Lennox 87H92 Limit Switch

For service technicians working on older Lennox, Allied, or Ducane heating units, the Lennox 87H92 Limit Switch is a critical safety component. This 100-140F AUTO Limit Switch is an SPST (Single Pole Single Throw) device designed to maintain air temperature within the plenum. The 87H92 is identical to 20121901 and serves as a direct OEM replacement parts solution for a variety of residential furnace series, including Lennox G24, G26, AF80MPA, and GH19 models. As a primary high limit control, it monitors the heat exchanger for overheating symptoms and will automatically open the circuit to de-energize the gas valve if temperatures exceed the 140°F threshold. Its automatic reset functionality ensures the system resumes operation once the internal temperature drops back to 100°F, preventing permanent damage to the heating assembly. Using a genuine Lennox 87H92 replacement ensures proper HVAC part compatibility and prevents the common "blower fan stuck on" or "short cycling" issues often caused by out-of-spec aftermarket alternatives.

Key Benefits

• Precise Thermal Calibration: Engineered with a fixed 140°F open and 100°F close setpoint to ensure the furnace limit switch trips only when necessary.
• Broad Compatibility: Cross-references directly with Lennox 20121901, 92L18, and several Allied/Armstrong part numbers (R20001104, 20054604).
• Automatic Reset Logic: Eliminates the need for manual intervention after a temporary overheat event, restoring heat once safe parameters are met.
• Professional Grade Durability: Specifically built for the high-cycle environments of Lennox G24 and G26 furnace series vestibule panels.

Common Questions

When a high limit switch like the 87H92 detects an overheat condition (above 140°F), it opens the circuit to the gas valve while simultaneously signaling the furnace control board to run the blower. If the blower runs indefinitely without flame, the switch may be stuck open or the system is failing to cool down due to a restriction.

Yes. Low airflow is the primary cause of furnace short cycling. A clogged filter or blocked return air vents reduces the volume of cool air passing over the heat exchanger, causing internal temperatures to spike and trip the 87H92 limit switch protection circuit.

Correct. The 87H92 is identical to 20121901 in both physical dimensions and technical specifications. It is a one-to-one OEM substitute that requires no modification to the wiring harness or mounting plate.

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.