Is this the big fan at the front of the car in front of the radiator that serves both as a cooling fan for the engine and the air con. If it is, it is worth checking the condition of the relays that control the fan as these have been known to fail, even if the motor itself is still operational.
If you go back a few days you will find a whole thread on the subject
There is a primary external relay in the fuse box which is easy to check
But the ones we are talikng about are the relays built in to the Fan housing there are three of them (CDT) before buying a replacement unit try and establish if one of those have failed first
It still means you have to take the fan off but you could find the existing one can be repaired pm Rover Ron he has one all in bits in Scotland at the moment
In fact Mods I seem to remember someone posting a brilliant post with pictures of taking the front of the car apart, if we merged that with the other Fan thread and made it a sticky that might help as this is becoming a very common question
I only mentioned it has there has been reports of the relays in the motor assembly failing whilst the motor itself is fine. There are several windings in this motor for the different purposes the fan is used for including engine cooling, and air con, with separate relays to operate each circuit. The fans fitted are also engine specific. Car Mechanics mentioned this in the Rover 75 series they were running a couple of months back.
A relay is just a magnetic switch whereby a low current circuit activates a solenoid coil to open or close contacts on another circuit carrying (usually) a higher current.
Search under Rover Ron as he was looking at a failed motor to see how the relays can be replaced without having to replace the whole motor which as you have just discovered isn't cheap. It is poor design in my opinion to have an assembly which would be scrap on account of a relay costing no more than a tenner.