Exactly what he says ^^ if the heat direction is in the windscreen position the A/C is on (As it's a good dehumidifier so great for clearing the screen) regardless of the blower, this is IF the car is a MK1.5 model, MK2 is the same I suspect, the MK1 did not have this feature. For this reason this position is coloured orange on the control but it's not obvious, check this first.

Martin