The defrost cycle is a temporary reversal of the refrigeration process used by heat pumps to melt ice that has formed on the outdoor coils. During the winter, moisture in the air can freeze on the Heat Pump Condenser, which blocks airflow and reduces heating efficiency. When the system detects ice, it switches to cooling mode for a few minutes to heat up the outdoor coil while turning on the Electric Heat Strip indoors to keep the home warm. This process is fully automated in ACIq and MrCool systems to ensure uninterrupted comfort. If your system stays frozen for long periods, it may indicate a failure in the defrost control board or a low refrigerant charge. You can find replacement defrost sensors and boards in our Parts collection to fix these issues. Proper drainage is necessary during this cycle to prevent the melted water from refreezing into a block of ice at the base. It is a vital function for any heat pump operating in climates that experience freezing temperatures.