Getting it regassed first could get it working again. Aircon systems do lose refrigerant over time. If it initially works but then stops working, you're likely to have a leak somewhere, the condenser is prone - being at the front it's exposed to stones.

A decent aircon specialist will be able to do a diagnosis.

If this is the first of the new shape Focus models ,then I would strongly suspect that the a/c condensor rad has a leak.Very common on these early cars.hth

As this is a mk 1 model ,then it could be a different problem.Get it checked by an independent a/c specialist.Could be normal gas loss through age of vehicle.hth