The Heatcraft Refrigeration 21340101 Defrost Timer prevents frost buildup and ensuring optimal performance of your HVAC system. This electromechanical device cycles between defrost and normal operation phases based on preset time intervals or temperature triggers. During defrost, the timer activates heating elements to melt accumulated ice on evaporator coils, maintaining efficient heat transfer. Once defrosting is complete, the timer switches back to normal operation, allowing the evaporator to cool the air again. It's commonly found in cold storage facilities, walk-in coolers and freezers, supermarket display cases, and industrial process cooling applications. By preventing frost buildup, the defrost timer safeguards food quality, product integrity, and system efficiency, contributing to overall HVAC system health and longevity.