The most common type of central air conditioning is the split system which features a condenser outside the home and fan-and-coil system inside connected by pipes carrying refrigerant. However, not every home can accommodate the ductwork needed to install central air. For such residences, a split ductless system is an option.
Central air conditioning
Central air-conditioning systems use ducts to distribute cooled air throughout the house. In a "split system," the typical design, refrigerant circulates between an indoor coil and a matching outdoor condenser with compressor. The refrigerant cools the air, dehumidifying it in the process; a blower circulates air through ducts throughout the house. A variation is the "heat pump," a type of system that functions as heater and cooler. When used as an air conditioner, a heat pump discharges heat from the house either into the air or deep into the ground. In the winter, a heat pump extracts heat from the ground or the air to warm the house.
Split ductless systems
Split ductless systems are similar to central air. They have an outside condenser and one to four indoor units with blowers mounted high on the wall. Tubing connects the parts and circulates refrigerant. The tubing, along with an electric and drain line, is run through a 3-inch hole hidden behind the indoor unit. Each indoor unit cools the room it's installed in and has its own remote control. Unlike central systems, split ductless systems need no ductwork, making them easier to add to homes without existing ducts. Split ductless systems are more expensive than window air conditioners, and professional installation is recommended, but it's a way to add cooling without tearing up walls to install ducts.
Some systems use pipes instead of ducts, which distribute chilled water to heat exchangers in more than one room.