Refrigerant, freon, suva, isotron, or any other cooling medium does not wear out, does not need replaced, and does not need recharged, topped off, or otherwise adjusted, if the system was installed properly and sealed properly during installation.
Actually, it should NEVER need recharging. The unit is a closed loop system. There is a leak somewhere in the system. Look for oily residue on pipe joints and connections. The leak may be so small that it only needs recharging once a season, but I would have that repaired.