If the vacuum is correct but the SPST switch shows an open circuit with a multimeter

While primarily used in commercial air handlers and rooftop units

the 1186788 is the direct manufacturer-recommended superseding part for the 1171780 rectifier board

along with HC Series HumidiClean models

this upgraded model integrates seamlessly into existing setups

Armstrong Fluid Technology 816305-058 Impeller 320819-301 If the vacuum is correctThe Armstrong Fluid Technology 816305 058 Impeller is a precision engineered 3. 875" bronze impeller designed for high performance fluid circulation in commercial and industrial HVACR systems. As a critical component for the Armstrong S 45 circulator pump, this centrifugal pump impeller is manufactured from high quality bronze to provide exceptional corrosion resistance and structural integrity, specifically in potable water or open loop systems where