It really is a shame that the ACC Sensor doesn't have any heating. Just a little bit of too warm + snowfall and you have a blocked sensor.
When it gets blocked the ACC just goes standby. It is still on, but won't set. You need to scrub the snow off to get it running, but still the same problem after few kilometres.
However, at least in my F31, you can switch to normal cruise control by pressing the ACC distance buttons (closer or further, no difference) for ~3 seconds. And this works also, when you have a "blocked sensor" -error on.
you can also switch between ACC and normal-CC with the same manouver. Just when you go from CC to ACC you just have to tap the distance buttons.
Driving: F31 320xdA, E82 135i DCT, Mercedes-Benz Sprinter 319CDI A3A
Ex: E91LCI 330xdA -10, E84 X1 20xd, VW T5 2.5TDI 4Motion, Citröen Ax 1.1 injection -91