Defrost
Short definitionMelting the frost that builds up on the evaporator, at set intervals.
Moisture entering the room turns to frost on the cold surface of the evaporator. As the frost thickens, air cannot pass and cooling drops off. So several times a day the unit is heated for a short time to melt the frost.
In rooms above 0 °C, running the fan is usually enough. Below 0 °C, electric heaters or hot gas are used. The heat put into the room during defrost is part of the heat load too.