It's past six months and you can't prove that the condenser was faulty when you bought the car. It could simply have failed because it was hit by a stone during your possession of the car, or it could have failed due to lack of use of the air con. Air con needs to be run every week if possible because its lubricants are suspended in the refrigerant and without them being pumped around the system, the system can fail. See: www.honestjohn.co.uk/faq/air-conditioning/