An air conditioning unit having: a first air passageway and a second air passageway adjacent to the first air passageway. Dampered air inlets are provided at one end of the first and second air passageways to selectively provide indoor air or outdoor air to each passageway. There is an indoor air outlet in the first air passageway and an outdoor air outlet in the second air passageway, both outlets at the other end of the passageways. There is a first blower in the first passageway and a second blower in the second passageway for moving air through each passageway. The unit has a refrigerant system with an evaporator in the first passageway, a compressor, a condenser in the second passageway, and a refrigerant line joining the evaporator, the compressor, and the condenser, in series, in a closed loop. The unit can be used in an air conditioning mode, a dehumidifying mode and a purge / ventilating mode. The unit is particularly suited for use in an indoor swimming pool.