Son has just passed his test last week, had his car two years mind you (thanks Covid) but yesterday it popped up that temp was too high. Went and checked and all seemed fine until I put the AC on and the fan didn't kick in.

Checked the fuses and the 40amp cooling fan fuse had blown, some time ago by the look of it! Anyway, changed out fuse, fine, until the AC kicks in, blows the fuse straight away but can hear the AC compressor running. My guess is the fan motor is goosed? Or is there any thing else I should be looking at. He's off in the car with a new fuse and told not to put the AC on, if the fan kicks in or tries to it will blow the fuse, so I should know then if it's the fan. As the AC is kicking in I'm doubting it's the compressor although a regas is probably required, but that wouldn't kill the fuse?

Any suggestions?

Check the alternator is not putting out too much voltage when the ac kicks in, as this rise in voltage will also cause a current surge through that system as it's drawing the most

I've had a similar problem with a Ford Galaxy. The AC compressor was in the early stages of failing.