Lennox 10M74 Limit Switch

The Lennox 10M74 Limit Switch is a critical fixed-temperature safety control designed for precise thermal monitoring within Lennox residential furnaces. Functioning as a normally closed (NC) switch, this component features a 155°F cutout and a 125°F reset (155F-OUT 125F-IN), ensuring the burner circuit opens if plenum temperatures exceed safe operating limits. Also identified by the manufacturing part number 10M7401, this limit control replacement is engineered for specific insertion depths to maintain accurate sensing within the airflow stream. For technicians performing furnace troubleshooting, verifying the Lennox 10M74 specifications is essential for restoring system safety and preventing heat exchanger damage. This HVAC high limit switch provides a drop-in fit for compatible Lennox furnace parts, maintaining the original equipment manufacturer's calibrated trip points for reliable flame rollout and over-temperature protection during demanding heating cycles.

• Precise Thermal Calibration: Fixed 155°F open and 125°F close setpoints prevent nuisance tripping while ensuring furnace over-temperature protection.
• Direct OEM Interchangeability: Fully compatible with part number 10M7401, facilitating seamless Lennox 10M74 installation without bracket modifications.
• Enhanced System Safety: Protects the heat exchanger and surrounding components by interrupting the 24V furnace control circuit upon detecting excessive heat.
• High-Grade Construction: Built to withstand the constant thermal cycling typical of high-efficiency gas furnaces and electric air handlers.

What causes a Lennox 10M74 limit switch to trip frequently?
Frequent tripping usually indicates restricted airflow, often caused by a dirty air filter, blocked return ducts, an undersized evaporator coil, or a failing blower motor. If the switch remains open after the plenum cools, the internal bimetal disc may have failed.

Can the 10M74 be used in place of a different temperature-rated switch?
No. You must match the Lennox limit switch temperature rating exactly. Replacing a 155°F switch with a higher rating can lead to hazardous conditions and heat exchanger fatigue.

Is the 10M74 a manual or automatic reset switch?
The 10M74 is an automatic reset limit switch. It will automatically close the circuit once the sensed temperature drops back down to the 125°F reset point.

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.