Modern vehicles are equipped with sophisticated heating and air conditioning systems that are highly efficient in achieving and maintaining comfortable cabin temperatures for the passengers. They are able to do this by using a series of sensors that work together to activate and regulate the AC system. One of the primary sensors that plays a key role in the operation of the AC system is the ambient temperature sensor, also commonly known as the ambient temperature sensor switch.
Vehicles in hot or cold extremes will require significantly more effort from the HVAC system to both cool and heat the cabin of the vehicle. For this reason, it is important for the system to be aware of the temperature of the environment that the vehicle is in. It is the job of the ambient temperature sensor to measure the external temperature of the vehicle as a reference point for the computer to make calculations. The computer will continuously monitor the signal from the ambient temperature sensor and make automatic adjustments as needed to maintain cabin temperature. When the ambient temperature sensor fails, there will usually be a few symptoms that may alert the driver that a problem with the sensor has occurred and it should be inspected or replaced if needed.
1. The AC auto mode will not work
Most modern vehicles have an auto AC setting that will allow the vehicle to automatically set and regulate the temperature. The AC system will simply read the ambient and cabin temperature sensors data and continuously cycle the AC system on and off as required to keep the cabin cool. When the ambient temperature sensor fails, the system does not have a reference point from which to base it’s automatic calculations and the setting will not work.
2. Inconsistent cooling
Another symptom of a bad or failing ambient temperature sensor is inconsistent cooling. As the ambient temperature sensor plays a direct role in the automated function of the AC system, when it is having a problem this may interfere with the system’s ability to cool the vehicle. If the ambient temperature sensor fails or is sending out an inconsistent signal, then the AC system may have trouble maintaining cool and comfortable cabin temperatures.
3. Incorrect reading on temperature gauge
Another more obvious symptom of a bad or failing sensor is an incorrect reading on the vehicle’s temperature gauge. Most vehicles will have some sort of display somewhere on the interior of the vehicle that indicates the outside temperature of the vehicle, usually read by the ambient temperature sensor. If the reading on the gauge or indicator is off by more than a few degrees, then the sensor should be replaced, as the incorrect reading may interfere with proper AC system functions.
The ambient temperature sensor plays an important role in the overall operation of the AC system. For this reason, if you suspect that your ambient temperature sensor has failed, or is having a problem, have a professional technician, such as one from YourMechanic, inspect the AC system and replace the sensor if necessary.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Ambient Temperature Sensor (Switch) and was authored by Ed Ruelas.