AC Sensors Explained: Types, Functions & How They Improve Performance

Published: 15 May 2025

Welcome! Are you tired of your air conditioner not cooling as it should or wasting too much energy? Have you ever wondered why your AC isn’t performing as efficiently as it should? It’s a common issue many face, and the problem often lies in not understanding the sensors controlling your AC.

But here’s the good news: Once you understand your AC’s different types of sensors, you can fix these issues and enjoy better performance. In this guide, I’ll walk you through each sensor in simple terms so that you can make the best decisions for your home. Let’s jump in and explore how the right sensors can make your AC work smarter and more efficiently!

Table of Content

How Do Sensors Work in Your AC?
Types Of Air Conditioner Sensors
Conclusion

How Do Sensors Work in Your AC?

The sensor in your AC plays a key role in keeping the temperature steady and maintaining the one you set. It regularly maintains the perfect climate by turning the compressor on and off smoothly. The sensor monitors the temperature, ensuring your AC runs efficiently and doesn’t waste energy.

So, the next time you feel that cool breeze, you can thank the sensor for making it all happen!

Types Of Air Conditioner Sensors

In air conditioners, different sensors are used to ensure smooth operation.

Non-Inverter ACs typically have 2 sensors, both located in the inner unit.
Inverter ACs use 5 sensors — 2 in the inner and 3 in the outer units.

These sensors come in two main types: PTC and NTC.

PTC Sensors have resistance that increases as the temperature rises and decreases when the temperature falls. They are directly proportional to the temperature.
NTC Sensors, on the other hand, work oppositely. When the temperature rises, their resistance decreases, and when the temperature drops, the resistance increases. They are inversely proportional to the temperature.

1- Room Temperature Sensor

The Room Temperature Sensor is responsible for maintaining the desired temperature in your room. It monitors the current room temperature and sends signals to the compressor to turn it on or off accordingly, ensuring the temperature stays at the set level.

Let’s say you set the temperature to 22°C and set a limit of 3°C. The sensor will keep track of the room’s temperature. Once the temperature rises to 25°C, the sensor will signal the compressor, turning it on to cool the room back to the desired level.

Where is the room temperature sensor located, and what does it look like?

The room temperature sensor is in the inner unit before the evaporator coil. It is separate from the coil and not directly attached to it. The sensor is black, and its head is made of plastic.

It senses the air coming from the blower, which helps it detect the room temperature. Based on this, the sensor sends a signal to the compressor to turn on, ensuring the temperature remains constant.

2- Evaporator Coil Sensor

The copper-headed Evaporator Coil Sensor is attached directly to the evaporator coil pipe. This sensor constantly monitors the temperature of the evaporator coil, which must remain at a specific level, not too cold or hot. Keeping track of the temperature helps ensure that the AC operates smoothly and efficiently.

Sometimes, ice can form on the evaporator coil, causing performance issues. When this happens, the sensor sends an immediate signal to the PCB (Printed Circuit Board), temporarily stopping the AC.

Ice formation can occur for several reasons, including a slow blower motor speed, poor airflow across the evaporator coil, dirt buildup in the pipe, or a dirty air filter.

If the evaporator coil is faulty, the AC will display an error code to alert you to the problem.

Does the Evaporator Coil Sensor work the same in both Inverter and Non-Inverter ACs?

The Evaporator Coil Sensor works similarly in both Inverter and Non-Inverter ACs.

3- Ambient Temperature Sensor

The ambient temperature sensor is in the outdoor unit near the condenser coil. Its primary job is to sense the temperature of the surrounding environment, specifically the outdoor temperature around the outer unit, and adjust the fan motor’s speed. This is important because the AC adjusts its operation based on the outdoor environment. If it’s hot outside, the sensor makes the AC work harder to cool the room. However, the sensor helps the AC use less energy if the weather is cooler.

Like the other sensors, the ambient temperature sensor has a durable plastic head, ensuring it can continue monitoring the outside temperature without any issues.

Imagine it’s the middle of a hot summer day, and the temperature outside reaches 35°C. As the heat increases, the ambient temperature sensor quietly does its job and notices the temperature rise. It sends a signal to the AC, prompting it to work harder to cool the room and keep you comfortable.

Now, picture the evening arriving, and the temperature outside begins to drop. The sensor notices the cooler air and gently adjusts the AC’s cooling, reducing its power to save energy while maintaining a pleasant indoor temperature.

4- Condenser Coil Sensor

The Condenser Coil Sensor works similarly to the evaporator coil sensor. It is directly attached to the condenser coil, like how the evaporator sensor is fixed.

Its main job is to monitor the temperature of the condenser coil, ensuring it doesn’t get too hot or too cold. If the coil’s temperature becomes unstable or deviates from its normal range, the sensor sends a signal to the PCB (Printed Circuit Board). Based on this signal, the PCB will stop the AC from working to prevent further issues and protect the system.

Imagine the fan motor, which is located near the condenser coil, isn’t working correctly. Because of this, the heat from the condenser coil can’t escape outside, causing the coil to overheat. The Condenser Coil Sensor detects this temperature increase and immediately sends a signal to the PCB (Printed Circuit Board). In response, the PCB will stop the AC from running and display an error code on the AC’s screen.

To fix this issue and get the AC running again, you must address the error by fixing the fan motor or solving the underlying problem. Once resolved, you can restart the AC.

5- Compressor Discharge Pipe Sensor

The Compressor Discharge Pipe Sensor is located on the discharge pipe, which can be seen above the rotary-type compressor in the outer unit. This sensor plays a key role in monitoring the temperature of the refrigerant as it exits the compressor.

Its main job is to check if the refrigerant leaving the compressor is becoming too hot or too cold. If the temperature rises or descends above the safe limit, the sensor sends a signal to the PCB (Printed Circuit Board), instructing it to stop the AC.

The AC’s display will also show an error code, alerting you to the problem.

Conclusion

I’ve given you a deep dive into the different sensors in your air conditioner. Each sensor, whether the Room Temperature Sensor, Evaporator Coil Sensor, Ambient Temperature Sensor, or Compressor Discharge Pipe Sensor, plays a vital role in enhancing your AC’s performance.

These sensors monitor temperatures, control the compressor, and improve energy efficiency. When these functions are working correctly, your AC runs smoothly, and if any issues arise, the sensors alert you with an error code. Understanding the role of these sensors is the key to keeping your AC running well.

Which sensors are used in Non-Inverter and Inverter ACs?

In both Inverter and Non-Inverter ACs, NTC sensors maintain the system’s efficiency.

What happens if any of the sensors in the AC stops working?

If any sensor in the AC fails, the system will stop working. In such cases, you must replace the faulty sensor so the AC can function correctly.