I have an intermittent functioning of the Air conditioner, it starts with good cooling then compressor does not work properly and temperature rises up to 25C without the compressor functions
Then you need a good AC specialist to take a look at it. This is not a diy repair. It may be low on refrigerent but it is better to get a true diagnosis.
The car is 12 years old so a low refrigerant charge is not out of the question. Agreed with Mustangman about an A/C specialist.