White-Rodgers 3L09-8 Limit Switch

The White-Rodgers 3L09-8 Limit Switch is a high-performance 1/2" bimetal disc limit control designed for precise temperature regulation in forced-air furnaces and industrial process equipment. Featuring a 3.12" insertion length, this board-mounted switch utilizes an open on rise action, triggering at a fixed open temperature of 180°F to prevent overheating. It is engineered with an auto reset mechanism that restores continuity once the ambient temperature drops to the fixed close temperature of 140°F. This Therm-O-Disc Type 36T style control ensures high-speed contact separation for long-term reliability in demanding HVAC cycles. For technicians performing field service, the White-Rodgers 3L09-8 offers a drop-in solution for board-mount applications requiring specific thermal profiles. Its compact bimetal design provides accurate sensing and rapid response times, making it a critical safety component for maintaining system integrity within heating controls and commercial ventilation units.

• Precise Thermal Safety: Fixed 180°F cutout protects heat exchangers and critical components from excessive temperature spikes.
• Automatic System Recovery: Integrated 140°F reset differential ensures the system returns to operation without manual intervention after cooling.
• Simplified Board Mounting: Designed with a 3.12-inch probe and 1/2-inch disc for seamless integration into existing control boards.
• OEM-Grade Reliability: Features high-speed contact separation to minimize arcing and ensure a longer service life in high-cycle environments.

What is the difference between open on rise and close on rise for this switch?
The White-Rodgers 3L09-8 is an open on rise switch, meaning it breaks the electrical circuit when the temperature hits 180°F to stop the heating process for safety. A close on rise switch would do the opposite, typically used for fan control.

Can this limit control be used in multi-stage furnaces?
Yes, as long as the 180°F setpoint and 3.12-inch insertion length match the original manufacturer’s specifications for the specific furnace board-mount slot.

Does the orientation of the 1/2" bimetal disc matter during installation?
The disc must be positioned so that the airflow or heat source directly impacts the sensing element. Proper insertion depth of 3.12 inches is required to ensure the switch accurately reads the internal plenum temperature.

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.