1. Split-type air conditioners (including wall-mounted and floor-standing units) use NTC (Negative Temperature Coefficient) thermistors for all temperature sensors. This is because NTC thermistors have the perfect characteristics of low cost, high sensitivity, and small size, making them suitable for air conditioning products that are mass-produced and cost-sensitive. Although the type is singular, split-type air conditioners typically include the following types of NTC temperature sensors based on installation location and function.
2. Classification of split-type air conditioner temperature sensors by location and function:
1: Indoor Unit
a. Indoor Environment Temperature Sensor (Room Temperature Sensor)
Location: Installed at the air inlet of the indoor unit (usually behind the filter) to sense the return air temperature of the room. Function: This is the “sensory organ” of the air conditioner. The CPU compares the detected room temperature with the user-set target temperature to determine whether the compressor should start, run, or stop, making it a core component for achieving automatic temperature control. Common failure symptoms: Sensor failure or deviation can lead to the air conditioner not stopping cooling/heating, stopping before reaching the set temperature, or frequent starts and stops.
b. Indoor Evaporator Pipe Temperature Sensor (Pipe Temperature Sensor)
Location: Usually tightly attached to the surface of the indoor unit’s evaporator (copper pipe and fins) with a metal clamp to directly measure the evaporator’s temperature. Function: It plays a very important and multiple role: Cooling freeze protection: During cooling, if the evaporator temperature is too low (e.g., close to 0°C), it indicates possible dirt blockage, lack of refrigerant, or insufficient indoor airflow. The CPU will force the compressor to reduce frequency or stop to prevent ice damage to the machine. Cooling cold wind prevention: At the beginning of heating, the indoor evaporator (which is the condenser at this time) is still cold, and the CPU will delay the start of the indoor fan based on this sensor signal to avoid blowing out cold air. Heating overload protection: During heating, it prevents the condenser temperature from being too high and the pressure from being too great. Defrost control: During heating, it monitors the changes in evaporator temperature to determine the frosting condition of the outdoor unit, thus entering the defrosting program.
2. Outdoor Unit
c. Outdoor Condenser Temperature Sensor
Location: Attached to the fins of the outdoor unit’s condenser.
Function: Used to monitor the temperature of the condenser, participating in defrost logic judgment and overload protection during heating.
d. Outdoor Environment Temperature Sensor
Location: Installed near the air inlet of the outdoor unit. Function: Detects the outdoor environment temperature. The CPU limits the operating frequency of the compressor based on this signal to protect the system from operating safely in extreme weather.
e. Compressor Discharge Temperature Sensor
Location: Installed on the discharge pipe of the compressor, usually fixed with a metal sleeve.
Function: A key protection sensor. It directly monitors the temperature of the discharge pipe to prevent the compressor from being damaged due to excessively high discharge temperatures (caused by lack of refrigerant, system blockage, etc.). If the temperature exceeds the limit, it will immediately force a frequency reduction or shutdown.
f. Compressor Suction Temperature Sensor (equipped in some models)
Location: Installed on the suction pipe of the compressor.
Function: More accurately controls the refrigerant cycle, optimizes energy efficiency, and provides additional protection.
3. Summary Table
Sensor Name Installation Location Main Function Possible Failure Symptoms
Indoor Environment Sensor Indoor Unit Air Inlet Detects room temperature, controls start/stop No cooling/heating, does not stop, frequent starts/stops
Indoor Pipe Temperature Sensor Surface of Indoor Evaporator Freeze protection, cold wind prevention, defrosting Freezing during cooling, no heating, no defrosting
Outdoor Condenser Sensor Surface of Outdoor Condenser Defrost judgment, overload protection Defrost logic error
Outdoor Environment Sensor Outdoor Unit Air Inlet Monitors external temperature, limits operation Performance limited in extreme weather
Compressor Discharge Sensor Compressor Discharge Pipe Prevents compressor overheating damage High-pressure fault, frequent protective shutdowns
Compressor Suction Sensor Compressor Suction Pipe Optimizes system cycle, protects compressor (less common)
Friendly Reminder:
The resistance of these sensors changes with temperature, and during maintenance, their resistance values at different temperatures are usually measured to determine their condition. Different brands and models of air conditioners may have slightly different numbers and configurations of sensors (for example, some low-end models may omit certain outdoor sensors), but the indoor environment and indoor pipe temperature sensors are absolutely essential. All these sensors are NTC thermistors.