I just noticed that the radiator funs for my Jaguar X-Type 2004 are not running. They however start running when i switch the AC on.

What could be the problem and possible solution

 

I would start with electrical diagram. Find diagram, post it here.
Usually PCM grounds wire going to fan relay, sometimes fans have variable speed and fan control module. Some cars have 3 fan relays

 

Africa, with the X-Type, the fans will not run unless called for. The fans will be called for whenever the engine temperature gets too high (above 205F or 97C) or the A/C is called for (which is also happening when the defroster is used). As for the speed that the fans will run is also based on a few variables. When it comes to the engine temp, the more above 205F you get, the faster the fans will spin. Same thing with the A/C. If you have it on a low demand, the fans will spin at a slower speed and may even turn on and off. Where, if you ask for maximum cooling, the fans will immediately go to fast speed and not turn off.

 

Count your blessings, it's an indication that yours are behaving as designed. Converse to the hundreds of other posts about fan (& fan module) problems.