1.Working Principle Internal NTC thermistor core: Low temperature → High resistance High temperature → Low resistance The control board provides a fixed reference voltage. It calculates the actual temperature by detecting resistance changes and adjusts the compressor and heating wire accordingly. Universal Standard Parameters R25: 10kΩ / 5kΩ (most common) B value: 3435K / 3950K Temperature accuracy: ±0.5℃ ~ ±1℃ Operating temperature: -40℃ ~ 125℃ 2. Two Main Types for Air Conditioners 1. Room Temperature Sensor (Ambient Sensor) Probe wrapped with plastic shell, exposed to indoor air flow Function: Detect indoor ambient temperature Control logic: When room temp reaches set value, compressor slows down or stops 2. Evaporator Coil Pipe Temperature Sensor (Pipe Sensor) Metal copper tube probe, clamped tightly on air conditioner copper pipeline Core functions: Anti-freeze protection: Prevent evaporator from icing up Defrost control for heating mode Overload protection for compressor 3. Structure NTC thermistor chip (epoxy / glass sealed) Probe: Plastic ambient head / copper tube pipe head High temperature resistant PVC silicone wire Optional heat shrink tube, fixed buckle, JST terminal plug 4. Main Functions Constant temperature control for cooling & heating Evaporator anti-icing protection Outdoor unit automatic defrost (heat pump AC) Compressor over-temperature safety protection Indoor temperature display on panel 5. Common Fault Phenomena Air conditioner runs but cannot cool or heat well Compressor frequently starts and stops Evaporator freezes heavily Display error code, machine locked and unable to work Indoor temperature inaccurate, inconsistent with set value 6. Application Range Household split air conditioner, cabinet air conditioner, inverter air conditioner, central air conditioning, vehicle air conditioner, mobile air cooler, dehumidifier