OEM Lennox Limit Switch — 38M66
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The genuine OEM Lennox 38M66 limit switch is a high-temperature safety control that guards your Lennox furnace against overheating. Installed near the heat exchanger, it continuously senses plenum temperature and breaks the burner circuit if the furnace climbs past its safe operating limit — commonly caused by reduced airflow from a dirty filter, a failing blower motor, or obstructed ductwork.
Common failure symptoms: The furnace short-cycles on a heat call, burners fire and then shut down after a few minutes, the unit produces no heat, or the blower fails to shut off. A 38M66 that fails open locks the furnace out of heating mode, while one that fails closed no longer protects the heat exchanger from heat-induced cracking.
Why OEM matters: The Lennox 38M66 is calibrated to the precise trip and reset temperatures specified for your furnace. Aftermarket switches with the wrong ratings can allow unsafe overheating or cause repeated nuisance trips. The factory-spec part guarantees accurate calibration, correct terminal and mounting fit, and the dependable protection your Lennox equipment was designed to have.
Shipping Information
- Orders placed before 3PM CST ship same business day
- Standard delivery: 2-5 business days
- Express shipping available at checkout
- Free shipping on orders over $75
- Tracking number emailed upon shipment
Return Policy
- 30-day returns on unused parts in original packaging
- Electrical parts (capacitors, contactors, control boards) are final sale once installed
- Email info@nationalhvacparts.com to initiate a return
- Refunds processed within 5-7 business days