Funny, I have a 2000 Disco II and I also think my AC fan is not working properly. My Disco would arbitrarily overheat when it's not moving, but usually it wouldn't overheat when still and never overheat when moving.
Not sure if the AC fan is supposed to be always on when the AC is turned on but I had the AC on and checked the fan, and it was not spinning. So I'm not sure if the engine temperature needs to reach a certain level or what.
Anyways, I did a search on here for "AC condenser fan" and saw several posts about replacing the fan motor. From what I gather, it's an easy job if yiu want to get a factory replacement for $300. Or you can get an '93 or there abouts Corolla fan motor for $45 to $75 from a junk yard.