A split-system air conditioner separates the hot and cold side of the system. The cold side, consisting of the expansion valve and the cold coil is generally placed into a furnace or some other air handler. The air handler blows air through the coil and routes the air throughout the building using a series of ducts. The hot side of the split air system is known as the condensing unit, which lives outside the building. This split approach has evolved over the years because it’s cost efficient and results in reduced noise inside the house, but at the expense of increased noise outside the house.