Thermostatic Vacuum Switch
Remove switch and connect suitable lengths of tubing to fittings "C" and "D". Blow down tube "D", air should be emitted from tube "C", if not replace switch. Immerse switch bulb in oil bath and heat oil to 220°F. Blow down tube "D", air should be emitted from fittings "Fl" and "MT", if not, or if air is emitted from "C", replace switch. Be sure to clean oil from switch before reinstalling.