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The Goodman 20162906 M4 Primary Limit Switch is a genuine OEM high-temperature safety control for the Goodman/Amana WFM18070S4BXCB gas furnace. Mounted on the heat exchanger or burner bulkhead, this normally-closed thermal cutout opens the ignition/gas circuit if plenum temperatures exceed a safe threshold — the last line of defense against overheating from a failed blower, dirty filter, or restricted airflow. A limit switch that has tripped permanently or drifted out of calibration causes short-cycling, no-heat lockouts, or nuisance shutdowns.
This genuine Goodman OEM switch is factory-calibrated to the trip temperature and mounting footprint specified for this furnace. Generic limits with the wrong set point or bracket can trip early (constant lockouts) or too late (unsafe overheating). For a life-safety control, OEM is the correct choice.
Easy to Moderate — Power off, disconnect two spade terminals, remove two screws, and swap. Always confirm the underlying cause of any prior trip before returning the furnace to service.