If you hear the relay clicking , then the sensor side of the circuit is working and pulling the relay in [ coil is being energized]
So, your problem is on the load side of the circuit.. that means contacts in relay or, more likely, load fuse for high fan.. Have you found a fuse for high fan??

I will send the schematic and then you will plainly see the load circuit...pretty simple, just some contacts in relay feeding the fan motors- no resistor in the circuit..
I personally think you have No power at realy contacts [load fuse]