The a/c dehydrates the air, which helps a lot in getting rid of the condensation on the windows. So, the compressor turns on when the computer tells it to, not when you tell it to. Kinda sad, because I love the air movement of floor/defrost
Are we talking manual controls or auto climate? With the auto climate setup, whilst demist positions call the A/C to be on, the light *does* come on and you *can* switch it off again. The user controls override the computer.