Lennox 87H91 Limit Switch

The Lennox 87H91 Limit Switch is a critical safety component designed for precise thermal regulation within the heating vestibule. This OEM Lennox furnace part functions as a normally closed SPST (Single Pole Single Throw) switch, engineered to break the electrical circuit and shut down the burner if internal temperatures exceed safety parameters. Specifically rated for a 130-170F temperature range, it features an automatic reset mechanism that restores operation once the heat exchanger cools to 130°F. As a veteran-grade replacement, the 87H91 is a direct match for legacy part numbers 87H9101, 42256, 52M43, and R20001103, ensuring seamless integration for contractors servicing Lennox, Armstrong, and Ducane units.

Built with a 1.5-inch to 1.75-inch insertion length, this high-limit control switch is essential for preventing cracked heat exchangers and ensuring the blower fan cycles at the correct thermal thresholds. Whether you are troubleshooting a furnace short cycling issue or addressing a blower fan running constantly, verifying the limit's cut-out point is the first step in a professional diagnostic. This genuine Lennox replacement part maintains the factory-specified safety sequence of your HVAC equipment, providing the reliability required for high-duty residential heating applications without the risk of improper calibration found in universal alternatives.

• Universal Compatibility: Exact drop-in replacement for part numbers 87H9101, 42256, 52M43, and L170-40F.
• Automatic Reset Logic: Eliminates the need for manual intervention by resetting the circuit once temperatures drop to 130°F.
• Precise Thermal Protection: Opens at 170°F to prevent overheating, protecting the furnace cabinet and heat exchanger.
• Durable OEM Construction: Designed specifically for Lennox-brand air handlers and furnaces to ensure long-term mechanical cycling.

What are the signs of a failing Lennox 87H91 limit switch?
Common indicators include the furnace shutting down before reaching the thermostat setpoint (short-cycling) or the blower fan continuing to run even after the burners have extinguished, as the switch may be stuck in the open or closed position.

Can I use this to replace a manual reset limit switch?
No. In professional applications, you should never swap an auto-reset limit for a manual reset safety. Manual reset switches are typically used for flame rollout and require a physical inspection of the system before restarting.

Does insertion length matter during installation?
Yes. This part features an approximate 1-1/2" to 1-3/4" insert. Using a switch with the wrong depth can lead to inaccurate temperature readings, causing the unit to trip prematurely or fail to detect an actual overheat condition.

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.