Replace your serpentine belt, it's slipping and the Klima relay is switching the compressor off.
You also need to find and fix the leak, then evactuate (apply a hard vacuum for an hour or more) the system BEFORE charging, especially with R134a -- water vapor will cause the formation of hydrofluoric acid. The acid will corrode EVERYTHING in the system, including the teflon coating on the compressor pistons!
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!