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The Goodman B1370189 is a genuine OEM primary high-limit switch rated to open at 200°F, built for the Goodman GMNT090-5B gas furnace and compatible GMNT-series units. Mounted on the heat-exchanger bulkhead, the primary limit is the furnace's main overheat protector: if supply-air temperature exceeds the setpoint due to restricted airflow or blower failure, it opens the gas-valve circuit to prevent heat-exchanger damage.
The primary limit is a core safety device, so an exact 200°F setpoint and correct mounting depth are essential. This OEM switch matches Goodman's factory specification. Generic switches may vary in trip temperature or terminal orientation, which can cause short-cycling or missed protection. OEM is strongly recommended.
Easy — Power off, disconnect the two leads, and secure the replacement in the original bracket. If the limit was tripping, correct any airflow restriction (filter, coil, ductwork, blower) before returning the unit to service. Professional diagnosis recommended for repeat trips.