Lennox 38M07 Limit Switch

The Lennox 38M07 Limit Switch is a critical safety component designed for precise thermal regulation within residential and commercial HVAC systems. This genuine OEM Lennox part (MPN: 38M07) features a 3-inch insert length and operates as a normally closed switch, ensuring the circuit remains engaged during standard operation. Engineered to prevent heat exchanger damage and unsafe operating conditions, this 135-165F AUTO limit switch automatically opens the circuit when the internal plenum temperature reaches 165°F. Once the system cools to 135°F, the switch executes an automatic reset, allowing the ignition sequence to resume. This high-limit control is frequently utilized in Lennox G40UH series furnaces and compatible equipment from Allied, Armstrong, and Ducane. Replacing a drifting or fouled fixed temperature limit control is essential for resolving E250 error codes and preventing system short-cycling. Its robust mechanical design ensures reliable overheat protection and maintains high-efficiency performance for veteran HVAC contractors and service technicians.

Key Benefits for Technicians:

• Sensing Accuracy: Factory-calibrated to open at 165°F and reset at 135°F for consistent thermal protection.
• Broad Compatibility: Direct replacement for several furnace high limit models across Lennox, Concord, and Magic-Pak lines.
• Durable Construction: Features a high-grade 3-inch probe designed to withstand rapid temperature fluctuations in the supply plenum.
• Safety Compliance: Acts as a primary normally closed limit switch to prevent cabinet overheating and potential heat exchanger failure.
• Simplified Installation: Standard 38M07 mounting footprint allows for rapid field replacement during emergency service calls.

Common Questions:

What causes a Lennox 38M07 to trip frequently?
Frequent tripping is usually indicative of restricted airflow. Check for a dirty air filter, blocked return air ducts, or an impacted evaporator coil. If airflow is optimal, the switch may be "drifting" and require replacement.

How do I test the 38M07 limit switch for failure?
With the power off, use a multimeter to check for continuity across the terminals. Since this is a normally closed component, it should show zero resistance at room temperature. An "open" reading under 165°F indicates a failed switch.

Can I use this as a replacement for other Lennox limit switches?
Only if the temperature specifications and insert length match. Using a switch with a higher opening point than the 165°F rating of the 38M07 can compromise system safety and lead to equipment damage.

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.