Williams 7735 Limit Switch

The Williams 7735 Limit Switch is a critical OEM replacement part designed for high-temperature safety regulation in Williams Forsaire Counterflow top-vent furnaces. Engineered with a 330F fixed temperature setpoint and a 5-inch insertion depth, this high-limit safety control ensures the combustion chamber does not exceed safe operating parameters. When air temperature reaches the 330°F threshold, the switch opens the electrical circuit to the gas valve, preventing heat exchanger damage and ensuring system integrity. This auto-reset limit switch is specifically compatible with Forsaire models including the 3508231, 3508632, and 5008631 series. For technicians performing a furnace limit switch replacement, this component provides the exact thermal response curve required by the original manufacturer. Its robust construction and precise thermal cutout calibration make it a reliable choice for maintaining secondary heat protection in residential and commercial counterflow applications.

Key Benefits for Technicians

• Precise Thermal Protection: Fixed 330°F trip point provides immediate circuit interruption during over-temperature events to protect the heat exchanger.
• Exact OEM Fit: Features a 5" probe insertion length, ensuring compatible placement within the airflow path of Williams Forsaire furnaces.
• Automatic Reset Logic: The 7735 limit control automatically resets once temperatures drop below the safety differential, reducing unnecessary service calls for temporary spikes.
• Durable Construction: Built to withstand the harsh environment of a furnace combustion chamber for long-term HVAC safety compliance.

Common Questions

How do I know if my Williams 7735 limit switch is bad?
If your furnace blower runs continuously but the burners won't ignite, or if the system cycles off before reaching the thermostat setpoint, use a multimeter to check for continuity across the terminals. A tripped limit switch will show an open circuit when the furnace is cold.

What causes this 330F limit switch to trip repeatedly?
Frequent tripping usually indicates restricted airflow. Check for a clogged HVAC air filter, blocked return ducts, or a failing blower motor. If airflow is optimal and the switch still opens at low temperatures, the internal bimetal disc may have fatigued, requiring a replacement 7735 switch.

Can I use a shorter insertion length switch as a substitute?
No. The 5-inch insertion length is engineered to sense temperature at a specific point in the heat exchanger. Using a shorter probe may result in delayed response times, potentially allowing the furnace to overheat before the safety circuit activates.

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.