Peugeot 306 1996, Air con not working at all?

Hi

We have a Peugeot 306 XR, and the air con does not work at all. The control panel in the car does not switch on, no green light comes on, no fan speed, fan does not come on at all. I have checked all fuses and found these to be ok. I have changed the control panel with one I bought from a breakers this does the same. Two units doing the same fault?? I have haynes manual but the wiring diagrams are not clear on where the voltage comes from, or on which pins it connects to on the control panel??(big blue plug on back of control panel)
Could it be a supply problem?? or will the temp control unit not switch the control panel on if low on gas??
Any help would be grateful.