sir,new compreesor fix new reciver drier fix cooling is front and rear is ok.but on 2003 Mercedes-Benz S500 4MATIC

when i start blower then compressor is on.and ac switch(on off)is off.what reasons.pls help me.

Most vehicles when set to any defroster position will also run the A/C compressor to help cool and condense moisture in the air before heating the air and blowing on your windshield (if air heated was not dry your windshield would fog up)