A limit switch is a safety device that automatically opens an electrical circuit when temperature or pressure reaches a preset threshold. Commonly installed in furnaces and air handlers, limit switches prevent equipment from overheating or operating at dangerous pressures. They typically reset automatically when conditions return to normal operating ranges.
Technical Specifications
Limit switches in furnaces operate at temperature settings between 120°F and 200°F, depending on equipment type. High-limit switches on furnaces typically activate at 200°F to 220°F, while low-limit switches on air handlers engage around 70°F to 90°F. These devices use bimetallic strips or mercury bulbs to detect temperature changes and break electrical connections.
Safety and Maintenance
Limit switches protect HVAC equipment from thermal stress and component damage. Regular inspection ensures proper operation, as stuck or malfunctioning switches can cause system shutdowns or safety hazards. Annual furnace maintenance should include limit switch testing to verify response at correct temperatures.