Lennox 18J37 Limit Switch

The Lennox 18J37 Limit Switch is a critical safety component engineered for high-performance thermal regulation in residential and light industrial furnaces. As a normally closed disc-style limit control, this genuine OEM Lennox replacement part is specifically designed to prevent heat exchanger damage by interrupting the burner circuit if internal temperatures exceed safety thresholds. Featuring a yellow color-coded sleeve for rapid field identification, this 175-205F auto limit switch operates with a fixed cut-out temperature of 205°F and automatically resets once the system cools to 175°F. The Lennox 18J37 furnace safety switch ensures precise HVAC high-limit protection and is compatible with a wide range of popular Lennox G23, G26, G32, and 90UGFA series units. Built with a robust stainless steel body for durability in high-cycle environments, this automatic reset limit switch is a direct replacement for legacy part numbers 18J3701 and 60T81, maintaining system integrity and reliable operation for professional contractors.

Key Benefits

• Precise Thermal Calibration: Calibrated for a 205°F cut-out and 175°F cut-in to ensure accurate overheat protection.
• Automatic Reset Functionality: Eliminates manual intervention after a temporary temperature spike, restoring system operation once safe levels are reached.
• Wide Compatibility: Designed for seamless integration with Lennox furnace models, including G23Q, G26Q, and G32V series.
• Industrial-Grade Build: Utilizes a stainless steel housing and NEMA 1 rated construction for longevity in HVACR technical applications.
• Efficient Diagnostics: Part of the 60T81 series terminal configuration, allowing for fast multi-meter testing and installation.

Common Questions

• What causes a Lennox 18J37 to trip frequently? Repetitive tripping usually indicates restricted airflow due to dirty filters, a failing blower motor, or an oversized furnace for the ductwork.
• Can I replace this with a manual reset switch? No. This is an auto reset limit control. Replacing it with a manual version can disrupt the intended safety sequence of the Furnace Control Board.
• How do I verify the 18J37 is faulty? Use a multimeter to check for continuity across the terminals. If the switch is open while at room temperature, the internal disc has failed and requires replacement.

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.