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The Goodman 20162906 is a genuine OEM M4 primary limit switch (high-limit control) for the WFM18070S3AXCC gas furnace. Mounted on the heat-exchanger bulkhead, this auto-reset thermal switch continuously monitors supply-air temperature and opens the control circuit to shut off the burners if the furnace overheats — typically from restricted airflow, a failed blower, or a clogged filter. Once temperatures return to normal, an auto-reset primary limit closes again and allows normal operation to resume. A failed-open or drifting switch causes short-cycling or a no-heat condition.
The M4 primary limit is calibrated to a precise trip temperature and mounting depth matched to this heat exchanger. A generic switch with a different setpoint or probe length can nuisance-trip or fail to protect the unit. For a primary combustion safety control, always fit the OEM-specced part.
Moderate — Remove two mounting screws and transfer the two spade connectors, roughly 15–25 minutes. Shut off gas and power first, note wire positions, and make sure the sensing element seats correctly in the airstream. If overheating persists after replacement, diagnose airflow before returning the furnace to service.