2004 BMW Z4

Air conditioning work should be carried out by a qualified technician with the proper tools and equipment. Having said that, evacuate the system and recover the refrigerant, remove the compressor (it really helps to have the car on a lift) replace the receiver drier, add the correct amount of oil to the system and recharge the system with the appropriate amount of R-134a refrigerant. The work is quite straightforward, if you need these steps broken down, you might want to consider that you do not have the skill sets to perform this task.