Golf mk5 A/C not working properly...Help!!!

Hi
I have a Golf v 2.0 SDI. I first noticed during the winter months that the outside temperature reading on the dash stopped working properly. The temperature would plummet to something silly like -30degC. It was an intermittent fault and seemed to right itself when it felt like it. Now the weather is getting warmer and the A/C is needed I have noticed that this seems to be linked to the air con. When the outside temperature sensor is reading sensible values the air con kicks out cold air. However, when it starts to plummet into minus figures the air con ceases to work.
Questions...
1. Are the outside temp sensor and the a/c linked? (or am I talking rubbish?!!)
2. If I replace the sensor will it fix my problem?
3. Where is the sensor?!
....or is it something else?!

Please help....it's getting hot out there!!

Thanks