Suck on the system like the other say before you take it apart. If you want a good solid system replace the compressor, expansion valve and receiver drier and drive belts. Also, the high pressure hose, or smaller hose that runs closer to the exhaust manifold is a common leaker so you might want to replace that too. You might want to pick up some compressor bushings, alt bushings and power steering bushings while your at it. I think you need 10 bushings and they should be the same, not sure on 89. Sounds like a lot but it really is worth it so you don't have to mess around with it for a long time and your pulleys will be quiet! Put a vacuum on the system of 30in for 1/2 hour and see if it holds before proceeding. After you charge it leak test it, then leak test it again and do a visual after a few days. Some people like to use refrigerant dye and an ultraviolet light. R-12 is really the best, but it is expensive and hard to get. I personally use freeze 12, which I know is not the best, but I did get 45 degrees out of the center vents on warm day cruising down the freeway and it is cheap. Most people on this forum seem to prefer R-134A. I also move the a/c access ports up on the high pressure and low pressure lines for easy hook up. Use ester oil with r134a and mineral oil with R-12 and put some refrigerant oil on your line orings.