Dash A/C issue

Does your service line have a gauge? If not find one. The last one I bought was at Ollies for like, ten bucks. I have a full manifold gauge set but, just find it quicker and easier to use the cheap low side hose and a can of refrigerant. If the system is out you have a pretty serious leak and the system is contaminated. You need to get the leak fixed and have it drawn down before adding refrigerant. If it still has some pressure you can charge it but, if it were mine I would add some stop leak. Don't even bother with the cheap stuff. It won't work. Get the good stuff, like $30.00 a can. Then service it up to a proper pressure, obviously with the compressor running. I put that stop leak in an old Volvo years ago and it worked till I sold it and never leaked down.