have a 98 Trans Am and the A/c Has started going warm. Went and got the R134a recharge kit from autozone and the can was barely getting cold... but the A/C was getting a bit cooler ... car ran for about 15 minutes and can wasnt even half empty... does it mean there is too much freon in the car already or should I just be more paitent and let it run longer cycling the A/C on and off??

help this A/C newb
Thanks