Dell OptiPlex 9020 All In One (Mid 2013) - Manual (Page 25)

4. Remove the screws that secure the power-supply fan to the chassis and lift it away from the computer.
Installing the Power-Supply Fan
1. Place the power-supply fan on the computer and tighten the screws to secure it to the chassis.
2. Align and place the fan duct from the computer.
3. Tighten the screw that secures the fan duct to the chassis.
4. Install:
a) system-board shield
b) VESA mount bracket
c) back cover
d) VESA stand
5. Follow the procedures in After Working Inside Your Computer .
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