The defrost cycle of a heat pump is its way of trying to operate efficiently during cooler months. A defrost control tells the reversing valve when to send hot refrigerant outdoors to thaw the outdoor coil during the winter. During the defrost cycle, your auxiliary heat takes over, which reduces the heat pump's overall efficiency by up to 10 percent. The two most common types of defrost controls are time-temperature and demand-defrost.… Read more