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Defrost
Defrost is the automatic mode in which a heat pump briefly removes frost from the outdoor unit’s heat exchanger.
When it is around 0 °C and humid outside, the outdoor unit’s heat exchanger runs colder than the air around it, so frost builds up on it. Frost reduces heat transfer, so the heat pump automatically starts a defrost cycle: for a few minutes heat is directed to the outdoor coil, the ice melts and the water drains away.
- Defrost is a normal part of operation, not a fault – you may see steam rising from the unit.
- How often it runs depends on humidity, temperature and the controller logic; it is most frequent on damp shoulder-season days.
- The meltwater must drain freely: the unit is mounted on brackets or a base above snow level so that no ice mound forms beneath it.
Modern Mitsubishi Electric units control defrost according to actual conditions, keeping the interruption of heat to the rooms as short as possible. In water-based systems, sufficient system volume or a buffer tank helps bridge this period. When choosing the outdoor unit location, our specialists assess drainage, prevailing winds and snow drifts – these directly affect reliable winter operation.