Debris is filtered from refrigerant in a refrigerant system by: (1) installing a filtration apparatus in the high pressure side of a refrigerant system, the apparatus comprising a filtration housing having primary and secondary passages, a primary filter disposed in the primary passage, and a diverter means for selectively directing refrigerant flow through either the primary or the secondary circuit passages; (2) directing refrigerant flow through the primary circuit passage; (3) operating the refrigerant system until a shifting parameter is obtained; and (4) operating the diverter means so as to direct refrigerant flow to the secondary circuit passage. Optionally, a secondary filter is disposed in the secondary filter channel. In alternate methods, the shifting parameter comprises one of: elapsed time of operation of the system; selected differential pressure across the primary filter; or a selected compressor discharge pressure above said normal compressor discharge pressure.