An RAC air conditioner is a rectangular or square unit which is attached through a wall or in a window and only cools and/or heats a single room. The air is distributed through a vent on the front of the unit.

Central Air Conditioning | Department of Energy
A central air conditioner is either a split-system unit or a packaged unit. In a split-system central air conditioner, an outdoor cabinet contains the outdoor heat exchanger, fan, and compressor, and an indoor cabinet contains the indoor heat exchanger and blower.