2 Stage Twist-Locks Replacement

Confused on which cartridge on which side when replacing the cartridges?

(if you are looking at the back of the header):

PW-QC-C2 (AC750) is on the left side which is the side where outlet is
PW-QC-P1 (AC200) on the right side or the side where the inlet is 2-Stage-Twist-Locks-Replacement 2  2-Stage-Twist-Locks-Replacement 3  2-Stage-Twist-Locks-Replacement 1