Armstrong Furnace R40154B004 Auto Limit Switch 140°F-170°F

The Armstrong Furnace R40154B004 Auto Limit Switch 140F170F is a temperature safety control component used in furnace systems to monitor heat levels within the heat exchanger or supply air stream. It operates by opening or closing an electrical circuit within a defined temperature range and supports regulating system response when internal temperatures rise beyond normal operating limits in HVAC systems. It is installed in furnace assemblies, where it against overheating by interrupting burner operation and allowing the system to cool before restarting. The switch supports safe furnace operation by maintaining controlled temperature cycling and avoiding excessive heat buildup during heating demand.