I dont believe your AC has anything to do with your problem! The shaking may come from your harmonic balancer not being seated correctly and the stalling can be from many differnet things but i would start with the distributor.
Prior to weighing anything on a balance, you would want to lay a piece of weighing paper on the pan and tare the balance (zero it out). Following this, you could use a clean metal scoop to transfer solid to the weigh paper for weighing.
I don't think so since its purpose is to balance and cancel vibration. It is mounted on the opposite end of the engine. Usually the crankshaft sensor fails because of oil contaminating on the sensor. Difference in temperature with the oil causes the sensor to malfunction intermittently.