fan on all the time?

I was recently working under the front of my 1996 XJR, and noticed a broken wire, which I repaired only to discover that my fans were then on whenever the ignition was on. On further investigation, I discovered a) that my fans had been inoperative for some long time, and b) that they are intended to be on at low speed whenever the ignition is on! Although the wiring diagram shows two pressure related sensors for the aircon, in fact only one is fitted ex factory, with the wiring for the other shorted out, again ex factory. This was apparently a modification incorporated relatively early in X300 production, and seems fairly crude to me. The upshot is that if the aircon begins to exceed the set temperature parameters, the remaining switch will trigger high speed fan operation, rather than low speed which is permanently on. The connector where the shorting wire is sits above the brake servo, and can be checked easily to see the wire in question.
Is it possible that when fitting the new water temperature sensor, a fuse was replaced, or another wiring issue resolved, since what you are describing in relation to the fans sounds like "correct" operation as envisaged by Jaguar ( unless yours is one of the early cars) .
I have fitted a relay to mine to prevent operation of the fans unless triggered by the aircon actually being on, and calling for the compressor, which avoids the fans cooling a cold engine etc.
Please ignore all of the above if you are not an X300 owner!