Description
The Lennox 51W93 is a factory-specified pressure switch engineered for use in Lennox furnace and air handler applications. Designed to monitor negative pressure levels within the venting and inducer circuit, this switch provides a critical safety function — preventing furnace operation if proper draft or combustion airflow conditions are not met.
Key Features
- Set point: -1.12″ water column (“wc) — factory-calibrated for precise trip and reset performance
- SPST (Single Pole, Single Throw) switching configuration for straightforward open/close circuit control
- Dual 1/4″ barb port connections for easy hose attachment to pressure taps on the inducer assembly or collector box
- Direct OEM replacement for compatible Lennox furnace models — ensures proper fit and function without modification
- Compact, durable housing designed to withstand the demands of residential and light commercial HVAC environments
How It Works
The pressure switch monitors the negative pressure (vacuum) generated by the draft inducer motor. When the inducer creates sufficient airflow, the diaphragm inside the switch deflects and closes the electrical circuit, signaling the control board that it is safe to proceed with ignition. If the required pressure differential is not achieved — due to a blocked flue, failed inducer, or cracked hose — the switch remains open, locking out the furnace and protecting against unsafe operation.
Application
- Designed as an OEM replacement for select Lennox gas furnace models
- Compatible with systems requiring a -1.12″wc negative pressure switch
- Suitable for residential and light commercial forced-air heating systems
Installation Notes
- Always verify the set point and port configuration match the original switch before installation
- Inspect all pressure hoses and barb fittings for cracks or blockages during replacement
- Consult the unit’s service manual or wiring diagram to confirm correct wiring of the SPST contacts
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