A split air conditioner system is one in which the evaporator coils and air handler are physically separated from the condenser coils. These are also known as central air-conditioning systems, since the separated evaporator and air handler are often placed in a central location to cool the entire building.
An air conditioner is essentially a heat pump that uses a coolant liquid to transfer heat from the indoor air to the outdoor atmosphere. Coolant flows through the indoor evaporator coils, absorbing heat from the air and expanding it into a gas. This gas is compressed and pumped outside, where it passes through the condenser coils and expels heat, condensing back into a liquid state. Each pass the coolant makes through the system transfers more heat outdoors.
In a window air conditioner, the evaporator coils and condenser coils are combined into a single unit, transferring heat from the indoor half of the device to the exhaust system hanging outside the window. A split system physically separates these two halves, allowing the installer to place the evaporator and air handler anywhere in the home, with the condenser unit connected only by the coolant pipes. This is especially beneficial in multifamily units or commercial buildings, where multiple condensers can be situated on the roof of a building to keep them out of sight.