My 'new' used car needed a re-gas as there was none in the system. No leaks were detected during the re-gassing. Where could the original gas have gone?
every car with aircon needs to have the system recharged every 2/3 years as the gas is an refrigerant and transfers the heat in to cold air and evaporates...
I'm afraid essex bloke's answer displays a complete misunderstanding of the way in which refrigeration works. As tabathazig and mr_pointment say, the only possible explanation is a leak, however small.
No you can't Space, the gas has not dissapeared, it has gone where all the other gas has gone.......into the ozone layer to join all the other gas from fridges so causing global warming. So there!
I have my air con refilled every couple of years, and last year the garage offered a service whereby the pipes were flushed through with disinfectants and freshened.It was like having a new car again .... luverly jubblie.