is the temperature HOT? or just not cool? does moving the slector hot/cold change the temperature? (is the temperature control on the head unit broken?)

Does the air flow change locations when you select vent/floor/defrost etc? (Is the vent selector broken?)

how long had the A/C been on before you decided it wasnt getting cool? on really hot days, it can take my truck a few minutes of driving to start to cool well.

Can you have your pressure checked? If all of the above is working, and the compressor is clicking on, then the only thing left I can think of is either the freon is low, or something is broken and its not pressurizing the system.

Run the A/C for a while, and you should notice condensation develop on one of the A/C lines under the hood. thats a good sign, things are working.

However, if no condensation, or has low pressure, or all else fails:
You could pour some more freon in, but if it leaked out once, chances are its gonna leak out again. May need to have it serviced if you cant find the leak.