Refrigeration is the process of removing heat. Air- conditioning is a form of air treatment whereby temperature, humidity, ventilation, and air cleanliness are all controlled within limits determined by the requirements of the air conditioned enclosure. The basic simple vapour refrigeration system is discussed and the significance of using the p-h plots for the cycle is emphasized. The simple refrigeration cycle is made up of four fundamental processes.Compression, Condensation, Expansion and Vaporisation. Major Components of the Vapour Compression System are Compressor: compresses and 'circulates' refrigerant vapour, Condenser: rejects heat to the atmosphere (a heat exchanger), Liquid Receiver: a vessel designed to store liquid refrigerant, RMD (Refrigerant Metering Device): regulates flow of refrigerant into the evaporator. and Evaporator: absorbs heat from the medium being cooled (a heat exchanger).Instead of compressor, the Vapour Absorption Cycle consists of Generator, Absorber and Pump. Air conditioning is the automatic control of Temperature, Relative Humidity, Air Cleanliness, Air Distribution, Noise and Purity.