To replace the automotive A/C Compressor, start by having the refrigerant discharged by a technician. Then, remove the under-vehicle splash shield and raise the front of the vehicle on jackstands. Take off the accessory drive belt and remove the left front wheel. Disconnect the electrical connector and refrigerant lines. Remove the mounting nuts and unbolt the compressor. If installing a new compressor, follow the instructions for adding the proper amount of oil. For installation, replace any O-rings with new ones and lubricate them with refrigerant oil. Finally, have the system evacuated, recharged, and leak tested by a professional.