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

The purpose of a defrost cycle in a heat pump is to remove frost buildup from the outdoor coil during heating mode. In cold weather conditions, moisture in the air can freeze on the surface of the outdoor coil, which is critical for heat absorption. When the outdoor coil becomes overlaid with frost or ice, it restricts airflow, reducing the heat pump's efficiency and heating capacity.

During the defrost cycle, the heat pump temporarily reverses its operation, allowing warm refrigerant from the indoor coil to flow to the outdoor coil. This process melts the accumulated frost or ice, ensuring that the heat pump can effectively extract heat from the outside air again. By maintaining a clear coil surface, the system can operate efficiently and deliver the necessary heating to the indoor environment.

Other options, though they may relate to different functionalities, do not address the primary reason for the defrost cycle, which is specifically aimed at managing frost and ensuring optimal heat pump performance in colder temperatures.