jbaj007 offers very sound advice. It is very important that you study and know full well what you are doing. If you try to charge through the high side, you can blow up a refrigerant can in your face.
There are several really good manuals available through aircondition.com. There is also a link there to ackits.com. They have an excellent manual, I think from master cool.
Study up, be safe and enjoy fixing it yourself.