A split air conditioner has a cabinet with a fan and evaporator for mounting within a structure. The cabinet includes a filter or a stacked filter system positioned in the flow path between an air inlet and an air outlet for filtering contaminants from the air. Movable filters are provided for selectively bypassing the filters to provide a greater or lesser degree of filtration of the air. Preferably, the filters are high performance HEPA-like filter having substantially less pressure drop.