Lennox 51W90 Pressure Switch

The Lennox 51W90 Pressure Switch is a critical safety component designed for precise combustion air monitoring in high-efficiency gas furnaces. Engineered with a set point of -.65"wc, this SPST (Single Pole Single Throw) switch ensures the inducer motor is generating sufficient vacuum before allowing the ignition sequence to proceed. As a genuine OEM replacement part, it offers a direct fit for Lennox G43UF and G51MP series units, maintaining the original equipment’s safety calibrations without the need for field modifications. The assembly features dual 1/4" barb connections for secure pneumatic tubing attachment and an integrated mounting bracket for rapid installation. Utilizing a high-quality furnace pressure sensor like the 51W90 prevents common HVAC 6 red flashes or pressure switch lockout codes often caused by diaphragm failure or restricted venting. This HVAC combustion air switch is essential for technicians performing furnace troubleshooting to restore reliable heating performance and verify proper ventilation across various Lennox-built residential platforms.

• Broad Compatibility: Engineered as a drop-in OEM Lennox part for popular G43 and G51 series furnaces and compatible Armstrong or Concord models.
• Precision Calibration: Factory-preset at -.65"wc to ensure 100% accurate vacuum detection and safe manifold pressure operation.
• Durable Construction: Built with high-grade internal diaphragms to resist condensation build-up and prevent premature mechanical failure in high-cycle environments.
• Simplified Installation: Features dual 1/4" barb terminals and a pre-installed bracket for direct-to-collector box mounting.

• How do I resolve a 'Pressure Switch Open' error on a Lennox furnace? Inspect for blocked flue pipes, clogged condensate drains, or debris in the pressure switch hose. If the inducer is running but the 51W90 fails to close, the internal diaphragm may be ruptured.
• Does it matter which side of the dual barb connection I use? Yes. In a vacuum system, you must follow the negative and positive port labeling on the switch body to ensure the -.65"wc set point is accurately triggered.
• Can I use this switch for high-altitude applications? Always cross-reference the Lennox 51W90 specific pressure rating with your technical service manual, as higher elevations often require different WC thresholds to account for thinner air density.

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.