It sounds like you haven't installed all the wiring for the Hyraulic fan.
The hydraulic fan is completely independent of the ECU, and runs on its own sensor ( the one in the radiator).
So I'd either fix the system, so it works properly, or piss it off, and replace it with a normal clutch fan, or a pair of AU thermo's.
FWIW the Hydraulic fan is a brilliant system when it works perfectly, but I have no doubts its fucking useless when it doesnt.
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