Hi,
Could anyone help me with that - when I set air con ON and to lowest possible temperature...
It takes for ages until it starts normally cooling. In all my previous cars (Ford Puma ´97, Mazda 3 ´06)
A/C was way quicker to set itself...
And anyway... Also after half an hour it still doesn´t "freezing" like it should.
I just think that I can change A/C fluid (if something like that exists)...
Or can someone give me an advice please?

Probably needs a recharge. Fiesta ST's are absolutely famous for failing A/C systems - if the systems aren't used for an hour a month the seals dry up and the gas escapes.

Mine's gone again for the 3rd time in 6 years.

Thank You. So do I have to refill a fluid then only?
Can someone guide me please? Ads I have never done something like this before...

think it's a garage only allowed job

you can buy the refill kits from Halfords £65 but loads of garages have offers so just go to a garage

Yeah, go to a garage. It's not a legal requirement for a garage to do it (the only legal requirement is safe and responsible draining and disposal of old refrigerants.

The kits you can buy are essentially refrigerant in a can, it won't get anywhere near the pressure needed for an empty system - plus with a garage they can tell you if the system is leaking or not.

in there today and saw some near the counter !