BMW Repair: BMW 2004 325Ci Temp sensor, internal humidity, air conditioner compressor

Question
I seem to have a problem with my temperature sensor.
When it rains hard, I start getting a beeping sound in the panel and the temperature goes from +50F to -40F... at this same time, the air conditioner compressor seems to shut off. Big problem when its raining and all windows are fogged due to the internal humidity.
1) Would this indicate a temperature sensor problem?
2) Where can I find the sensor in my car.
Thanks
Ed

Answer
It sounds like a bad ambient temp sensor which is located in the lower part of the bumper area.It may only be a loose connection as it works correctly occasionally.Most times it would read extreme values(-40) if the sensor was bad,but where it reads correctly it may just be loose.
About the a/c I would have the freon checked to make sure the system is properly charged.