The Cleveland Controls NS2-1166-01 Air Proving Switch is an HVAC safety control designed to monitor airflow and verify that adequate air pressure is present during equipment operation. It operates by sensing differential air pressure; when the required pressure level is reached, the internal contacts change state and provide an electrical signal to the control circuit. This switch is ... https://www.partshnc.com/ns2-1166-01-cleveland-controls-air-proving-switch