The first thing you would want to do is check for leaks, the most common areas to check for leaks is where the aluminum lines are crimped onto the rubber hose on the low-pressure a/c line. This is the line that runs along the top front edge of your engine, if it's leaking it will be wet and greasy looking. If it's not leaking and you have verified the system has the correct amount of freon in it, then you can try cleaning your condenser and evaporator core. Here's a few videos for you to watch on the subject, there's also links in the video description for what you would need to clean your condenser and evaporator core.
Chris.