The filters on the following page are for the Culligan Aqua-Cleer Reverse Osmosis System:
http://www.waterfilters.net/culligan/reverse-osmosis/Culligan-AC15.htm
These are the filters you will need for your system. The 4th filter is a post filter that is installed after the 3 housings in the system.
Thank you,
WaterFilters.NET