s ability to pull heat from outside. The defrost cycle temporarily reverses refrigerant flow so the outdoor coil becomes the condenser and is heated, melting the ice. Once the frost is cleared, the unit returns to normal heating. This keeps performance and efficiency from dropping in cold weather. It’s not about making indoor air hotter, nor about humidity control, nor about lowering refrigerant pressure—the purpose is specifically to prevent ice buildup on the outdoor coil.