Lennox 33H78 Limit Switch

The Lennox 33H78 Limit Switch is a critical OEM furnace safety control engineered for precise thermal monitoring in residential and commercial Lennox heating systems. Labeled with an L130-20F temperature rating, this high-limit switch is designed to open the electrical circuit at 130°F and automatically reset when the temperature drops 20°F. As a vital HVAC replacement part, it prevents heat exchanger damage and hazardous conditions by interrupting the burner circuit if airflow is restricted or the blower motor fails. Technicians frequently utilize the 33H78 to resolve primary limit trip codes and ensure Lennox furnace compatibility across various gas-fired units. This genuine Lennox part provides exact factory specifications, ensuring the system operates within established safety parameters without nuisance tripping or delayed response times.

Key Benefits for Contractors

• Direct OEM Replacement: Matches Lennox 33H78 factory specs for seamless integration into existing wiring harnesses.
• Precise Thermal Calibration: Fixed 130°F cut-out and 110°F cut-in (L130-20F) provides reliable overheat protection.
• System Safety Integrity: Protects the heat exchanger and critical internals from thermal stress and potential cracks.
• Field Efficiency: Standard mounting footprint and terminal configuration allow for fast installation and reduced downtime.

Common Questions

What causes a Lennox 33H78 limit switch to trip repeatedly?
Frequent tripping is usually indicative of restricted airflow, such as a clogged HVAC filter, dirty secondary heat exchanger, or a failing blower capacitor, rather than a faulty L130-20F switch.

Is the 33H78 switch a manual or automatic reset?
The 33H78 is an automatic reset limit switch; it will close the circuit once the plenum temperature cools down by the 20-degree differential.

Can I substitute this with a universal limit switch?
While universal parts exist, using this genuine Lennox OEM safety control ensures the exact insertion length and thermal response time required by the original equipment manufacturer.

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.