There are a number of threads addressing exactly this issue so a SEARCH would turn up the answer your looking for......
The most likely cause is a blown thermal fuse in the resistor pack - the glovebox picture at the start of this thread shows where it is.
Remove the cable connectors and locking screw and twist and remove the plastic moulding containing the resistor
and thermal fuse, up and out of the main air pipe....be careful not to damage the
. (Ignore the automatic hyperlink that links the word '
- nothing to do with this problem).
Once on the bench, carefully remove the metal cover using thin pliers to untwist the locking tabs - note which way it fits back on.
for any burning or breaks.
The thermal fuse is the small 'bullet' shaped device at one end - put a simple continuity meter across it to see whether it is conducting. If not its blown.
The temperature is printed on the outside (about 100'C) you'll need to get one from Maplins or RS - again various threads list the part number(s). Get one that can handle a significant current - suggest about 10 -12 Amps.
As its a thermal fuse, soldering risks heating the fuse to a point where it 'pops' again. Cut out the old leaving enough lead to attach the new and either solder the new one in place with some sort of heat-sink on the fuse body OR attach with a mechanical connector at each end.....the metal terminals inside a 'chocolate block' strip have been suggested as quite a good way to do this.
Quickly check it is still conducting with your test meter - carefully re-assemble the pack and re-mount in the main air tube.
Its a good idea to inspect the main tube / blower fan casings for blockages -(usually leaves and twigs), which might have caused the over-heating problem in the first place.
Your blower control will probably now work.
Alternatively, buy a new resistor pack from Renault - about £60 I gather!