Armstrong Furnace R604221 01 Switch This DSI electrode Amana Goodman part This DSI electrode Amana Goodman part features a robust ceramic insulator and precision gapped probe for consistent performance under varying gas pressures and combustion airflows Smith BTP and Cyclone series units where flange gasket replacement is required to maintain peak hydraulic efficiency and prevent oxidative corrosion at the joint The Armstrong Furnace R604221 01 Door Switch is a critical safety interlock component designed for modern HVAC systems This interlock switch must be fully functional to ensure the safety of the homeowner and the equipment