1.Working Principle Built-in NTC thermistor core: Low temperature → high resistance; High temperature → low resistance The control board calculates actual temperature via resistance changes to control compressor startup/shutdown, automatic defrost and over-temperature protection. 2. Universal Standard Parameters R25 resistance: 5kΩ / 10kΩ (most mainstream models) B-value: 3435K, 3950K Accuracy: ±0.5℃ ~ ±1℃ Operating temperature: -40℃ ~ 80℃ Anti-freezing, anti-moisture, anti-condensation design 3. Two Main Types & Structure Type 1: Ambient Cabinet Sensor (Fridge/Freezer Room Temp) Small plastic sealed probe, hung inside the storage compartment Short thin wire, small fixed buckle Detect air temperature inside fridge cavity to control cooling cycle Type 2: Evaporator Defrost Temperature Sensor Copper tube probe with fixed clip, clamped on evaporator coil Key for automatic defrost logic Structure: Glass sealed NTC chip + copper tube head + high-low temperature resistant PVC wire + terminal plug 4. Core Functions Constant temperature storage control When cabinet temperature rises above set value, compressor starts cooling; stop cooling once target temperature is reached. Separate sensors for fridge (2~8℃) and freezer (-18℃ standard). Automatic evaporator defrost control Detect evaporator frost temperature to trigger defrost heater; stop defrost when frost melts completely to avoid overheating cooling system. Over-temperature alarm If internal temperature rises abnormally (door left open, compressor failure), panel prompts temperature error warning. Anti-freeze protection Prevent food from being over-frozen in refrigerating compartment. 5. Common Fault Symptoms Compressor runs non-stop, fridge too cold or cannot cool down Evaporator accumulates thick frost, defrost function fails Refrigerator temperature display inaccurate Machine reports temperature error code and stops cooling Food freezes solid in fresh food compartment 6. Application Range Household single-door / double-door / multi-door refrigerators, vertical freezers, chest freezers, wine refrigerators, commercial display refrigerators, ice makers