found this on another site hope it helps --------------
Fixed it at last!!!!
It was the blower fan controller. This is a unit about the size of a
cigarette packet and is found in the driver's footwell on the left, fairly
high up. Thanks to Paul at the Citroen Centre for telling me this.
Taking the unit out is awkward but not impossible. There are two sockets,
coloured green. One has a pair of thick wires (presumably power out to the
heater fan motor), the other has two thick and four thin wires, I guess that
this is power in and the vanbus multiplex control in and out. You need a 6mm
socket but I would recomment using a magnetic one in case you drop the
fixing self tappers behind the carpet.
Most of the bulk of the unit is a large aluminium heatsink There is a power
transistor inside the unit but I marmalised it trying to unsolder it. The
heatsink clearly seems to work when a soldering iron is used.
Having marmalised it, I had to buy a new unit. Much ferreting and phoning
around and I found that it is Valeo part number 509355 or Citroen part
number 6441L2.
I would recommend Neil Goodall at Vantage Citroen parts 0208 544 9997. He
keeps most Citroen bits. Cost is less than 40 squids plus the dreaded VAT.
Hope this helps all the other people who have reported thae same fault. It
is probably no more than a ten minute job to change the unit for a new one.
michael
February 2010