a/c not blowing cold on 1990 Jaguar XJ6

A/C blows, but not cold How much would it cost to repair

Asked by for the 1990 Jaguar XJ6
Too many unknowns at this point. If system is empty then will not blow cold. If is full but has problems turning on compressor then will blow hot. Many components effect the operation of a/c system. Have a qualified shop check it out.