2026-10-22 A Constant Air Volume (CAV) controller is a device installed in an air duct that holds the airflow passing through it at a fixed, pre-set value — regardless of how the pressure inside the duct changes. It can be thought of as a "cruise control" for air: just as cruise control keeps a car at a steady speed on hills and valleys, a CAV controller keeps the air volume steady even when the fan speeds up, dampers elsewhere open or close, or filters gradually clog