Lennox 42J04 Limit Switch

The Lennox 42J04 Limit Switch is a critical OEM replacement part designed for high-limit thermal protection in residential and commercial HVAC systems. Engineered to maintain safe operating parameters, this 135-175F Auto Limit Switch features an automatic reset mechanism that interrupts the heating circuit if internal plenum temperatures exceed the 175°F threshold, preventing heat exchanger damage and ensuring system safety. This fixed temperature switch is a direct replacement for legacy part number 42J0401, offering a 1:1 fit for Lennox, Armstrong, and Ducane furnaces. As a veteran technician knows, a failing limit switch is often the culprit behind a furnace short cycling or "limit-tripping" errors on the furnace control board. Utilizing a genuine Lennox part ensures that the calibration matches the original factory response times, maintaining the safety limit circuit integrity without the nuisance tripping common in universal alternatives. This heavy-duty bimetal switch is built to withstand the rigorous thermal cycling of high-efficiency heating units.

• Precise Thermal Calibration: Factory-set to trip at 175°F and reset at 135°F for consistent safety performance.
• Universal Compatibility: Fully interchangeable with part numbers 42J0401, 203542, and 60TI3.
• Automatic Reset: Eliminates the need for manual intervention once temperatures return to the 135°F safety range.
• Durable OEM Construction: Built by Lennox to match the exact specifications required for Lennox and Allied Air branded equipment.
• Easy Integration: Standard snap-action design with secure spade terminals for fast field replacement.

Is the 42J04 compatible with my older 42J0401 switch?
Yes. The Lennox 42J04 is the current OEM replacement and is physically and technically identical to the 42J0401 model.

What are the symptoms of a faulty furnace limit switch?
Typically, a failed switch will cause the blower motor to run continuously or result in the furnace short cycling. If the switch stays open, the burners will not ignite as the safety circuit remains broken.

Can I use this for other brands like Armstrong or Ducane?
Yes. Because Lennox is the parent company for Armstrong Air and Ducane, this part is the approved OEM limit switch for many models within those brands.

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.