Cooling Fan switching on/off too quickly when running AC

95 GTI VR6 with 140K miles and "running" strong except - yesterday temps
were in the 90's and in traffic my AC started making a growling noise then
shut down and then turned on after a few seconds then off. After car
started moving turned system back on - quickly cooled no problems. During
idle high speed fan will turn on for a few seconds then switch off and then
cycle again. Took the car to an AC specialist - but not VW specialist and
said pressures were fine but he did notice the fan switching on and off
which could if the outside temps were high enough could cause the system to
get too high of pressure and shut down the system since the fan isn't really
cooling down the coil. Ok, but what would fix the problem - radiator
switch, switch located on the thermostat housing or is it the Fan Control
Module?
Is there a way to test the Fan Control Module?