Water Separator

Check visually for insect nests in the water separator air inlet.
Check visually for cracks or flaws in the appearance.
Check visually for cracks or flaws in the hose.
Check that A and C are not clogged by blowing air into B with A , and then C plugged.

Fig 1: Checking Water Separator
Courtesy of NISSAN MOTOR CO., U.S.A.
In case of NG in items 2 - 4, replace the parts.
NOTE:
- Do not disassemble water separator.