Lennox 34M77 Pressure Switch

Ensure reliable sequence of operation with the Lennox 34M77 Pressure Switch, a critical safety component designed for heating and cooling systems. This OEM Lennox furnace pressure switch is engineered to monitor draft pressure and confirm proper inducer motor performance before allowing the ignition process to begin. Featuring a precise -1.00"wc SPST (Single Pole Single Throw) configuration, this switch actuates at 1.00" W.C. and resets at 1.15" W.C., effectively preventing combustion under unsafe venting conditions.

The Lennox 34M77 is built for durability with a 1/4" barb connection for secure pneumatic tubing attachment and is rated for 5 Amps at 24 VAC. As a direct replacement for Lennox 60J54 and 85K37, it offers versatile compatibility across various Lennox and Allied Air unit heaters and furnaces. Technicians typically find this part in popular models like the LF24 series. Utilizing genuine Lennox HVAC parts like the 34M77 ensures that your equipment maintains its original factory specifications and provides dependable safety interlocking in residential and commercial applications.

• Precise Pressure Calibrations: Factory-set at -1.00" W.C. to Ensure accurate inducer fan verification.
• Broad Compatibility: Direct substitute for legacy part numbers including 60J54, 85K37, and 65289100.
• Contractor-Grade Reliability: Robust SPST normally open contact design capable of handling 5A resistive loads.
• Standardized Installation: Features a universal 1/4" barb connection for fast, leak-free hose integration.

What are the symptoms of a failing Lennox 34M77 pressure switch?
Common indicators include the furnace inducer motor running without ignition, or the system triggering a pressure switch lockout code (often 2 or 3 blinks on the control board), indicating the circuit failed to close or stayed closed.

Can I use an adjustable pressure switch to replace the 34M77?
For safety and performance, it is highly recommended to use the 34M77 1.00" WC fixed switch to match the exact static pressure requirements of the original heat exchanger design.

What is the purpose of the 1/4" barb connection on this switch?
The 1/4" barb serves as the pneumatic interface, allowing the switch to sense the negative pressure generated by the draft inducer via a flexible silicone or rubber tube.

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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.