In much cooler weather the compressor will cycle as needed, but in this hot weather it will most likely stay on constantly.

Do you think you could post a video of you cycling the AC compressor on and off so that we can get an idea of the load that the compressor is putting on the engine...

From what i can tell just by reading your posts, i think your compressor might be a faulty unit.

Leathermang, a 1980 300SD has the servo system, horizontal pushbuttons w/ compressor on/off switch. Which would be ACCII.

__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg