Abstract: A room air conditioner for mounting in a window opening having a vertically sliding lower sash. The enclosure for the unit has front and rear portions separated by the vertical plane of the window opening, the compressor and condenser heat exchanger being mounted in the rear portion, and the evaporator heat exchanger being mounted in the front portion. A motor that is connected to an axial flow fan at one end and a coaxial centrifugal blower wheel at the other end is also located in the rear portion. The axial flow fan is operatively associated with the condenser heat exchanger and the centrifugal blower wheel is operatively associated with the evaporator heat exchanger. The forward enclosure portion and the evaporator heat exchanger extend above the bottom of the bottom rail of the lower sash, and the rear housing portion and the condenser heat exchanger extend above the bottom rail of the lower sash and substantially below the level of the window sill.