A room air conditioner mounted on an external building wall (27), the room air conditioner including: (a) an indoor unit (21) including: (i) an indoor cabinet; (ii) an indoor heat exchanger (71) mounted in the indoor cabinet; (iii) an indoor fan (73) mounted in the indoor cabinet; and (iv) means for humidifying the indoor air (76), disposed in the indoor cabinet; (b) an outdoor unit including: (i) an outdoor cabinet; (ii) an outdoor heat exchanger (84) mounted in the outdoor cabinet; (iii) an outdoor fan mounted in the outdoor cabinet; (iv) a fan motor mounted in the outdoor cabinet; and (v) a pump (83) connected to a condensate transfer tube; and (c) an interface unit (24) mounted within an opening in the external building wall, the interface unit for communicating between the indoor unit and the outdoor unit, wherein the condensate is conveyed by the pump to the means for humidifying the indoor air via the interface unit.