Ice on heat pump

Ice on a heat pump is completely normal. In operation the heatpump removes heat from outside air and delivers this heat into the home. When the temperature falls below about 45F and the humidity is high enough the moisture condenses on the heat pump fins. The heat pumps have sensors to detect the ice buildup and will reverse every 40 to 90 minutes to defrost the external coils and restore the ability to move air through the fins. If the system runs, builds up ice and does not periodically defrost itself the system is in need of service as the defrost cycle is not being initiated properly.