Trane CNT3670 Limit Switch

The Trane CNT3670 is an essential OEM high limit switch designed for American Standard and Trane gas furnaces. This L225F CO limit switch functions as a critical safety component, monitoring the heat exchanger temperature to prevent dangerous overheating. Featuring a Single Pole Single Throw (SPST) configuration, the circuit is normally closed and triggers an open state when internal temperatures reach the 225-degree Fahrenheit trip point. Proper furnace limit switch replacement ensures that the combustion process is halted immediately if airflow is restricted, protecting the primary heat exchanger from thermal stress and potential cracks.

For veteran technicians, the CNT3670 is a direct-fit solution for furnace short cycling issues or instances where the blower fan runs continuously due to a tripped safety loop. This fixed temperature disc switch is rated for 15 amps at 125/250 VAC, ensuring reliable electrical performance in demanding HVACR environments. When diagnosing Trane furnace error codes such as the common 4-flash "open limit" signal, verifying continuity across this switch is a standard step in the troubleshooting process. Its 225F cutout rating is specifically calibrated for high-efficiency systems where precise thermal management is mandatory for operational safety.

Key Benefits

• OEM Compatibility: Precision-manufactured as an authentic Trane replacement part for guaranteed fit and function within Trane and American Standard air handlers.
• High Thermal Threshold: Calibrated with an L225F set point to provide a robust safety margin against heat exchanger overheating.
• Electrical Reliability: Features an SPST design capable of handling 15A loads, providing consistent switching performance over thousands of cycles.
• Safety Compliance: Helps maintain system integrity by preventing the gas valve from remaining energized if the plenum temperature exceeds safe limits.

Common Questions

What causes the CNT3670 to trip frequently?
Frequent tripping is typically caused by restricted airflow, such as a clogged furnace filter, blocked return ducts, or a failing blower motor. If the switch remains open even after the system cools, the internal contacts may have failed, requiring a replacement.

Does this switch require a manual reset?
The Trane CNT3670 is generally an automatic reset limit switch, meaning it should close the circuit once the heat exchanger temperature drops below its reset differential. If it does not reset, check for debris or physical damage to the disc.

How can I verify if this limit switch is bad?
Use a multimeter to check for continuity across the terminals while the system is cool. A lack of continuity in a "cold" state indicates a failed internal SPST contact, necessitating a limit switch replacement.

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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.