How effective is the thermal control system and the liquid cooling garment of a space suit? Does it prevent sweating only for a small to medium workload? If an astronaut is sweating behind his ears there might be problems with the communication system inside the helmet and the vision might be impaired. Wearing a suit filled with some sweat for many hours during an EVA might be uncomfortable.
While I don't have a source document I can link, from talking with folks in the JSC suit lab, I have learned that in general, the EMU (ISS/shuttle space suit) cooling system is overpowered to a small degree, to the point that crew can become uncomfortably cold while working.
The suit does have a valve that allows crew to adjust the cooling rate. It's labeled on the right side of the picture below. Interestingly, most astronauts tend not to use that valve for the fine-grained control for which it was designed -- they just tend to flip it all the way to "C" when they get too hot and all the way to "H" when they get too cold. (again, no documented source -- just from conversations I've had)