Refrigerant does not normally disappear from a closed AC system. If the refrigerant is low, there may be a leak or another issue that should be inspected before more refrigerant is added.
Weak cooling does not always mean the system needs a recharge. Airflow restrictions, dirty coils, electrical trouble, and control issues can cause similar symptoms. Adding refrigerant without checking the cause may not solve the problem.
A technician can inspect the system, explain whether refrigerant levels appear to be part of the issue, and review options before you approve any recharge or repair work. Learn more about refrigerant recharge.