Abstract: A conditioning apparatus for racks for electrical, electronic and telecommunications instruments and the like, comprising at least one cabinet with inside a rack chassis for instruments, air passage gaps being formed between the door of the cabinet and the rack chassis and between the cabinet back and the rack chassis. The cabinet is open in an upper region onto a first air conveyance element and in a lower region onto a second air conveyance element that are connected respectively to at least one third and one fourth conveyance elements arranged above and below at least one associated air-conditioning module. At least one first, second and third shutters are adapted to allow, modulate or inhibit the air circulation for conditioning of the free cooling type.