just to update on vulcanboy post..if a major leak then the receiver/dryer would also need replacing as well as the faulty component..this takes moisture out of refrigerant and the dryer can become saturated very quickly when exposed to excess levels of moisture during a major/fast leak..i have found that the system needs to be charged in order to locate a leak unless of course a previous dye application shows the leak..once leak found the refrigerant is then removed again,most garages i know of dont charge for this part of the service as they hope to benefit from the repair..
