(.....actual availability depends on market region – see below).
In the North American market (USA / Canada), ECC was not offered as an option on their 740 & 940 at all, while ALL of the 960 & S/V90 has ECC as standard equipment. In Australia the 740 & 940 received ECC as standard equipment on both Turbo and 16 Valve models from 1990 (the 8 Valve naturally aspirated models retained MCC), and I’ve also seen late model 960 (1995 onwards) with MCC in Australia.
The most important component of the ECC is the control panel itself, which is basically a small computer receiving inputs from 3 temperature sensors (ambient temp. sensor near the blower fan, engine temp. sensor near the heater matrix, interior temp. sensor hidden in the dome light), and a solar sensor on the dash. ........
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Perhaps marketing department had some ideas that didn't materialize for after-market kit.
Unknown, but it may be related to how vehicles are assembled...