as I have mentioned I experienced a similar problem in my 190, aux fans worked when I disconnected the sensor and the ac did work a little, I could heat the compressor engage and feel the engine rumble when I turned the ac on, but it just wasn't cold enough. I say evac and recharge because someone had also mentioned something about air pockets that could be causing you problems as well. In my case I only had 3 ounces of refrigerant in my system when the guy checked it for me. he didn't find any leaks either as he explained to me that he injected a dye in the system. its worth a try, no other way to tell if there is something else wrong unless you know for a fact that the system is fully charged with no air pockets

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1990 190E 3.0L