Lennox 87H90 Limit Switch

The Lennox 87H90 Limit Switch is a critical OEM furnace replacement part engineered for precise thermal regulation within high-performance heating systems. This primary limit control features a 1.75-inch insertion length and operates on an automatic reset logic, making it essential for maintaining safe internal plenum temperatures. As a veteran technician knows, this SPST (Single Pole Single Throw) safety device is designed to open on rise at 190°F and automatically re-close at 150°F, ensuring the Lennox furnace high limit circuit remains secure during peak demand. Cross-referencing reveals compatibility with several older Ducane, Allied Air, and Aire-Flo models, often replacing discontinued part numbers such as 52M44, 87H9001, and 20001102. When troubleshooting a system that is short-cycling or throwing an E250 error code, replacing a worn high limit switch is standard procedure to restore reliable HVAC safety switch operation and prevent nuisance shutdowns caused by thermal fatigue in the original component.

Key Benefits for Contractors:

• Broad Compatibility: Directly replaces multiple legacy part numbers including 92L17, 52M4401, and R20001102 for streamlined inventory management.
• Precision Calibration: Narrow 40-degree differential (190°F Open / 150°F Close) ensures accurate furnace overheating protection without premature tripping.
• Durable Construction: Built with a rugged housing and high-grade internal contacts to withstand the harsh environments of industrial and residential HVAC heat exchangers.
• Plug-and-Play Installation: Standard 1/4-inch male quick-connect terminals allow for fast field retrofits on existing wiring harnesses.

Common Questions & Troubleshooting:

• Why is my furnace short-cycling or hitting the high limit? While a failing Lennox 87H90 can cause this, always verify airflow first. Check for clogged filters, blocked return air grilles, or a failing blower motor before condemning the switch.
• Does the insertion length matter? Yes. This model features a 1.75-inch probe. Installing a switch with the incorrect length can lead to inaccurate temperature sensing and potential safety hazards.
• Can I use this to replace a manual reset switch? No. This is an auto-reset limit switch. Always match the reset type and temperature specifications found on the original equipment manufacturer's data 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.