Well, the fan never truly freewheels. I believe the clutch is a viscous clutch that allows more slippage when the engine temperature is cooler, and less slippage as the temp climbs.
It's pretty easy to see why this is true -- at any time the vehicle operator may engage the AC compressor (either as part of defrost function or for cooling the passenger compartment).
Mere seconds of no airflow across the AC condensor can cause such a pressure spike in the system that it damages the compressor, blows a hose or causes coolant to vent to the atmosphere.
Then you realize that all cars either have an electrically activated fan (for instant airflow any time the compressor is engaged) *or* a clutch fan that never totally freewheels.
Electric fans are also nice for deep-water fording -- you're less likely to have radiator damage from an electric fan, as the blades hit the water and bend toward the radiator fins.
I've not electric fan(s) this on the Grand Cherokee but I have done it on other vehicles. It's not at all hard to generate enough airflow for cooling -- it's a little harder to generate enough airflow for the AC condensor!
Especially on a hot day, the condensor really needs some good strong airflow. The easy setup (if you have room) is a small-to-moderate-size 'puller' fan behind the radiator, and a similar size 'pusher' fan in front pushing air into the condensor. In our Grand Cherokees, there's not much room up front for anything in front of the condensor, so you probably have to stick with a single-fan solution.
It would be nice to hear what's the best fan to use (big enough to provide the power, small enough to still fit behind the radiator, and preferably reasonably quiet). The mechanical fans can use a surprising amount of power, and the electrical ones as well, but the electric fans can truly freewheel -- be turned off -- and would stay freewheeling as long as your airspeed remained enough to cool the engine (around 25mph) or higher.
Of course you want it thermostatically operated, but a kill switch would be great for deep-water conditions. Might be worthwhile to run two smaller fans rather than a single large one, depending on how it all fits in there . . .