If there is no pressure at all that means you have a BAD leak. The good news is you have no refrigerant to recover. Try the other valve under the silver cover. If nothing comes out you have no refrigerant left. That is a good news / bad news thing. The good news is no recovery is needed. The bad news is you have a major leak. Your receiver / dryer is toast. If you plan to replace all the hoses now is the time. You should flush any condenser you plan to keep. Now is the time to upgrade the system "while you are in there"
What the heck it is only money.