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The Goodman B1370189 Primary Limit Switch is a genuine OEM high-limit safety control for the AMH80905CNAB gas furnace. Positioned over the heat exchanger, the primary limit is the furnace's main overheat protection: it opens the gas-valve circuit whenever supply-air temperature climbs past the safe threshold — usually caused by a dirty filter, closed dampers, or a failing blower — and closes again once temperatures return to normal.
Our OEM Goodman B1370189 arrives calibrated to the certified 200°F trip point with the correct probe length and bracket for the AMH80905CNAB. Universal aftermarket limits may use a different setpoint or probe depth, which can cause short-cycling on the gas valve or, if rated too high, allow the heat exchanger to overheat. For the furnace's primary safety, OEM is the right choice.
Easy (2/5). Kill power, remove the two spade terminals and the mounting screws, and drop in the new limit at the same depth. About 15 minutes. Frequent tripping almost always points to an airflow problem — replace the filter and confirm blower operation before returning the unit to service.