Automotive AC – Temperature Sensors

Temperature sensors are used in the AC system to sense temperature and prevent the evaporator from getting too cold and freezing up. These sensors are just thermistors that operate by varying resistance as the temperature rises and falls. The module that controls the HVAC sends a reference voltage to these devices and continually monitors the voltage drop across it as the temperature changes. These sensors can be tested by testing the voltage drop across the sensor with a digital multimeter (DMM) or by using a scan tool and monitoring the sensor input in the data list.

Other types of temperature sensors that are used in the AC system include the ambient air temperature sensor, the cabin temperature sensor, and the coolant temperature sensor. These variable sensors are used to sense temperature in their given location to allow the AC system to operate as designed in a reliable manner.

The evaporator temperature sensor is located in the duct box very near the evaporator core. Care should be taken when installing the new sensor to prevent damaging the evaporator

The ambient temperature sensor is typically located at the front side of the vehicle either to the left or right side of the radiator and condenser. It must be a reasonable distance away from heat sources so it can accurately measure the outside temperature, which is used for the fuel injection system as well as for the HVAC

The engine coolant temperature sensor is located at some point on the engine that is exposed to engine coolant. This sensor is located at the rear of one of the cylinder

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