Using your right hand, wiggle, tug, and pull the entire fan assembly out
of the computer. It attaches to the logic board via a connector that you
don’t need to worry about disconnecting, it’s a pressure fit.
Remove the Phillips screw from the base of the fan assembly, located at
the bottom left of the processor heatsinks.
OWC Multi-Mount
Chapter 3 - Mac Pro 800MHz Disassembly
3 MAC PRO 800MHZ DISASSEMBLY