Why does your car shake when you turn the air condition on?

Answer 1

Possibly due to a failing compressor. The A/C compressor in vehicles has a clutch in it which operates by friction. If the bearings are going bad, or the clutch is about to lock up, it can overload the engine as it tries to spin the compressor. The excess load on the engine makes the engine want to slow down, but the engine is designed to compensate by trying to speed itself up to normal operating RPMs and thus continue running unless the starter switch is set to the off position. This battle can result in jerky motion from the engine, which is tied to the frame of the car by motor mounts, as well as the transmission to the wheels. If the car is in park or neutral, the jerking motion is transferred through the motor mounts to the car frame. If in gear, it is transferred through both the motor mounts and to the wheels through the transmission.