Refrigeration Cycle: Compressor → Condenser → Expansion → Evaporator Types: Vapor compression, vapor absorption, gas refrigeration Air Conditioning: Controls temperature, humidity, air quality Psychrometrics: Air properties – dry bulb, wet bulb, RH, enthalpy Components: Compressor, condenser, evaporator, expansion device, ducts, fans Applications: Domestic, commercial, industrial HVAC systems