The Purpose and Function of Thermistors in Aircon Systems

Is your air conditioner not cooling as it should? Thermistors play a crucial role in regulating the temperature of your aircon system. This article will guide you through their purpose, how they differ from thermostats, and what to do if they fail.

Stay cool and read on.

Understanding the Role of Thermistors in Air Conditioning Units

Thermistors serve as the temperature-sensing backbone of air conditioning units, constantly monitoring and adjusting to ensure optimal cooling efficiency. Positioned near the evaporator coils, these small but mighty components detect subtle changes in temperature by varying their electrical resistance.

This ability allows them to send precise signals to the unit’s control system, initiating necessary adjustments in cooling output to prevent overcooling or overheating. Utilising NTC thermistors, renowned for their rapid response to temperature fluctuations, aircon systems can achieve precise climate control within buildings.

Their role extends beyond merely measuring ambient temperatures; thermistors actively contribute to the longevity and reliability of heating and cooling systems. Providing critical data that helps maintain a consistent indoor environment prevents excessive wear on compressors and other crucial parts of the air conditioning unit.

This ensures your living or workspace remains comfortable and contributes significantly towards energy efficiency by regulating the system’s operation based on real-time temperature readings.

The Difference Between a Thermistor and a Thermostat

In air conditioning systems, the distinction between a thermistor and a thermostat is critical for effective temperature control and regulation. Here is a comparison in a tabular format:


Feature Thermistor Thermostat
Function Acts as a temperature sensor, changing resistance with temperature. Regulates the system’s temperature, acting as a control device.
Operation Exhibits a large change in resistance proportional to temperature change. Switches heating or cooling devices on or off to maintain desired temperature.
Component Type Solid-state temperature-sensing device, sensitive to temperature. Control device, not directly sensitive to temperature changes.
Applications in AC Systems Used for precise temperature sensing within the unit. Used to maintain the overall temperature of the environment.

This table highlights that thermistors and thermostats play complementary roles in air conditioning units, each essential for precise temperature control and regulation.

Identifying Symptoms and Consequences of a Faulty Thermistor

A faulty thermistor in an air conditioning unit can wreak havoc on its performance. Spotting the early signs of trouble helps prevent bigger issues down the line.


  • Incorrect temperature readings often signal a malfunctioning thermistor. The device may display temperatures significantly higher or lower than the room temperature.
  • Erratic or inconsistent temperature control becomes apparent when the AC fails to maintain a stable temperature. This fluctuation can cause discomfort and frustration during use.
  • Short bursts of cold air from the AC unit, rather than a continuous flow, indicate a faulty thermistor. This symptom disrupts the normal operation of the aircon, leading to inefficient cooling.
  • Increased energy consumption might occur as the aircon struggles to reach desired temperatures due to incorrect readings from a damaged thermistor.
  • The air conditioner may frequently turn on and off without reaching the set temperature, another indication of thermistor failure.
  • Over time, consistent exposure to incorrect temperatures can strain other HVAC system components, including compressors and fans, potentially leading to premature failure.

Essential Maintenance Tips: Replacing and Testing Your AC’s Thermistor

Keeping your air conditioner’s thermistor in top condition ensures efficient cooling. Regular checks and maintenance help prevent cooling issues and system failures. Here are essential tips for replacing and testing your AC’s thermistor:

  1. Identify the symptoms of a faulty thermistor, such as inconsistent cooling or frequent cycling of the aircon unit. These signs indicate it’s time to test or replace the component.
  2. Turn off the power supply to your aircon system before attempting any maintenance work. This ensures safety from electric shock and prevents damage to the system.
  3. Locate the thermistor near the evaporator coil or in the air handler of your air conditioning unit. Refer to the user manual if you’re unsure where it is.
  4. A digital multimeter set measures resistance (Ohms) and tests the thermistor’s functionality. A functioning thermistor will show resistance changes correlating with room temperature changes.
  5. Compare the readings from your multimeter with standard values provided by your AC manufacturer to determine if the thermistor is working correctly.
  6. Remove a malfunctioning thermistor by disconnecting its wiring connectors and unscrewing it from its mounting position. Handle this task gently to avoid damaging surrounding components.
  7. Install a new thermistor by reversing the removal process, ensuring correct positioning and secure connections.
  8. Apply corrosion-resistant coatings around connections if your model requires it, providing extra protection against wear and tear caused by humidity and temperature fluctuations.
  9. Test the newly installed thermistor using a digital multimeter again, verifying correct operation before turning on the whole system.
  10. Finally, switch on your air conditioning unit to confirm that it cools efficiently, paying close attention during its initial cycles for any irregularities in performance.

Introduction to Aircon Printed Circuit Boards

Aircon printed circuit boards (PCBs) serve as the nerve centre of air conditioning systems, automating crucial processes such as temperature adjustment, flow rate management, and humidity control.

These components rely on a sophisticated network of signals to ensure your HVAC system operates smoothly and efficiently. Constructed from insulating materials like fibreglass or composite epoxy, aircon PCBs provide a sturdy foundation that supports various electronic components, including capacitors and relays.

This design allows them to communicate commands and collect data seamlessly across the air conditioner’s parts, ensuring optimal performance.

The role of an air conditioner PCB extends beyond simple command relay; it plays a pivotal part in the functionality of the entire unit. It interprets signals from temperature sensors such as thermistors and inputs from the user interface to maintain desired environmental conditions within a space.

Additionally, these boards manage operations of essential elements like fans, compressors, and thermo-electric coolers by regulating the power supply and preventing potential overloads or failures through efficient conductivity pathways.

The integration of PCB technology in aircon signifies advancements in precision cooling technologies capable of mirroring exact user specifications for comfort levels while providing energy-efficient solutions for modern living spaces.


Thermistors are pivotal in ensuring our air conditioning units function at their best. They precisely measure and regulate temperatures, keeping environments comfortably cool.

By responding to even slight changes in temperature, these components help maintain optimal cooling efficiency. Understanding their operation and importance highlights the need for regular maintenance checks.

This ensures our cooling systems remain reliable and efficient throughout their lifespan.

Explore our beginner’s guide to aircon printed circuit boards for a more in-depth understanding of how thermistors interact with other components.


1. What is a thermistor in an aircon system?

A thermistor in an aircon system is a type of resistor that changes its resistance with temperature, helping to control the cooling process.

2. How do thermistors work in air conditioners?

Thermistors measure the ambient temperature around them and adjust the air conditioner’s cooling power accordingly, ensuring efficient heating or cooling.

3. What are PTC and NTC thermistors?

PTC (Positive Temperature Coefficient) thermistors increase their resistance when the temperature increases, while NTC (Negative Temperature Coefficient) thermistors decrease their resistance with rising temperatures.

4. Why are PTC thermistors important for HVAC systems?

PTC thermistors play a crucial role in HVAC systems by safeguarding against overheating and helping maintain optimal operating temperatures within components like fan heaters.

5. Can a thermistor replace a thermostat in an air conditioning system?

While both handle temperature control, thermostats switch heating or cooling devices on or off to maintain desired temps, whereas thermistors provide precise temperature readings for more accurate adjustments.

6. Are there different types of materials used for creating thermistor sensors?

Yes! Thermistor sensors can be made from various materials, including ceramics, polymers, and composite materials, designed to meet specific requirements such as resistance to corrosive substances or varying temperatures.


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