Yes, at minimum you will need a descent manifold pressure set. That being said. If you are in need of adding refrigerant. You will also need to seriously consider the real possibility that you have a leak in the system. Properely repairing a leak is much more involved, and requires many more specialized tools, and knowledge on how to do it. It took alot of reading and hands on for me to fully understand the process, so I urge you to do the same before attempting to service your AC system. Merely adding refrigerant without knowing how yours is opperating could lead to complete failure. Just price a new AC compressor. I almost fainted when I did. So, to answer one of your questions, yes it is DIY, but to do it properely is much more methodical than it looks.