The efficient operation of an air conditioning system relies on the synergy of key components. The temperature sensor, as the “sensing nerve” of the HVAC system, is the key to obtaining temperature data, which has a direct impact on indoor comfort, and also optimizes energy consumption and prolongs the life of the equipment. Its performance and reliability determine the overall performance of the air conditioning system.
What is An Air Conditioning Temperature Sensor?
The air conditioning temperature sensor is the core component that converts temperature into an electrical signal. By monitoring the temperature change of the ambient air or system refrigerant in real time, it transmits accurate data to the main control unit. With this mechanism, the air conditioner is able to achieve precise temperature control in cooling and heating modes, creating a consistently comfortable room temperature environment for the user.
In the heating, ventilation and air conditioning (HVAC) system, temperature sensors are mainly categorized into three types: thermistors, thermocouples and resistance temperature detectors (RTDs). The three are designed based on different physical principles, each adapted to different temperature measurement ranges, accuracy standards and application scenarios, from the daily temperature control of home air conditioning to industrial-grade precision environmental regulation, can provide reliable temperature monitoring solutions.
Classification of Air Conditioner Temperature Sensors
Thermistors
As the core element of temperature sensing for home air conditioners, thermistors are made of semiconductor materials through a special process, and their resistance values show unique nonlinear temperature response characteristics. Based on the temperature trend, thermistors can be categorized into two types: negative temperature coefficient (NTC) and positive temperature coefficient (PTC).
NTC thermistors play a central role in air conditioning temperature control by virtue of their negative temperature coefficient characteristics: by monitoring the indoor, evaporator and condenser temperatures, they provide data support for the temperature control system. Its fast response, high sensitivity, low cost and small size can accurately sense temperature changes and guarantee the efficient operation of air conditioners.
Thermocouple
The thermocouple works based on the “Seebeck effect” and consists of two different metal wires welded together to derive the temperature by measuring the thermoelectric potential generated by the temperature difference between the two ends.
It is resistant to high temperatures, has a wide temperature measurement range (-200℃~1300℃), simple structure and high mechanical strength, and is suitable for high temperature monitoring scenarios such as industrial air-conditioning, and is less commonly used in domestic air-conditioning.
Resistance Temperature Detectors
Resistance Temperature Detectors (RTDs) are wound with high purity metal wires and work by utilizing the property of linear change of metal resistance value with temperature. Compared with other sensors.
RTDs have high measurement accuracy, small error, and good linearity over a wide temperature range (-200℃~850℃), and are mostly used in systems with high temperature control requirements, such as high-precision central air conditioners. However, its high cost and slow response limit the application in ordinary household air conditioners.
Core Functions of Air Conditioning Temperature Sensors
Temperature Adjustment
Temperature sensors are like the “sensing nerves” of air conditioners, which accurately transmit indoor ambient temperature data to the temperature control center through real-time collection.
When the room temperature is monitored to be higher than the preset threshold, the cooling mode is triggered instantly; and when the actual temperature agrees with the set temperature, the compressor will be intelligently regulated to enter the energy-saving standby state. In heating mode, the sensor also uses dynamic monitoring as the basis for precisely controlling the start and stop of the heating components to ensure that the indoor temperature is always maintained in a comfortable zone.
Optimizing Energy Efficiency
With its excellent temperature sensing ability, the temperature sensor is able to effectively avoid ineffective operation of the air conditioner. When the temperature is close to the set value, the sensor will anticipate in advance and send instructions to the system, prompting the compressor to automatically reduce the operating frequency, thus significantly reducing energy consumption.
According to relevant data, air conditioning equipment equipped with high-precision temperature sensors, its energy efficiency can be increased by 10% to 20%, which is not only in line with the concept of green energy saving, but also brings intuitive savings in electricity costs.
Safety Protection
The temperature sensor shoulders the important responsibility of guarding the core components of the air conditioning system, and builds a solid line of defense for the safe operation of the equipment by continuously monitoring the temperature of key parts. When the evaporator temperature drops below the critical value, the sensor will immediately activate the protection mechanism to stop the refrigeration operation and avoid the occurrence of frost phenomenon.
If the condenser temperature is too high, the sensor will respond quickly by accelerating heat dissipation or temporary shutdown of the compressor and other measures to effectively reduce the risk of equipment failure, significantly extending the service life of the air conditioner.
Resistance Characteristics of Air Conditioning Temperature Sensor
Resistance and Temperature Correlation
In the air conditioning, the working principle of the temperature sensor and the thermistor, RTDs (RTDs) resistance changes are closely related. NTC thermistor is very interesting, the temperature rises, its resistance will follow the decline, and not a uniform decline, the decline in amplitude is sometimes large and sometimes small.
RTDs in the typical representative of Pt100, its resistance changes are more regular, the temperature is not uniform, the resistance changes are more regular, the resistance value is more regular, the resistance value is more regular, the resistance value is more regular, the resistance value is more regular, the resistance value is more regular, the resistance value is more regular. Pt100, a typical representative of RTDs, its resistance value changes more regularly, the temperature rises, the resistance value will rise uniformly.
The resistance of Pt100 is 100Ω at 0℃, and the resistance increases by 0.385Ω for every 1℃ thereafter, which is better than NTC thermistor in terms of temperature measurement accuracy. The resistance value of both changes with the temperature, and the air conditioning master control unit adjusts the operation state accordingly.
