Description
The Lennox 51W90 is an OEM replacement pressure switch engineered for precise, dependable performance in Lennox furnace and air handler applications. Designed to monitor negative pressure generated by the inducer motor, this switch helps protect the heat exchanger and ensures safe furnace operation by verifying proper draft before allowing ignition to proceed.
Key Features
- Set point: -0.65″ water column (“wc) — factory-calibrated for accurate pressure sensing
- SPST (Single-Pole, Single-Throw) switching action for straightforward open/close control
- Dual 1/4″ barb connections for easy hose attachment and secure, leak-free sealing
- Direct OEM replacement for compatible Lennox furnace models — no modifications required
- Monitors inducer motor draft to confirm safe operating conditions before ignition
- Compact, rugged construction built to withstand the demands of residential and light commercial HVAC systems
How It Works
The pressure switch senses the negative pressure (vacuum) created by the draft inducer motor. When the inducer achieves the correct airflow, the switch closes, signaling the control board to proceed with the ignition sequence. If adequate draft is not detected — indicating a blocked flue, failed inducer, or cracked heat exchanger — the switch remains open, locking out ignition and preventing unsafe operation.
Application
- Designed for use in Lennox gas furnaces requiring a -0.65″wc pressure switch
- Ideal for service technicians performing OEM-quality repairs and replacements
- Compatible with systems utilizing 1/4″ rubber or silicone pressure tubing
Why Choose the Lennox 51W90?
Using a genuine OEM-equivalent replacement pressure switch ensures your Lennox system operates within its designed safety parameters. The 51W90 delivers the precise setpoint, connection type, and switching characteristics needed to restore full, safe furnace functionality — minimizing callbacks and maximizing customer confidence.
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