I have purchased a 1980 240D and it has become my labor of enjoyment. I am going to replace the AC compressor, AC drier, pressure switch, and expansion valve. This model takes GM radial R4 compressor. I know this may sound elementry but how do you loosen the drive belt? I am use to seeing a pivot bolt and slide channel. Any do's and don'ts when doing a project like this? Do I have the system flushed before or after installing the new parts and charging?