Impact of Resistance Characteristics on Air Conditioning Performance
The precision and response speed of the resistance value change directly affects the temperature control effect and regulation efficiency of air conditioners. Accuracy deviation will lead to data misjudgment: resistance value is high, even if the room temperature has reached the set temperature, the sensor still feedback high temperature, so that the compressor continues to run, resulting in excessive refrigeration and waste of energy.
A low resistance value will cause the air conditioner to shut down prematurely and fail to reach the set temperature. Thermistors, with their fast temperature response, allow air conditioners to adapt to fluctuations in room temperature in a timely manner, avoiding lag in temperature regulation, and thus have become a common sensor for home air conditioners.
Resistance Tolerance
Resistance tolerance refers to the allowable range of deviation between the actual resistance value of the sensor and the standard value, which is often expressed as a percentage (e.g. ±1%, ±2%).
The smaller the tolerance, the higher the measurement accuracy and the more precise the air conditioning temperature control. Data centers and other demanding temperature control scenarios, often use RTDs with a tolerance of <±0.5% to control temperature fluctuations within ±0.1℃.
Troubleshooting and Maintenance of Temperature Sensors
Common Types of Failures and Maintenance Methods
Deviation in Reading
When the air conditioner is in operation, there is often a significant deviation between the set temperature and the actual room temperature, e.g., if the temperature is set to 24℃, the actual measurement may reach 22℃ or 26℃. This abnormality is mostly caused by the sensor resistance calibration drift, poor wiring contact, or external electromagnetic interference and other factors.
When the resistance calibration drifts, use a professional instrument to recalibrate the resistance value; poor wiring contact, check the terminals, re-plugging and fixing, and replace oxidized or damaged connecting wires; external electromagnetic interference, install shielding devices to isolate the source of interference.
Sensor Damage
When the sensor has a complete failure malfunction, its resistance value will remain constant or completely lose the ability to respond. This abnormality will cut off the air conditioner’s temperature sensing channel, which in turn triggers a series of chain reactions, such as the compressor continues to run at high loads, or completely unable to start and other serious problems.
Common causes of this malfunction include deterioration of the sensor’s internal components, short circuits or broken circuits.After confirming that the sensor is damaged, it is necessary to replace the same type of temperature sensor, after the replacement of the temperature test and system debugging, to ensure that the sensor signal is transmitted properly.
Faulty Wiring
Broken, oxidized or loose connecting wires lead to abnormal transmission of resistance signals, causing the air conditioner to experience abnormal operation such as “fluctuating temperature display” and “frequent start/stop”. The connecting wire is bent for a long time, oxidized by moisture or not fixed firmly during installation.
For broken connecting wire, need to cut off the damaged part to reconnect and do insulation treatment; if oxidization leads to poor contact, use sandpaper to polish the oxidized part and reconnect it; loose connecting wire needs to be re-tightened and fixed, and replaced with a new connecting wire if necessary .
Maintenance and Cleaning Guidelines
- Regular inspection and maintenance: It is recommended to carry out special inspection on the air conditioning temperature sensor every half a year, focusing on observing whether there is any accumulation of dust, oil adherence or frost on the surface of the sensing probe, and checking whether there is any loose or oxidized connecting wires and other poor contacts, and deal with the abnormality immediately when it is found.
- Standardized cleaning operation: for the sensing probe surface dust, oil, it is recommended to use a soft brush or dry cleaning cloth to wipe gently; in case of probe frost, you need to turn off the air-conditioning system, to be naturally defrosted and then cleaned, prohibited the use of sharp and hard objects to scrape or use water, chemical detergents for cleaning.
- Scientific replacement guidelines: household air conditioning temperature sensors used for more than 5 years, industrial air conditioning more than 3 years, if the temperature reading deviation occurs frequently, and can not return to normal after cleaning and maintenance, reinforcement of the wiring, should be replaced in a timely manner. In high-precision scenarios, the replacement should be calibrated and debugged by a professional to ensure that the resistance – temperature characteristic curve meets the operating standards.
Warning Signs for Repair/Replacement
When the air conditioner has the following conditions, it is most likely that the temperature sensor is faulty, and should be promptly investigated or contacted for professional repair:
- the cooling/heating effect of the air conditioner drops significantly, and the target temperature cannot be reached for a long time after setting the temperature;
- the indoor temperature fluctuations, cold and hot, and set the temperature deviation of more than ± 2 ℃;
- the thermostat display temperature and the actual temperature measured by a handheld thermometer is inconsistent (deviation of more than ± 1 ℃). 4. the air-conditioning compressor frequently start and stop (the temperature of the air-conditioning compressor);
- air-conditioning compressor start and stop frequently (more than 2 times per minute), or continue to run for more than 1 hour without stopping. 5. air-conditioning display fault code (most of the air-conditioning start and stop);
- air conditioning display fault code (most air conditioning brands of temperature sensor failure will correspond to the exclusive code, such as “E1” “E2”, you can refer to the product manual query).
Conclusion
Temperature sensor is the core component of the air conditioner, accurately guaranteeing the accuracy of temperature control, affecting the operation of the equipment, energy efficiency and safety. When the air conditioner temperature control is abnormal, hot and cold failure, you can prioritize the investigation of the sensor. Non-professionals should not disassemble the sensor privately, and should contact HVAC professionals for overhaul to prevent equipment damage.
As a professional HVAC controller manufacturer, corestar is mainly engaged in temperature controllers, EEV controllers, speed controllers, high-precision temperature sensors and other products, which can provide accurate, efficient and reliable core control solutions for air conditioning systems, and effectively improve the operating performance and energy saving effect of the equipment.
