If all the R134 is gone, you cannot just simply add refrigerant. You must first evacuate the system with a vacuum pump. Any trapped air in the system means you have water as well. The water will freeze in the lines when you operate the A/C unless it is purged.
My advice - find someone who is knowledgeable with A/C, has a vacuum pump and the proper gauges, and have them show you what to do.
