I would start with one of those Do-it-yourself AC repair kits. The type with a bottle of refrigerant, gauge and hose that you can get for ~$20-30. Start by using it to check your coolant level and then add coolant if it needs it. If the system has a leak, then keeping the coolant level up will help a lot.
example:
[ame]http://www.amazon.com/SubZero-Synthetic-Booster-Reusable-Recharge/dp/B0002KKLJS/ref=sr_1_4?ie=UTF8&qid=1345117232&sr=8-4&keywords=ac+refill+kit[/ame]
Then I would keep an eye on the coolant level for a few weeks/months. If it keeps falling on you, requiring you to top it off, then you know you have a leak somewhere and then you can start shopping around for AC mechanics in your area.
example:
[ame]http://www.amazon.com/SubZero-Synthetic-Booster-Reusable-Recharge/dp/B0002KKLJS/ref=sr_1_4?ie=UTF8&qid=1345117232&sr=8-4&keywords=ac+refill+kit[/ame]
Then I would keep an eye on the coolant level for a few weeks/months. If it keeps falling on you, requiring you to top it off, then you know you have a leak somewhere and then you can start shopping around for AC mechanics in your area.