An AC thermistor is a type of temperature sensor that is commonly found on modern AC systems. They detect temperatures and send a resistance signal to the AC control module so that the automatic adjustments can be made to keep the cabin at the correct temperature. As they are basically ambient temperature sensors, they can be found both inside the cabin and underneath the hood of a vehicle.

AC thermistors read and interpret data on temperature that is critical to the proper operation of a computer controlled AC system, such as those found on most modern vehicles. When the thermistors fail or begin to have problems, they can negatively affect the performance of the entire system and should be inspected. Usually, when an AC thermistor has failed, they will produce a few symptoms that can alert the driver that there is a problem.

Limited cooling

One of the first signs that an AC thermistor may be having a problem is that the AC will only blow cold air for a limited amount of time. If an AC thermistor is not operating properly, it cannot alert the computer of the cabin temperature. Therefore, the module will not be able to activate or deactivate the AC so that the correct temperature can be achieved. This may cause the AC to blow cold air in short bursts, or only for a limited amount of time.

The blower will not function properly

Another symptom of issues with a thermistor will be problems with the blower. Some blower motors use the signal from the thermistor to control their operation. If a thermistor is giving improper, weak, or inconsistent signal, then the blower motor operation may be weak, erratic, or may not function at all. As the blower is what blows the air from the vents, any problems with the blower, caused by the thermistor or not, will greatly affect the AC system’s ability to cool the cabin.

Because AC thermistors can play such a critical role in the proper operation of an AC system, if you suspect that you may have a problem with it, have the AC system diagnosed by a professional technician, such as one from YourMechanic. If needed, they will be able to replace the AC thermistor and restore full functionality and operation to your AC system.

This article originally appeared on as Symptoms of a Bad or Failing AC Thermistor and was authored by Eduardo Ruelas.

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