York S1-024-35272-000 is an SPNO close-on-fall pressure switch set at –0.54 inches water column, designed to ensure safe airflow and draft control in HVAC systems. The switch functions by sensing pressure changes and closing the normally open contacts when pressure falls to the specified level, confirming proper venting conditions. It is commonly used in York gas furnaces, rooftop uni... https://www.partshnc.com/54wc-spno-close-on-fall-sw