Lennox 42J04 Limit Switch or blocked return air grilles

or blocked return air grilles that cause heat to build up beyond the 155°F threshold

ensuring precise equal percentage flow characteristics in demanding hydronic and steam applications

Key Technical Benefits

How do I install the anti-rotation bracket correctly

Lennox 42J04 Limit Switch or blocked return air grillesThe 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 175F threshold, preventing heat exchanger damage and ensuring system safety. This fixed temperature