The access is under the dash, behind the glove box. You have to remove a couple of screws and lower the panel and then you can see the access to the cabin filter and the air conditioning motor. Slide the two whitish latches on each and the covers come off giving you access. Pull the cabin filter out and replace. You can get the part number off the filter or do a search for Crossfire or 2004 SLK320/32 cabin filter.....