I've replaced everything on my CA B12 and they still won't kick on by themselves no matter how hot it gets. This after a full rebuild. Comp. test and block leaks aok. I've had a switch put in so I can manually switch the fan on/off. This made a world of difference.
I am told the next thing to replace is the 'Temp. sending unit' which is next to the temp sensor on the radiator.