The externally equalized configuration ensures maximum evaporator efficiency by compensating for pressure drops

as newer OEM HVAC control boards may feature updated footprints to accommodate advanced circuitry

System Protection: Acts as a primary safety interlock to prevent the heater from operating under low-flow or no-flow conditions

and potential moisture carryover into downstream sensitive pneumatic instrumentation

including the 1/2"

McDonnell & Miller 150S-M-HD Controller Refrigerant The externally equalized configuration ensuresThe McDonnell & Miller 150S M HD Controller (Part Number 173203) is a heavy duty, replacement head mechanism designed for industrial and commercial steam boiler applications. This combination low water cut off and pump controller features a snap acting manual reset switch, providing essential safety redundancy by preventing the burner from firing if a low water condition occurs. Engineered for durability, the unit utilizes a corrosion resistant Monel