disley, for your info.
I ran my 300TE during half last summer (hot as you would know) and up until recently with a non functioning viscous fan, relying totally on the auxiliary fans. Temperatures were always between about 85 and 107 when the fans would cut in a/c or not. There was never any question that the fans managed the cooling well although they did work hard on a hot day.
Recently I replaced the VFC and the difference is dramatic. In the three weeks since, the electric fans have not come on once and temperature is always around half way between 80 and the next hash mark (100). So, even in heavy stop start traffic with the climate control on, the temperature never gets above about 92.
Sounds like your VFC may be cactus but the switching points in the rest of the system are still working as they should.
Have a look here. \/
http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/103/20-0020.pdf