The Whirlpool WP67003426 Refrigerator Defrost Thermostat monitors evaporator temperature to regulate the defrost cycle and control frost buildup. It activates or interrupts the defrost heater according to temperature changes, supporting effective ice removal and consistent cooling. This component maintains proper temperature sensing within the defrost system and supports reliable refrigerator performance. A defective thermostat may cause excessive frost accumulation, incomplete defrosting, or cooling issues. Replacing a faulty unit can restore temperature-based defrost control and maintain proper freezer conditions. Before purchasing, check your refrigerator’s model number to verify compatibility and ensure the replacement thermostat fits your appliance.