Why do refrigeration compressors stall when switched off and on quickly; or, why do I need to wait three minutes before restarting my air conditioner?
The compressor compresses coolant on one side of a closed loop. If you shut off the compressor, you still have the load side of the closed loop full of pressurized coolant. That pressurized coolant makes it much more difficult to start the motor. A motor starting at 0 RPMs will want to draw large amounts of current. With an added load to the motor (pressurized coolant) the motor will draw excessive current and won't turn over.

Compressors are likely leaky and therefore will allow the pressurized side to slowly decrease pressure until it's equal pressure between tho two sides. If you wait 3 minutes, it's expected that the pressures balance out and you have virtually no load when you try and start the motor again.

A compressor running at speed has one side of the closed loop pressurized and so is under load, but in that case, it already has momentum to keep it going. Also, at speed the motor doesn't need as much current to continue spinning. 

Here's a graph depicting induction motor torque and current vs speed to help illustrate why this happens.