This document provides information on HVAC (heating, ventilation, and air conditioning) systems. It discusses the history and basics of air conditioning, including the five parameters controlled by AC units. The key components of AC systems, including the evaporator, condenser, compressor, fan, and expansion valve, are described. Different types of HVAC systems are classified and explained, such as central AC, heat pumps, VRF systems, chilled water systems, window units, split units, and types of split units. Factors to consider for HVAC system design are also listed.