It should vary the fan speed as needed to maintain the temp.
I'm thinking swap the CCU is with a rebuilt unit unless someone has a "but wait, check this first!" idea.
Looking through a search on "CCU" - this is the closest match I could find to my problem:
126 CCU "clicking" Update (possible fix?)
--->"clicking" noises. Only happened during cooling cycle, and only when the temp got to the point of regulation, when the CCU switches on/off to regulate temp in cabin." <--- that is pretty much it, but the clicking wasn't effected by driving (rough roads)