Trane CNT3785 Limit Switch

The Trane CNT3785 Limit Switch is a heavy-duty, OEM replacement part engineered for precise thermal regulation in commercial gas-electric packaged units. This Single Pole Single Throw (SPST), normally closed (NC) switch is factory-calibrated to open at 170°F, effectively interrupting the burner circuit to prevent heat exchanger damage during high-temperature events. Featuring an 11-inch insertion depth, the CNT3785 provides accurate sensing within the supply plenum, ensuring the automatic reset function restores system operation once internal temperatures return to a safe operating range.

Designed for seamless integration with Trane YSC series units, including YSC036G through YSC120H models, this switch eliminates the need for manual resets and reduces nuisance service calls. Its robust construction handles 240V applications, making it a reliable choice for maintaining HVAC system safety and preventing short-cycling caused by restricted airflow or blower failure. For technicians diagnosing a "4-flash" error code or an open limit circuit, the Trane 170f CO Auto Limit Switch offers the exact specifications required for a drop-in furnace limit switch replacement.

• Precise 170°F Trip Point: Protects critical components from overheating with factory-tested accuracy.
• 11" Insertion Sensor: Extended probe length reaches deeper into the air stream for more responsive thermal monitoring.
• Automatic Reset Logic: Streamlines operation by self-correcting after the cool-down cycle, minimizing manual labor.
• OEM Compatibility: Guaranteed fit for Trane and American Standard Voyager and Precedent rooftop units.
• Durable SPST NC Contacts: Engineered for high-cycle reliability in demanding commercial environments.

What causes a Trane CNT3785 to trip frequently?
Repeated tripping is usually indicative of restricted airflow. Check for high static pressure, clogged 2-inch pleated filters, or a failing blower motor capacitor that prevents the fan from reaching full RPM.

Is the CNT3785 compatible with 24V or 240V circuits?
Yes, this switch is designed to operate within standard HVAC control circuits and is rated for up to 240V applications, typically found in commercial integrated control boards.

Can I use a shorter insertion switch instead of the 11-inch model?
It is not recommended. The 11-inch depth is critical for proper positioning in the plenum; a shorter switch may not sense the true internal temperature, leading to delayed safety responses.

This item is not eligible for free shipping.

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.