White-Rodgers 3L09-18 Limit Switch

The White-Rodgers 3L09-18 is a high-performance 1/2" bimetal disc limit switch engineered for board-mounted applications requiring precise thermal regulation. This fixed temperature control is designed with an open on rise switch action, functioning as a critical safety limit in residential and commercial furnace systems. With a 7.12" insertion length, the sensing element extends deep into the air stream to ensure rapid response times and accurate temperature monitoring. The switch is factory-calibrated to cut out at 155 degrees F and features an automatic reset that restores the circuit once temperatures drop to 125 degrees F. As a veteran-grade HVAC limit control, it replaces worn or pitted snap-disc sensors that cause furnace short cycling or blower motor malfunctions. This SPST normally closed switch is compatible with 24V, 120V, and 240V circuits, making it a versatile OEM replacement part for technicians troubleshooting over-temperature protection failures in modern air handlers.

• Rapid Thermal Response: The bimetal disc technology provides high-speed contact separation to prevent heat exchanger damage.
• Extended Reach: The 7.12" probe length ensures the sensor is positioned correctly within the primary heat zone for reliable limit control.
• Automated Operation: Features an auto-reset mechanism that eliminates manual intervention after the system cools to safe operating levels.
• Broad Compatibility: Rated for low-voltage and line-voltage applications, supporting resistive loads up to 15A at 120VAC.

• What causes a White-Rodgers 3L09-18 to trip? Common causes include restricted airflow from dirty filters, a failing blower motor, or an oversized furnace, all of which drive temperatures above the 155°F limit.
• How do I test this limit switch? Using a multimeter, check for continuity across the terminals at room temperature. Because it is normally closed, a lack of continuity indicates a failed internal contact.
• Can this be used for fan control? No, this model is an open on rise limit switch intended for high-limit safety. For fan-on applications, a close-on-rise switch is required.

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.