If I'm driving in the city and have my air conditioner on, and I come to a stop where my revs drop, my car sometimes stalls. I can see my voltmeter drop to about 12v before stalling. I had a couple of amps hooked up before that I thought might be the cause, but this happens even without them hooked up now. Does this sound like a bad alternator? Thanks.

what mods do you have to the car?

the compressor clutch takes a huge amount of power to spin with the belt.....but i'm not sure why it would stall out....the car's rpm should go up when it senses the compressor clutch cycling on.

I think if you overcharged your AC with too much refrigerant, the compressor takes way more power. Or maybe the compressor is just going bad. I bet the voltage drop is simply because the engine is struggling & running at lower RPM before it dies.