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The Goodman 20162906 M4 primary limit switch is the high-temperature safety control for the GMH951155DXAB gas furnace. Mounted on the heat-exchanger housing, it opens the circuit and shuts off the burners if plenum temperature exceeds a safe threshold — protecting against a failed blower, dirty filter, or restricted airflow. A failed limit switch causes short cycling, no-heat calls, or blower lockouts.
The OEM 20162906 is calibrated to the exact trip and reset temperatures Goodman specs for this heat exchanger, ensuring the furnace is protected without nuisance trips. Generic limits with different set points can either fail to protect the unit or cause premature shutdowns. This is a safety component — OEM is strongly recommended.
Cut power at the disconnect, unplug the two wire leads, remove the mounting screws, and install the new switch in the same orientation. Confirm continuity and correct seating before restoring power.