The reasons why the fan is ‘turned over’ should become obvious when the airflow is considered.
PSU = Power Supply Unit.

TC internal fan mods
The ‘standard’ as-manufactured set up shown on the left. The air would be drawn in from the side opening.
(Shown with “Air in” helpfully written on the picture) In this position it would blow onto the side of a piece of the edge of the hard drive.
(Shown with arrows going upwards, badly drawn by me).

There are THREE fundamental errors with this positioning, one of which cannot be seen and must be explained.

1. THERE IS NO OPENING IN THE BASEPLATE TO ALLOW AIR IN. The fan is normally mounted to the aluminium baseplate, on three small rubber legs.

2. The fan creates a pressure difference to make air flow from low pressure (air input) to high pressure (air outlet). The sponge gasket (shown on the fan fitted to the aluminium baseplate) is an EXACT FIT to the opening of the plastic cover on the PSU (shown daubed with yellow ‘Kapton’ tape). As supplied, THE FAN DOES NOT BLOW THROUGH THE PSU, although it seems obvious to me that it was intended so to do.

3. You cannot see this bit. THE FAN (with the TC powered up and working) IS NOT TURNED ON.

Sorry for the shouting, but these are fundamental design errors; without correction they persist in brand-new units. (Mostly).

These other pictures may help with understanding, why I do what I do!

TC fan mods details
A ‘converted fan’. The opening at the top has tape over it, but I blank off the sticky bit that would face the inside of the fan.
It would pick up dust and bits, which would impede the airflow.
The whole fan conversion takes ages to do correctly (as shown in ‘The Process’) but is VERY effective when completed and installed.

TC fan plug & socket
This will help to work out what to chop and what not.

TC external view fan mod
My own early prototype conversion unit, shamelessly flashing its screw heads to the world!
The airflow is shown.

The unaltered case has dozens of small oval holes around the aluminium edge, which are hidden from view by the lip of the rubber base mat. It impedes the airflow hardly at all BUT ONLY WHEN THE FAN IS WORKING.

An unaltered case will give VERY SLIGHT natural convection, if placed on its edge like above BUT WITH THE FAN AT THE LOWER EDGE.
The air will naturally rise through the PSU and effect some slight cooling.

This is the covering note that goes back with the modified TCs.

TC return note + ZTL logo