I have 2004 Cooper S 82,000 miles. Started car hit A/C switch while moving, nothing happened. Tapped switch several times, nothing, at first stoplight turned off car restarted and hit A/C switch and on it came. Whats going to happen? Would like to be prepared.

 

This isn't enough information to predict what is wrong. I would use a set of gauges and measure the high and low side pressures. If pressure is low, there is a safety switch that will keep the compressor from running.

Can you look to see if the compressor clutch is working (the AC pulley spins all the time, it has an electromagnetic clutch that makes the second part spin when you call for AC).

Check all the fuses.

Does the blower operate inside the car without the AC?

Is the electric fan in the engine compartment running when you call for AC? (The fan attached to the radiator).

 

I would change one process and then not think about it unless it happens again:

Let the "systems" "power up" while the key is in run before you start the engine.
Key on, Instrument panel lights come on, later some lights go off, then start the car.

I have had at 3 different times, different components not power up when I'm too quick to start the engine:
Electric Power Steering not come on. Boost Radio not come on. AC Clutch coil not come on.

If I turn off the key, turn on the key, wait, start the engine, I've not had a problem with these systems.

I broke the AC Clutch coil a few weeks ago, but it was working until I floored the hell out of it trying to merge in with traffic.