Lennox 18K69 Limit Switch

The Lennox 18K69 Limit Switch is a critical safety component designed for precise thermal management in Lennox electric furnaces and air handlers. This OEM replacement part, also identified as 18K6901, features an L150F L333F configuration, meaning it is set to "Open on Rise" when temperatures hit the 150°F threshold and automatically resets when the system cools to 110°F. For a technician in the field, this auto-reset limit switch ensures the heating elements are deactivated before thermal runaway can damage the heat exchanger or internal wiring. The Lennox 18K69 is a normally closed disc-style switch engineered for high-cycle reliability in residential and commercial HVAC replacement applications. Whether you are troubleshooting a furnace that starts then stops or addressing a complete loss of heat, verifying continuity on this primary limit control is a standard diagnostic step. This genuine part is directly compatible with a wide range of Allied, Armstrong, and Ducane equipment, maintaining original factory safety specifications.

• OEM Compatibility: Direct replacement for part numbers 18K69 and 18K6901, ensuring exact fitment in Lennox-branded air handlers.
• Precise Thermal Calibration: Factory-set to actuate at 150°F (L150) with a fixed 40-degree differential for a 110°F reset.
• Automatic Reset: Eliminates the need for manual intervention once the plenum temperature returns to a safe operating range.
• Durable Disc Construction: Built to withstand the constant thermal cycling found in high-efficiency electric heating stages.

What is the difference between 18K69 and 18K6901?
These parts are functionally identical. The 18K6901 is simply the updated catalog number for the original 18K69 switch.

How do I test if my Lennox limit switch is bad?
Using a multimeter, check for continuity across the terminals when the switch is cool. Since this is a normally closed switch, a lack of continuity at room temperature indicates a failed component that requires replacement.

Will this work for gas furnaces as a rollout switch?
No, this is specifically an electric heat limit switch. Rollout switches typically require a manual reset for safety, whereas the 18K69 utilizes an automatic reset for air handler high-limit protection.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.