HP Apollo 4200 Gen9 User Manual page 108

Install the fan in fan bay 5.
b.
To enable fan redundancy in a dual-processor configuration, all 10 fan bays should be populated.
16.
Obtain a Redundant Fan Option Kit (PN 806562-B21) and install five more fans in fan bays 6–10:
Remove the fan cage cover.
a.
Hardware options installation 108