Don't know if you got your fan problem sorted, but here's my experience. Some Astra G's have a fan control module and some have 3 relays for slow, medium and fast. Lots of folk say that cars with air con have a control module and others have relays, but we have 3 astras (2002 and 2003) with air con and all three are the relay controlled type which are switched by the ecu. If you have relays they are in a black box to the right of the battery, a fan control unit would be found under washer bottle which is under the left hand wing. I think you will need an ecu from a car that had the same method of fan control as your own. On a relay controlled car, relay 1 (slow) kicks in at 99deg, relay 2 (medium) at 102 deg and relay 1,2 & 3 (fast) at 105 deg.