ok It looks like the Model
AF40-NO4-Z - is Correct and the
AFM40-NO4-Z - is the reverse one.
The model number can be found on the side of the filter.
http://www.landisusa.com/filter9.JPG
And correct to fix it all you do is spin it around so the arrow on top faces reverse. and your line comming from the compressor goes into the OUT port.