Clean the sight glass on the reciever/dryer and check for visible bubbles while the compressor is running. If you see some, the system is probably undercharged, so the suction side pressure drops too low, the evaporator starts to freeze up, and the temp switch kicks the compressor off until the evaporator thaws. You will also see ice rather than condensation on the expansion valve if this is the case.

I don't know where the expansion valve is on the 190, though.

Normal charge for a Benz AC is more like 3 cans, though (85% by weight of what the sticker says for R12).

Peter

__________________
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!