Alright, I am throwing out a couple ideas for you that you might want to look into. First, when you are talking about "A/C actuator" what is the actual technical term for that part? I haven't heard of an "A/C actuator", but there is a couple of diaphrams in that area that you are talking about. Next, I don't think that, the hoses and all that are your problem. Have you took the head unit in and had it looked at? Try pulling out the headunit if you have the keys and making sure that there are no wires that are crossed. I am looking at your car as being the first year the W202 came out, so it is getting up there in age. Have you ever removed the headunit before? Is this the stock headunit or has it been replaced before? The problem definitely sounds like a headunit problem and I would go get that checked before you start putting a hundred dollars here and a hundred dollars there on hoses and stuff. Well, I hope that helps out, let me know what happens with that. If I am completely off on my theory tell me what it was, so I know for next time.