KSD303-B series snap-action defrost thermostat is a kind of miniature waterproof and hermetically seal bimetal thermal protector. It is of single-pole single-throw structure and works under resistive load. Thermostat is enveloped in cold-resistant and flame-retardant plastic tube or sealing gum for possible underwater applications. The product series is widely used as heating compensated switch or automatic defrosting control switch in air-cooling frostless refrigerators.

According to different structures, KSD303 series is divided into five sub series as: KSD303-A, KSD303-B, KSD303-C, KSD303-D.