CAR DIES WHEN A/C IS TURNED ON, OTHER THAN THAT RUNS GREAT!

Ignition switch.

Sounds like the compressor is dragging the engine down. The compressor runs in ac and defrost mode. You might try unplugging the compressor to verify.

car stall out at stop light could be faulty idle air control valve or power brake booster has leaking diaphram causing large vacuum leak.

CHECK THE IDLE AIR CONTROL VALVE IT TAKES OVER WHEN YOU LET OFF GAS MAY BE STICKING

If it has that pressure when it dies, or is losing power, then it must not be fuel-related.
Just a thought: Do you have a large air leak from a faulty brake booster? I think you would hear air hissing when brakes are pressed if it's bad.Might check that.

CHECK IDLE SPEED SHOULD BE 650 - 850 RPM. IF IDLE TOO LOW AC WILL PUT DRAG SLOW DOWN ENGINE CAUSING ENGINE TO STALL IF IDLE SPEED IS TOO LOW.

check your idle air control valve, when you turn the a/c on the idle air should increase to help keep engine stay idle.

check the air flow meter.

Bad coil or Igniter