DON'T USE FREEZE 12 or any of the other junk refrigerants. If you refuse to use R12 as it was designed, then use R134a.

It is a really bad thing that the system was open for a year. The BEST thing to do would be to thoroughly flush all lines, put the compressor back in place and flush it with a little Mineral oil and the pump out as much as you can get. Mount the compressor and then vacuum check. If it will hold a vacuum for an hour or two, then replace the filter/dryer, distribute 8 oz. of mineral oil around the system, evacuate and charge with R12.

If you STILL insist on staying with R134a, the process is exactly the same since the system has been open for a year. The only difference is that the 8 ounces of oil should be Ester oil and of course the different refrigerant.

ALL of the junk refrigerants fall into one of two categories. They are either a blend or flammable. I hope I don't have to explain why a flammable is a bad thing. The blends have multiple components that leak at different rates. Once you have a leak, the only way to get the blend correct again is to completely empty the system (illegal without recycle equipment specifically for that particular junk refrigerant) and then evacuate and recharge.

Also it is illegal to charge with ANY alternative refrigerant without labeling and using the appropriate fittings.