OEM Lennox Blower Speed Relay Kit — 40K58
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The Lennox 40K58 is a genuine OEM indoor blower speed control relay kit (assembly LB-58773DB) that switches the indoor blower motor between heating and cooling speeds. It ensures the fan runs at the correct airflow for each mode, protecting comfort, efficiency, and equipment life in your Lennox air handler or furnace.
Common failure symptoms: When the 40K58 relay fails, you may notice the blower running at the wrong speed, a fan that will not start, weak airflow, a blower stuck on high or low, or chattering and buzzing from the relay contacts. Pitted or welded contacts and a burned-out coil are the usual causes.
Why OEM matters: This kit is matched to the coil voltage, contact rating, and wiring configuration of Lennox blower systems. Installing the genuine OEM 40K58 ensures proper speed switching, prevents motor overload from incorrect ratings, and maintains factory airflow specifications. Generic relays often carry mismatched ratings that lead to premature failure or motor damage, so an exact OEM match is the safe choice.
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