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The Goodman B1370188 Primary Limit Switch is the genuine OEM 170°F auto-reset high-limit control for the AMS80904BNAA gas furnace and compatible Goodman/Amana models. Mounted on the heat exchanger's supply-air side, this is the furnace's main overheat safety: if supply temperatures climb past 170°F due to restricted airflow, it cuts the burner circuit while keeping the blower running to purge excess heat, protecting the heat exchanger from cracking.
The OEM Goodman B1370188 is calibrated to the exact 170°F set point and disc geometry the furnace requires. Because the primary limit is the last line of defense for the heat exchanger, a generic switch with drifted calibration or a mismatched insertion depth is a real safety risk. Install OEM only.
Difficulty: Easy. Remove two spade wires and the mounting screws, then insert the new limit at the same depth — about 15 minutes. Always disconnect power and gas first. If the limit was tripping, correct the airflow restriction (filter, ducting, blower) before returning the unit to service.