My 1995 C280 is equipped with a refrigerant sight glass on the accumulator which shows cloudiness, indicating low refrigerant. Although it is still cooling it probably needs refrigerant added. Is it a good idea to recharge using the sight glass as an indicator so that it again is clear when compressor is operating or should you charge using a set of gauges? Also, it appears that charging port is on drivers side of engine below and to the left of the accumulator. Is this correct or is charging port located elsewhere.