Trane SWT1935 Limit Switch

For service calls involving high-temperature safety circuits, the Trane SWT1935 Limit Switch provides critical protection against heat exchanger failure. This OEM Trane replacement part, also identified by manufacturer number C340056P19, is a normally closed, SPST auto-reset limit switch specifically engineered for residential and light commercial Trane and American Standard furnaces. With a 7-inch insertion length, this probe reaches deep into the supply plenum to accurately monitor internal air temperatures.

The Trane SWT1935 features a precise thermal response profile with a 120°F cut-out (open) and a 90°F cut-in (close) temperature. This 30-degree differential prevents rapid cycling while ensuring the blower fan appropriately cools the system before the burners re-ignite. Rated for 5.8 FLA and 34.8 LRA at 120V, this heavy-duty component replaces older or failing high limits that cause frequent system lockouts or "Code 4" errors on the control board. For veteran techs, the SWT1935 furnace limit switch is the standard solution for restoring safe furnace operation when airflow restrictions or dirty filters have stressed the original safety controls.

• Precise Thermal Calibration: Factory-set to open at 120°F and automatically reset at 90°F, eliminating the need for manual intervention during standard operation.
• Optimal Probe Depth: The 7" insertion design ensures the sensor captures the most accurate temperature reading within the air stream, reducing nuisance trips.
• Broad Compatibility: Directly compatible with a wide range of Trane and American Standard models, including AUD, ADD, and TDD series gas furnaces.
• Industrial Build Quality: Constructed by ServiceFirst to withstand high-cycle environments, mitigating the risk of premature contact wear or corrosion.
• Easy Installation: Features standard tab terminals for quick wiring and a flat mounting flange typical of HVAC high-limit safety devices.

How do I verify if my Trane limit switch is faulty?
Using a multimeter, check for continuity across the terminals when the switch is cool. If the circuit is open at room temperature, the internal bimetal disc is likely damaged and requires replacement. Ensure you also check for restricted airflow, as a tripped switch often points to a clogged HVAC filter or a failing blower motor.

Will the Trane SWT1935 fix a furnace that is short-cycling?
If the furnace runs for several minutes and then shuts down the burners while keeping the blower on, the high limit switch is doing its job. Replacing the SWT1935 solves the issue ONLY if the switch has weakened or drifted from its setpoints. Always inspect the heat exchanger and air filters first to confirm the trip isn't caused by actual overheating.

Are there any cross-reference parts for the C340056P19?
This part is a direct replacement for the SWT1935 and is used in place of various factory-installed 120/90 degree limit switches. Verify the insertion length and temperature ratings match your specific model's data plate before installation.

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.