White-Rodgers 3L09-28 Limit Switch

For service technicians requiring a precise thermal safety solution, the White-Rodgers 3L09-28 Limit Switch delivers industrial-grade performance in a compact 1/2" bimetal disc package. This board mounted limit control is specifically engineered with a 3.12" insertion length to monitor internal plenum temperatures effectively. The switch features a fixed open temperature of 210 degrees F and a fixed close temperature of 180 degrees F, providing a consistent 30-degree differential essential for furnace safety circuits. Utilizing an open on rise switch action and an auto reset mechanism, the 3L09-28 ensures that the system safely cycles down during high-limit excursions and restores continuity once temperatures return to the 180°F threshold. This HVAC high limit thermostat is a standard replacement part used across numerous OEM platforms, offering the high-speed contact separation required for reliable inductive load switching in residential and light commercial heating equipment.

Key Benefits for Technicians:

• Precise 210°F Setpoint: Fixed temperature calibration prevents drifting, ensuring the White-Rodgers 3L09-28 trips exactly when thermal limits are reached.
• Optimized Insertion Depth: The 3.12-inch probe length allows the bimetal disc to sit squarely in the airflow path for faster response times.
• Automatic Reset Logic: Eliminates unnecessary service calls by resetting the circuit automatically at 180 degrees F once the heat exchanger cools.
• Versatile Board Mounting: The 1/2 inch bimetal disc design is compatible with standard furnace control boards and mounting brackets for rapid installation.

Common Questions:

What is the difference between an auto-reset and a manual reset limit switch?
An auto-reset switch like the 3L09-28 will automatically close the circuit once the temperature drops below the fixed 180°F reset point, whereas manual reset models require a technician to physically depress a button to restore operation after a trip.

Can I use a 3.12" insertion switch in place of a shorter probe?
It is critical to match the 3.12" insertion length specified by the OEM. A probe that is too long may interfere with internal components, while one that is too short may sit in a "dead air" pocket, leading to delayed tripping and potential safety hazards.

How do I verify if my White-Rodgers limit switch has failed?
Using a multimeter, check for continuity across the terminals. Since this is an open on rise switch, you should see 0 ohms (closed) at room temperature. If the circuit is open while the furnace is cool, the bimetal disc or internal contacts have likely failed.

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.