The Carrier HH19ZA940 Auto Limit Switch is a temperature-regulating safety control designed for HVAC systems, operating within a range of 85°F to 140°F. It functions by automatically opening or closing the electrical circuit in response to temperature changes, preventing overheating and maintaining safe operation. Commonly used in furnaces, air handlers, and heating units, it protects vital components from thermal damage. This switch enhances system reliability, supports energy efficiency, and extends equipment lifespan, making it a dependable solution for consistent and safe HVAC performance in residential and commercial applications.