2001 Other Mercedes Benz Models Aircon always on when fan tu

Hi I have an A-Class Merc and the aircon seems to come on irrespective of whether the switch is on or off when the blower (fan) is turned on.

The lights on the A/C and Econ switches are off and the aircon can be heard to engage (when turned on) and disengaged (when turned off) when the aircon switches are toggled.

When the blower (fan) is turned off the air is normal outside temperature.