Lennox 34M74 Pressure Switch

The Lennox 34M74 Pressure Switch is a critical safety component engineered for precision monitoring of combustion air in residential and commercial HVAC systems. This OEM Lennox replacement part features a single pole, single throw (SPST) electrical configuration, meticulously calibrated to an actuation point of .33" WC (inches water column). Designed with a standard 1/4" barb connection, it ensures a secure, leak-proof interface with the inducer housing or pressure tubing. The Lennox 34M7401 is technically identical to this unit, allowing for seamless integration into existing Lennox furnace control circuits. By accurately detecting pressure differentials, this 0.33" WC pressure switch prevents the ignition sequence if the venting or combustion air flow is obstructed, protecting the internal heat exchanger and ensuring efficient unit operation. For veteran technicians, this SPST pressure switch offers a reliable high-quality solution for restoring furnace safety parameters to factory specifications without the risk of generic compatibility issues.

• Factory-Calibrated Precision: Fixed .33" WC set point ensures the combustion blower is providing adequate airflow before the gas valve is energized.
• Direct OEM Compatibility: Verified as an exact replacement for the Lennox 34M7401, maintaining the integrity of the original system design.
• Durable Construction: Built to withstand the high-cycle demands of modern high-efficiency furnaces and environmental stressors within the cabinet.
• Simplified Installation: Standard 1/4 inch barb and SPST wiring allow for rapid field replacement during service calls.

What are the symptoms of a failing Lennox 34M74 pressure switch?
Common signs include the furnace failing to ignite while the inducer motor is running, or the control board throwing a specific flash code indicating a pressure switch circuit stuck open or closed.

Is the 34M74 interchangeable with other pressure ratings?
No. For safety and performance, you must use a switch with the exact 0.33" WC rating specified by the manufacturer to ensure proper draft and combustion safety.

Does this switch include the 1/4" tubing?
This part is the switch assembly only. We recommend inspecting your existing silicone tubing for cracks or debris during the installation of the new Lennox 34M74.

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.