Lenovo ThinkCentre 3231 Hardware Maintenance Manual page 124

4. The rear fan assembly is attached to the chassis by four rubber mounts.
Figure 31. Removing the rear fan assembly
5. Install the new rear fan assembly by aligning the new rubber mounts of the
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Hardware Maintenance Manual
Remove the rear fan assembly by breaking or cutting the rubber mounts and
gently pulling the rear fan assembly out of the chassis.
new rear fan assembly with the holes on the chassis and push the rubber
mounts through the holes.
Note: The new rear fan assembly you received will have four new rubber
mounts attached.