Dell Vostro 220s (Late 2008) - Manual (Page 97)

Fan
97
Replacing the Chassis Fan
1 For the Vostro 220s:
a Lower the fan into the chassis such that the screw hole in the fan is
offset and slightly forward of the screw hole in the fan mount on the
chassis.
b Press the fan into the side of the chassis, and then slide it toward the
back of the computer until it sets against the stops.
c Proceed to step 3.
2 While holding the chassis fan in place, align the screw hole(s) and install
the screw(s) that secure the fan to the chassis.
3 Attach the fan cable to the system board (see "System Board Components"
on page 40).
4 Follow the procedure in "After Working on Your Computer" on page 45.