I fully appreciate that this is an old thread but as this fault appears to be a VERY common fault, I thought I would contribute.
I too had this same fault on my 02 Laguna II. I found the instructions on post #202 very helpful and also the following YouTube video. The video is not in English so I personally could not follow what was being said. However the video does clearly show how to remove the Climate Control Unit from the dash and then how to unclip the casing to reach resistor 101. (PS the video is in Polish for those with the appropriate language skills that alas I lack.)
As mentioned in post #202 the resistor does have a tendency to move as you apply the fresh solder so I used light pressure on a blunt pencil to hold the resistor in place.
I can assure you that this is a very simple repair and works wonderfully well.