Drivers side near top of clutch pedal is a control unit with two green connector blocks, one with 2 wires & 2 with 4 wires. That controls the fan speed control air con auto etc.
Held by two 6mm A/F hex screws.Little awkward to get at best done with 1/4" drive socket set.
Item from citroen costs £50+vat second hand approx £30 delivered.
Just replaced mine took less than half hour.
Tony
January 2008