2 possibilities-1,fan control switch is faulty or 2,fan rheostat or its connector faulty.remove scuttle panel trims and wiper moter assembly.on the side of the heater fan box there is a small rheostat unit.unplug the connector and check its condition(a commen problem was the connector melting,connector kits avaliable from renault).if thats ok then check there is an earth to the connector(probably a black wire but i cant remember the pin number),check that there is a feed present when you select the different speeds(there is 3 other wires one for each speed,check that one of the wires has a feed down it when you select your different speeds.if all ok then the rheostat is faulty.if you dont get all the feeds then its poss the fan control switch on the heater panel or a broken wire between the switch and the rheostat.If you get stuck ill find the pin locations(rheostat connector)for the different speeds and the earth so that you can check it properley.jay