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The Goodman 20162906 M4 Primary Limit Switch is the genuine OEM high-limit safety control for the AMEC800403ANAA gas furnace and compatible Goodman/Amana models. Mounted on the heat exchanger or plenum, this thermal switch monitors supply-air temperature and shuts off the burners if the furnace overheats — protecting the heat exchanger and preventing a fire hazard. A failed limit switch is a common cause of a furnace that short-cycles, locks out, or won't fire at all.
This genuine OEM Goodman switch is calibrated to the exact trip temperature your furnace's control board expects. Generic substitutes may open at the wrong temperature, causing nuisance lockouts or, worse, failing to trip. For a safety component, OEM is the recommended choice.
Easy to Moderate — remove two mounting screws and transfer the wiring. Disconnect power at the breaker before servicing and verify orientation against the old switch. Replacement typically takes under 20 minutes.