OEM Lennox Fan/Limit Thermostat 135-175°F — 21P84
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The genuine OEM Lennox 21P84 is an adjustable fan and limit thermostat with a 135–175°F operating range and a 40°F differential. This dual-function control energizes the blower once the heat exchanger reaches temperature and acts as a high-limit safety switch, shutting off the burner if the furnace overheats. It protects your Lennox equipment while ensuring the fan only runs when there is usable heat to deliver.
When a fan/limit switch fails, you may experience a blower that runs constantly or never starts, short cycling on the high limit, cold air blowing at startup, or a furnace that shuts down on an overheat safety. A worn bimetal element or pitted contacts are common causes of these symptoms.
Choosing the OEM Lennox 21P84 guarantees the correct temperature range, differential, and mounting for Lennox furnaces. Because this is a safety-critical control, an incorrect or generic substitute can allow unsafe operation or nuisance shutdowns. The factory part delivers the precise calibration and reliable protection your Lennox system was engineered for.
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