You also said your system has not been used for at least 2 years and it would not be unreasonable that rubber O rings would be dried out and leaks would occur from those. This is an inexpensive fix and I would recommend replacing these BEFORE charging the system with anything. These are not expensive, but you would have to remove any hoses connected to parts of the system to get to them. They are not hard to replace, but it could be a little time consuming and the effort is well worth it. There is a very good chance that if the system has not worked for awhile, it's because it won't hold refrigerant without leaking from somewhere.