Aircon Thermistor Problem

Aircon Thermistor Sensor Repair & Replacement Cost

Updated - Sun, 15 Jun 2025

What is a thermistor in aircon?

A thermistor is a type of temperature sensor commonly used in air conditioning systems. It is a resistor whose resistance changes with temperature. The term "thermistor" is derived from the words "thermal" and "resistor".

In an air conditioning system, a thermistor is typically used to measure the temperature of the air. It is placed in the airflow path, usually near the evaporator coil or inside the air handler unit. As the temperature changes, the resistance of the thermistor also changes. This change in resistance is used to provide feedback to the air conditioning system's control circuitry, allowing it to regulate the cooling or heating process.

The thermistor's resistance is typically connected to a control board or controller, which interprets the resistance value and makes adjustments accordingly. For example, if the thermistor detects that the air temperature is too high, the controller may activate the compressor to cool the air. Conversely, if the air temperature is too low, the controller may reduce or stop the cooling operation.

By using a thermistor, air conditioning systems can accurately monitor and control the temperature, ensuring optimal comfort and energy efficiency.

Indoor Aircon Thermistor on the FCU (Fan Coil Unit)

The indoor aircon thermistor on the FCU refers to the thermistor sensor used within the Fan Coil Unit to measure the indoor air temperature. The thermistor is typically located inside the unit's housing, near the evaporator coil or in the airflow path.

The thermistor continuously measures the temperature of the air passing through the FCU. As the air temperature changes, the resistance of the thermistor changes accordingly. This resistance variation is then used by the FCU's control circuitry to adjust the cooling or heating process.

The control board or controller in the FCU receives the resistance value from the thermistor and interprets it to determine the appropriate action. If the air temperature is too high, the controller may activate the cooling process to lower the temperature. Conversely, if the air temperature is too low, the controller may activate the heating process to increase the temperature.

The indoor aircon thermistor plays a crucial role in maintaining a comfortable and controlled indoor environment by providing accurate temperature measurements to the FCU. It allows the air conditioning system to adjust its operation based on the desired temperature set by the user or the system's automated controls.

Where is the thermistor located?

When to replace or repair an Aircon PCB?

When determining whether to replace or repair an air conditioning thermistor, consider the following factors:

1. Accuracy and reliability

A thermistor's primary function is to measure temperature accurately. If the thermistor is consistently providing inaccurate readings or behaving erratically, it may need replacement rather than repair. A faulty thermistor can lead to improper temperature control and reduced system efficiency.

2. Physical damage

If the thermistor is physically damaged, such as a broken or bent probe or damaged wiring, it may be more practical to replace it. Repairing physical damage can be challenging and may not guarantee optimal performance.

3. Age and condition

Consider the age and overall condition of the thermistor. If it is relatively new and in good working condition aside from a minor issue, such as a loose connection or a damaged cable, repairing it may be a cost-effective option. However, if the thermistor is old or has a history of recurring problems, replacement could be a more reliable solution.

4. System performance and efficiency

A malfunctioning thermistor can negatively impact the air conditioning system's performance and energy efficiency. If the thermistor is hindering the system's ability to maintain accurate temperature control or causing frequent cycling on/off, it may be best to replace it to restore optimal operation.

5. Professional assessment

Consult with a qualified technician or contact the manufacturer or authorized service center to assess the specific issue with the thermistor. They can provide expert advice on whether repair or replacement is the most appropriate solution based on the situation.

technician replacing the aircon thermistor

Why you should never repair a faulty aircon Thermistor?

We always recommend to replace the damaged Thermistor instead of trying to repair it. Here are a few reasons:

1. Irreparable damage

If the thermistor is severely damaged or has undergone extensive wear and tear, it may not be feasible or cost-effective to repair it. In such cases, replacing the thermistor with a new one ensures reliable and accurate temperature sensing.

2. Compatibility and reliability

Thermistors come in different types, specifications, and sensitivities. If the existing thermistor is outdated or incompatible with the air conditioning system, replacing it with a new one that is designed for compatibility and reliability may be a better option.

3. Cost-effectiveness

Repairing a thermistor can sometimes be costly, especially if the required components or specialized repair services are expensive or hard to find. In such cases, replacing the faulty thermistor with a new one may be a more cost-effective choice.

4. Warranty Considerations

If the air conditioning system is still under warranty, replacing a faulty thermistor with a new one from the manufacturer or an authorized service center may be the recommended course of action to maintain warranty coverage.

5. Overall system performance

The thermistor plays a crucial role in temperature sensing and control within the air conditioning system. If a faulty thermistor is affecting the system's overall performance, reliability, or energy efficiency, replacing it can help restore optimal operation.

Aircon Thermistor Replacement Cost

Thermistor replacement can cost anywhere between $120 to $250 including the material, transport and technician labor cost.

The cost of replacing thermistor can vary based on several factors, such as the brand and model of the air conditioning unit, the complexity of the repair, and the cost of the replacement parts.