Pls check the refrigerant ( freon ), and pressure, in your AC Compresor, If your AC coupling off if you accelerate the car on static condition, it would be the freon in your AC system not enough, so the when you accelerate the pressure rise due to the AC compressor RPM's up, and the AC safety pressure valve cuts off, to protect your AC comp.
Try add the freon first, check for pressure and leak...
I have problem like you with my 740 89' and it solve with add the freon and servicing the Evaporator leak....
Good luck....

The first thing I would look for is the vaucuum lines under the hood, check all vacuum lines especialy the nylon ones. Second look at the plastic check valve near the intake manifold where the nylon hose goes into, my 88 760tic has two of them, take them off and clean them out and check them, you should be able to blow in one end and not the other. They are pretty expensive to replace, $27 at the dealer, so if one is bad you usually can clean them out and get it working again. Third check all vacuum lines underneith the dash, you can check all of them with a vacuum pump at the control switch(passenger side, underneith the glove box) and check all the servos to see if they will hold vacuum. (servos are on the drivers side near the accelerator pedal)

Good Luck