HP L28712-001 CPU cooling fan is the processor-side replacement fan listed for the HP ZBook 15 G5. It is identified separately from the graphics-board fan, part L28713-001, helping distinguish the two cooling components in this workstation.
The service guide describes the fan as an assembly connected to the system board by a fan cable and secured with two captive Phillips screws. This part is for the processor area; the separate graphics fan has a different spare part number.