duno if you got an escos, of saff.
but i had the same problem on my escos last week.

the wires to the fan we completly knackered, as was the switch (looks like a small water leak had slowly corroded them. the fans worked with air con but not on cooling circuit.

simply replaced the wires, work fine now. Duno if saffs the same but on escos there a green relay behind the battery which controls the fans, may be worth checking that?