In good repair the AC works great. You have two problems that need to be addressed:
1. Leaking refrigerant- The dye will point to the problem and you can fix it.
2. Foam from vents means failed mix flaps. Hot air is mixing with cold so your AC efficiency is poor. There is an online pdf how to fix this without spending a wad of money.
http://986forum.com/forums/performance-technical-chat/25401-foam-shooting-out-ac-vents.html
These two repairs should restore your AC to good working condition.
