I can help you partially. The cooling fan in front of the condenser (auxilary cooling fans) come on when the pressure raises above a certain point. This pressure increase will happen at idle. If the car sits for more than 5 minutes or so on a hot day and the fans don't come on, then there is a problem. I know our cars are different but A/C is still A/C.
You should be able to test the pressure switch by removing the two wires from it and touching them together. If the A/C is on, the fans should then come on as you are completing the circuit. My pressure switch has two wires, Im not sure about yours as I've never looked closely under the hood of a 220. The pressue switch will be a small cylinder looking piece that is about the size of 8 quarters stacked up. It will have an electrical connection going into the top of it. First place I would look is your drier as that's where MB usually puts it I believe.
Regarding the power coming on then off, it sounds as if you have a low charge to be honest. That could cause all your problems. I think there are two different pressure switches? One controls the aux. cooling fans and the other will control the compressor cut-out. The low pressure switch cuts the power to the compressor if there is low pressure. Low pressure would be a result of a low charge. If there is not enough pressure (thus not enough refrigerant) then there is a shortage of oil. The oil is mixed with the refrigerant so when the refrigerant leaks, so does the oil. This switch could probably be tested by once again jumpering the two wires together and see if it stops the compressor. To me, it seems like your compressor is short cycling because of the low refrigerant and the other switch (high pressure switch) isn't being activated because with the low refrigerant, the pressue doesn't get high enough to trip that one off.
So, in reflection on my long post, take it to the dealer or A/C shop and have the pressure checked. They'll hook up guages and can tell what your pressure reading is at and the dealer could tell you what the pressure should be at to trip the different switches for their individual function. If you lived closer I'd come over and help you out for a Pepsi
(The dealer will charge more than a Pepsi for their service)
Thanks
David