This item sits on top of the aircon compressor under the hood. It has a twist knob on top of it with a 2way arrow. To be exact, it is next to the oil filter cylinder. My car is the 1994 C180 Euro. What is this item? What will happen if I start to twist the top knob either clockwise or anticlockwise? I thought this was only in the diesels, maybe there is another lookalike in the diesels.