The four main types of HVAC systems are split systems, packaged systems, hybrid systems, and ductless mini-split systems. Split systems are the most common type of HVAC system and consist of an outdoor unit and an indoor unit. The outdoor unit contains the compressor, condenser, and expansion valve, while the indoor unit contains the evaporator coil and air handler. Packaged systems are all-in-one units that contain the compressor, condenser, evaporator coil, and air handler in one unit. Hybrid systems are a combination of split and packaged systems, with the outdoor unit containing the compressor, condenser, and expansion valve, and the indoor unit containing the evaporator coil and air handler. Lastly, ductless mini-split systems are similar to split systems, but they do not require ductwork and are more energy efficient.