OEM Lennox Limit Switch — 79J89
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The genuine OEM Lennox 79J89 limit switch is a temperature-sensing safety control that monitors heat in your furnace's heat exchanger and plenum. If temperatures climb above a safe threshold — usually from restricted airflow — the switch opens and shuts off the gas burners to prevent overheating and heat-exchanger damage.
Common failure symptoms: the furnace short-cycles on high heat, the blower runs constantly, no heat with a limit or lockout fault code, or burners that light and quickly cut out. A switch that has drifted out of calibration or failed open will stop the furnace even when conditions are normal, while a dirty filter or blocked duct can also trip a healthy switch.
Why OEM matters: the 79J89 is calibrated to the precise trip and reset temperatures your specific Lennox furnace requires and mounts to match its exact location. A mismatched aftermarket limit can trip too early, too late, or fail to protect the heat exchanger at all. Installing the factory OEM switch restores correct safety operation and reliable heating for your Lennox system.
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