During normal operation over winter months, heat pumps routinely perform a defrost cycle to clear ice build up on the condenser coil.
In heating mode a heat pump extracts heat from the outside air. This heat is transferred into warm air circulating throughout your home. When the ambient temperature outside is close to or below 0°C, moisture in the air freezes on the outdoor unit condenser coil. When the system recognizes ice forming on the outdoor coil, a defrost cycle is triggered, removing ice and ensuring the system transfers heat most efficiently.
Any ice building up on the outside heat exchanger reduces the airflow across it, which will effect the efficiency, sometimes reducing it dramatically. In extreme cases this can also cause damage to the outdoor unit.
In heavy snow fall, it is recommended to shut unit to avoid snow from accumulating in and out. When the storm is completed, clear the snow around the unit. If snow has accumulated in unit, shut the breaker and use warm water to clear pan area of snow and ice.
Failure to clear the unit of snow and ice will jeopardize the warranty.