Description
Lennox 34M77 Pressure Switch Overview
The Lennox 34M77 is an OEM-grade pressure switch engineered to deliver reliable draft-pressure sensing and safety protection in Lennox furnace and HVAC systems. With a precisely calibrated set point of -1.00″ water column (w.c.), this switch monitors inducer and venting system pressure to ensure safe combustion operation — shutting down the system if proper draft pressure is not established or maintained.
Key Features
- Set point: -1.00″ w.c. (water column)
- Switch type: SPST (Single Pole, Single Throw)
- Connection: 1/4″ barb fitting for secure hose attachment
- Designed as a direct OEM replacement for compatible Lennox furnace models
- Monitors inducer motor and venting system pressure for safe furnace operation
- Prevents furnace operation if adequate draft pressure is not detected
How It Works
The 34M77 pressure switch senses the negative pressure created by the draft inducer motor during furnace operation. When the inducer establishes the correct draft at or beyond the -1.00″ w.c. threshold, the SPST contacts close, signaling the control board to proceed with ignition. If draft pressure falls outside the safe operating range — due to a blocked flue, failed inducer, or venting issue — the switch opens, locking out the furnace and protecting against unsafe combustion conditions.
Application
- Replacement pressure switch for Lennox gas furnaces
- Compatible with systems requiring a -1.00″ w.c. SPST pressure switch
- Suitable for residential and light commercial Lennox furnace applications
Why Choose the Lennox 34M77?
Using the correct OEM-specified pressure switch ensures your furnace operates within manufacturer safety parameters. The 34M77’s 1/4″ barb connection provides a positive, leak-free hose attachment, while the SPST design integrates seamlessly with standard furnace control board wiring. Trust this genuine Lennox replacement part to restore proper safety circuit function and extend the service life of your heating system.
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