Bad belt (unlikely, that usualy requires re-starting car) or coolant temp going too high. Check aux fan and visco clutch, also radiator for blockages.
High coolant temp (over 110C) will shut the AC compressor off.
Could also be a bad Kilma relay, but you need to check the inputs before replacing it.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!