Lennox 18K43 Limit Switch

The Lennox 18K43 Limit Switch is a high-temperature safety control engineered for precision in Lennox furnaces and heat pumps. This Normally Closed (NC) switch is designed to interrupt the ignition circuit upon detecting excessive temperatures, effectively protecting the heat exchanger from thermal stress. As a genuine Lennox OEM replacement part (also identified as Lennox 18K4301), it provides exact mechanical and electrical compatibility for a seamless drop-in installation. With an automatic reset function, the switch opens at a high-limit threshold of 300°F and closes once the internal temperature drops back to 270°F, ensuring continuous monitoring without manual intervention. The 7-inch insertion length allows for accurate temperature sensing within the primary airflow of the furnace. This high-limit switch is critical for maintaining system safety and preventing hazardous rollout conditions in supported Allied, Armstrong, and Ducane equipment.

• OEM Precision: Guaranteed compatibility with Lennox GHR26 and GHR32 series furnaces, ensuring peak performance.
• Automatic Reset: Eliminates the need for manual resets by automatically closing at 270°F after a thermal trip.
• High-Temperature Protection: Reliable 300°F cut-out threshold prevents critical component damage during overheating.
• Durable Construction: Built to withstand high-cycle thermal environments common in industrial and residential HVACR applications.
• Verified Specifications: Red color-coded for quick identification as a 300-degree fixed limit control.

What causes a Lennox 18K43 limit switch to trip?
A trip is usually triggered by restricted airflow, such as a clogged filter, a failing blower motor, or obstructed ductwork, causing the internal temperature to exceed the 300°F limit.

How do I test if the 18K43 limit switch is defective?
Using a multimeter, check for continuity across the terminals when the switch is cool. If the switch remains open (no continuity) at room temperature, it needs to be replaced.

Can I use a 18K4301 as a direct replacement for the 18K43?
Yes, the 18K4301 is the updated manufacturer part number and is functionally identical in temperature rating and insertion depth.

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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.