My wife has a Ford Ka from 2014 (so brand new really), whenever you set the fans to blow all air onto the windshield, it also enables the aircon.

I'd rather be able to control whether aircon should be on or not myself, so is there anyway to prevent this automatic "feature" ?

I've asked the dealer, but they didn't know :(

Nope. It's been standard on many different makes for quite a few years now.

The AC dehumidifies the air too, so it clears the screen quicker

Why not stick it on windscreen and feet instead?

Its been standard on a lot of AC cars for about 15 years lol.

I'm currently setting it on windscreen and feet, however it's quite cold for my feet until the engine heats up and doesn't really do much to prevent the windshield from fogging up

And the reason I don't want AC enabled is because when the engine is cold, I can only blow cold air onto the windshield (obviously), and if I enable the AC on top of that, the air gets VERY cold, which in turn cools off the window to very low temperature. This means when I either increase the heat or disable the AC the windshield will fog up immediately.

On my previous Toyota Aygo, Honda Civic and my current Fiesta I can choose whether I want AC when targetting the windshield - the Ka is the first car I've seen where it's not optional but in fact forced.

Had I known before I bought it I would actually not had bought it, it is, for me, that big a nuisance.

Anyway thanks for your replies to the topic, I'll have to work with what I've got :)

Put the Knob between windscreen and whatever is next to it in a mix, that will stop the AC coming on.