Usually used with Automatic Temperature Control (ATC), there are typically three sensors that sense temperature. One sensor is located on the outside of the car to sense outside air temperature. A second sensor is located in the interior to monitor temperature inside the car. The third sensor is usually located in the HVAC ducting, to sense delivered air temperature.
The system uses information from the sensors to make decisions on output commands to the HVAC system and the blower motor.
Problems with the HVAC sensors may result in poor regulation of cooling and heating. It is also possible that the speed of the blower motor will not change speed according to system demands. Regardless of the symptom, have it diagnosed as soon as possible by a professional technician.