Lennox 24L51 Pressure Switch

The Lennox 24L51 Pressure Switch is a critical OEM safety component engineered for precise airflow monitoring in Lennox residential and light commercial gas furnaces. This induced draft pressure switch features a single-pole, single-throw (SPST) configuration factory-set to a 0.51" WC (water column) trip point. Designed for high-accuracy sensing, it utilizes a 1/4" barb connection for seamless integration with standard vacuum tubing and includes an integrated mounting bracket for secure installation within the blower compartment or vestibule.

For technicians servicing 80MGF series units or other compatible forced-air systems, the Lennox 24L51 serves as a direct-fit HVAC replacement part that ensures the inducer motor is moving sufficient combustion air before the ignition sequence begins. Its normally open contacts close upon detecting the specified negative pressure, preventing unsafe burner operation in the event of a blocked flue or restricted heat exchanger. Utilizing this furnace pressure switch maintains the original equipment’s pressure differential specifications and UL safety listings.

• OEM Precision: Guaranteed 0.51" WC set point ensures exact compliance with Lennox blower deck specifications.
• Corrosion Resistance: Engineered with high-grade housing materials to withstand the acidic condensate often found in flue gas environments.
• Drop-In Installation: Features a factory-aligned bracket and standard 1/4" barb connection to reduce diagnostic and repair time.
• System Security: Prevents combustion cycles under restricted venting conditions, protecting the heat exchanger from thermal stress.

What causes a Lennox 24L51 to fail?
Failure is typically caused by moisture buildup in the sensing lines, a ruptured internal diaphragm, or carbon buildup at the 1/4" barb connection. Always inspect the vacuum tubing for cracks when replacing the switch.

Is this switch compatible with 2-stage furnaces?
The 24L51 is an SPST single-stage switch. It is designed for specific pressure duties and should not be used as a substitute for multi-stage or different "WC rated switches, even if the physical footprint is similar.

How do I verify if the switch is tripping correctly?
Use a manometer to confirm the inducer is pulling at least 0.51" WC at the pressure port. If the pressure is sufficient but the Lennox 24L51 contacts remain open, the switch requires replacement.

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.