The normal method is a hot gas defrost. Basically the refrigerant flow is changed so hot liquid refrigerant flows to the condenser instead of cold liquid, this then defrosts the condenser in 'super quick time'. Normally it is a fixed time defrost that is run when a designated temperature is reached or exceeded for a set period of time.
The split type a/c units turn off the interior fan while defrost is active so the user doesn't suddenly get a blast of cold air.
On my own controller I monitor the temperature of the condenser so can cut short the defrost cycle if necessary.
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