The furnace pressure switch , Armstrong Furnace R100684-04 Pressure Switch, available at PartsHnC, is a crucial component designed to ensure safe and efficient furnace operation. Operating at .65 inches WC (water column) and featuring SPST (single pole, single throw) functionality, this switch monitors pressure levels within the furnace. https://www.partshnc.com/r100684-04-armstrong-furnace-65-wc-spst-pressure-switch