Poor airflow (dirty evaporator coil) or dirty air filter. Blower motor not on correct speed or not going full speed. blower wheel packed with dirt. Insufficient return. Low refrigerant charge. If you had to have refrigerant added, good chance (as long as it was not misdiagnosed as low refrigerant instead of a plugged evaporator coil etc.) you have a leak. There is no way to tell how big the leak is unless you start needing recharged 2 or more times a summer then it is time to find the leak and fix/replace the leaking component.