As of now, Air conditioner uses R22 refrigerant. In coming days ACs will come with refrigerants such as R410A, R407C etc.
it depends on the gas you are using. for ex\mple r134a and r22 you charge vapour through the low side and some gases are liquis charge only r404a r409 r407c and others these you charge carefully and slowly as liquid through the low side.