If your air conditioner is freezing up, you should turn off the system and allow it to thaw completely before attempting any repairs. Once the system is thawed, you can check the air filter and clean or replace it if necessary. If the refrigerant levels are low, you should call a professional HVAC technician to locate and repair the leak and recharge the refrigerant. It's also a good idea to have your air conditioner serviced regularly to prevent future problems.