An air distribution system in HVAC typically consists of a blower or fan, air handling unit (AHU), ductwork, vents, and diffusers. The blower or fan draws in air, which is then filtered, cooled or heated, and humidified or dehumidified in the AHU. The conditioned air is then distributed through the ductwork to the vents and diffusers, which direct the air into the occupied spaces. Proper design, installation, and balancing of these components are crucial for efficient and effective air distribution.