iFixit

Locate the bottom right fan.

Unplug the fan's power cable from the upper rightmost corner of the motherboard (connection J45). If there is a video card in place, carefully pull the cable plug down between the back edge of the video card and the motherboard. Note, the photo shows the unplugged cable and the area it plugs into outlined in yellow. No video card is shown in this photo.

Locate the tabs on the fan unit.

While pushing in on the tabs, highlighted in yellow, pull the fan back towards the cooling unit.

After the latches are out, pull the fan out.

After removal of the bottom right fan the space should look like this.

Locate the Cooling Unit on the Apple G5.

Put the CPU case on its back with the opening facing up to make the next steps easier.

Unscrew 8 T10 screws from the cooling unit. G5 models with the large Fujikura heat sinks (not shown in picture) will have 8 2.5mm hex screws.

The screws are somewhat hidden, so they cannot be see in the picture.

To visualize the location of the screws look 3 steps ahead.

The screws will loosen but will not come out, they are designed to loosen the unit, but remain in place.

Pull the cooling/processing unit straight up to prevent damage to logic board

This will require some effort and should be done with caution to avoid damage.

The sleeves around the 6 screws may hold it in, if so just take a pair of needle nose pliers and gently squeeze the sleeves until it releases.

Pull the bottom, then side towards the bottom of the CPU case, first to move around the bottom coolant sleeve around the heat sinking bracket. *heat sinking bracket not in picture*