Apple Hardware Test - How to test fan?

Check the fan cable to make sure it was not damaged. Also check the pins on the cable connector and also the connector on the Logic Board. It is easy to damage them when disconnecting the cable from the Logic Board. It could be as easy as reseating the cable to the Logic Board.

Sometimes those fan connectors can be difficult to remove and will pull or lift the connector from the Logic Board if you are not careful. Sometimes the wire/pin can pull from the cable connector or the wire can become pinched causing a break in the cable.

Sometimes the fan connector won't fit properly when reinserting it into the Logic Board connector and it just needs to be reseated.

Did you remember to reconnect the small cable connector next to the power supply connector? This second cable is the same style as the fan connector. It is just to the left of the power supply cable when the Mini is positioned with the power supply on the right.

Use Macs Fan Control to check the fan speed and system temperature sensors.

Ok, I wasn't sure since a lot of times it is necessary to pull the Logic Board forward when replacing a drive.

Have you tried the SMC reset & PRAM reset?

Your only option is to try another fan to determine if the problem is the original fan or the Logic Board.

In fairness to ifixit, their repair guides are just a wiki community effort. Anything and everything provider there comes with no guarantees or promises at all, either stated nor implied. That’s the way the wiki commons community license is written. OWC is similar - they provide information which you chose to use at your own discretion, but they offer no guarantees of success since they have no idea of, nor any control over the skill level of the people who use their information content.

Any small mulitwire, thinwire connector is inherently somewhat fragile when handled. Quite honestly, just about everything in such a small form factor like a Mac Mini is somewhat fragile when being disassembled or reassembled.

if you can visually confirm the fan is not turning, and the cable and it’s connector themselves seem intact and fine, then it may be a bent or loose pin on the logic board connector. Without knowing the pin layout on the fan cable, I don’t know how to power it and check it outside of the device, but if you can find info on that, try it to confirm the fan itself is not the issue.

Everything is delicate to some extent. While most times there are no problems, other times those connectors can be very tight the first time you go to disconnect the cable.

As I mentioned previously, try another fan. If it works then problem solved, otherwise the only other thing it can be is the Logic Board.

There is a chance the fan is running, but it is not reporting its speed. Power on the mini without the bottom cover to see if the fan is spinning.