There are reasons
Brother of The Benz, Jayhawk
To answer your questions lets go one at a time:
Not cooling at idle can result from
1. a low gas charge
2. low suction pressure resulting from a worn compressor or No. 1 or 3
3. slipping belt
Have your system checked by a technican if none of these are obvious.
Viscos fan clutch.
Most of these can be stopped as you have yours and still be able to perform satisfactorly.
To remove the fan clutch the radiator does NOT need to be removed. There are fan shroud retaining clips holding same to the radiator. By removing these in the up motion, the shroud is laid back over the distributor and the fan is exposed. You will need a special socket wrench and anti-rotating tool to remove the fan/clutch assembly. I'm not familiar with a test procedure for the thermostat in the fan/clutch and it is to be replaced. Fastlane has the tools and the fan/clutch.
Happy Trails Beep Beep from The Spiderman in Houston!!!