What causes a 1994 Geo Metro engine to stall when the AC compressor cycles on?

A Geo Metro may stall when the air conditioning compressor cycles on because the engine doesn't have enough power to run all of the accessories and still maintain a high enough idle speed. The compressor will draw a lot of power from the engine and cause it to slow down. This results in a drop in oil pressure which will cause the engine to stall. To fix the problem, you can either increase the idle speed of the engine or reduce the load on the engine. You can increase the idle speed by adjusting the idle air control valve or by increasing the throttle stop. You can reduce the load on the engine by removing any unnecessary accessories or by reducing the power consumption of the accessories.