I suffered from this common fault, so, followed the excellent forum threads. Having removed the centre console, I found that the aircon console retaining screw closest to the switch was overly tight, causing a constraint on the switch. I loosened it to a very low torque and hey presto, the aircon button was as free as a bird. Sprayed with silicon and refitted everything. First ever job on the Jag that has gone to plan!

 

Well done....