I have been hunting down a slow leak in my 1987 325ic air conditioning system. I've been using Rob Siegel's great book, "Just Needs a Recharge". One thing I cannot figure out is, what on earth that thing is under the right side shock tower brace. Below are a couple of annotated photographs. I’ve searched the internet (although THAT is never complete) and the E30 Bentley Manual. I can find no diagrams or photos describing it. The expansion valve for an E30 is beside the evaporator in the passenger compartment, so that’s not it. The mystery device has what appears to be two lines coming off of it, one of which does a complete 360 circle around the engine compartment. I’ve traced the lines and one leads to the front of the engine and the other seems to lead to the back of the car. They may be vacuum lines. It just doesn’t fit into my understanding of how an a/c system works. It makes no sense to me. Can anyone explain to me what the mystery device is?