H Freddyford. I have manual air conditioning in my basic trim ecosport, by turn cold up and down to suit manually, and it just runs without cabin control, and had recirc switch, so pretty straight forward. By opening a window it does not affect it.
Whereas you will have climate air conditioning, it should have recirc switch , and that it has a cabin sensor to control your cabin desired temperature setting, so it will hunt on and off to your desired cabin temperature, so you get right hot and cold mix to reach cabin temperature. By opening a window will affect climate control, and it will just keep running as it will not reach cabin temperature, as cabin is no longer sealed.
If your climate control is not hunting on and off to keep to desired cabin temperature, then culprit will likely be cabin sensor.
PS...My wife's smart car (Fortwo) has climate control, and I hate it hunting on and off, and I put a window down a bit (2 inches, 50mm), and it no longer hunts and remains on all the time, as it cannot reach desired cabin temperature.
Hope that helps.