For an engine to drive a fan it takes 40 horsepower. That's what a horton fan is designed to help, improving power and fuel economy. It allows the fan only to be on when needed. The Horton fan system consists of Fan, solenoid, a small little filter and the air tank.
The air is supplied to the fan from the air tank, through the filter to the solenoid. The solenoid controls whether the fan gets air supply or not. The solenoid is controlled by the ECU. The ECU gets inputs from the coolant temp sensor and the manual fan override switch. The air conditioner also affects whether the fan is on or not. The horton fan in principle is quite basic. The fan is driven by a belt. It has the fan bolted at one end. The hub is two-piece with a clutch friction lining in between.
It works by air pressure acting internally on a diaphragm closing the gap so the friction material contacts and drives the fan.
There's two different types of horton fans one that has the fan locked in with no air pressure to it and one that has the fan locked in with air pressure supplied. In the event of an internal failure you can get a lock-up bolt to manually lock the hub's together so that the fan is constantly engaged. A leaking air line will cause your Horton friction lining to wear out sooner than it should. Because it doesn't have the full pressure it's not fully applied, so it slips and that's why it wears. So it's a good idea to spray this line with soapy water and make sure it's not leaking. Another thing to check, obviously when the engines not running and the keys are not in the ignition, so that it wont cut your hand off. But get in there and see if there's any play up and down in the hub. There's a bearing inside the hub and if this wears out it will develop play. You shouldn't be able to feel any movement.