I wouldn't buy any high dollar or difficult to replace parts without recharging and leak testing. You probably have a minor leak. You can pull sufficient vacuum using a good air compressor and one of these:

http://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html

To introduce refrigerant with dye into the system, you will want a manifold like this:

http://www.harborfreight.com/AC-R134A-Manifold-Gauge-Set-60806.html

You are supposed to introduce a certain mass of refrigerant and see certain pressures on the high and low side (shown in the manual). If you let the system run for a while, you can use a blacklight to look for dye to have leaked out. I used those parts several years ago and it actually worked very well. The pressures shown will tell you if your compressor or other parts need replacement. You will also want an infrared thermometer to zap various components in the system. If you don't have a manual, I could look up the pages in the manual and post it.

Corbin
'97 GSX dressed like a '95 ESi