fan clutch drives when the air temperature through the radiator exceeds the thermostat setting of the clutch.
220* coolant temp is too high.
Where did you read 70% ?
A fan clutch will totally lock up when engaged
It disengages by temperature and high rpm.
I have gotten the best service from Imperial brand.
I also don't like HD rated clutches, as they don't disengage by rpm until a higher range, and become audible in the vehicle at 40-50 mph when you shouldn't need a fan anyway above 30.
I made a mistake once and installed a HD one on my "TownCar" (high gear w/OD) and at 100+ ambient it hummed until 78 mph.
Took it back and got a standard duty.