Lennox 19J81 Limit Switch

The Lennox 19J81 is a high-performance HVAC limit switch engineered to maintain critical thermal safety within your furnace plenum. As an OEM furnace high limit switch, it is designed with a specific 210-240F temperature range and a 7-inch insert to provide accurate sensing in the airflow stream. This component functions as a primary safety mechanism, utilizing an auto-reset (L240-30F) SPST configuration that interrupts the heating circuit if the internal temperature exceeds the 240°F threshold, preventing damage to the heat exchanger and potential fire hazards.

For field technicians, the Lennox 19J81 limit control is a direct OEM replacement part for multiple legacy Lennox, Armstrong, and Ducane systems, replacing part numbers 65208800 and 20516702. The 7" probe depth ensures the bi-metal sensor is positioned correctly within the heat exchanger bypass to avoid nuisance tripping while providing rapid response to over-temperature conditions. Its durable construction is built to withstand the high-cycle demands of residential and light commercial forced-air systems.

• Precision Thermal Protection: This 210-240F auto limit switch ensures your furnace shuts down safely before temperatures reach critical levels.
• Broad Compatibility: Serves as a genuine Lennox replacement part for models TUA100SNAF-1, TUA150SNSF-1, and various Armstrong/Concord units.
• Simple Installation: The standardized 7-inch insert and SPST wiring allow for a direct fit in existing furnace safety switch mounting holes.
• Automatic Reset Logic: Features an L240-30F reset profile, meaning the switch automatically closes once the plenum temperature drops 30 degrees below the trip point.

What causes a Lennox limit switch to trip repeatedly?
Frequent tripping usually indicates restricted airflow. Check for a clogged air filter, dirty evaporator coils, or a failing blower motor that isn’t moving enough air across the heat exchanger.

How do I verify if the 19J81 is the correct part for my furnace?
Always check the temperature rating and insert length stamped on your original switch. This model is specifically rated for 240°F actuation with a 7" probe; using an incorrect rating can lead to safety risks or frequent system lockdowns.

Is this a manual or automatic reset switch?
The 19J81 is an auto-reset limit control. If the switch remains open even after the system has cooled, the internal bi-metal disc may be fatigued or damaged, requiring a full 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.