An AC can freeze due to a variety of reasons, the most common being a dirty filter, dirty coil, or low refrigerant. The thing to check is your air filter. A dirty air filter will restrict air moving across the evaporator coil and cause ice to form. Ice forming on the air conditioning unit puts high stress on the blower motor, compressor, and other parts of the unit. If this condition is not addressed immediately the result can lead to motor failure, compressor failure, damage to home, refrigerant leaks, and/or bigger refrigerant leaks. If the air filter is clean, a qualified technician will have to troubleshoot the system.