It starts as a squeal that gets progressively louder when you switch on the air conditioner. Then, more alarmingly, smoke appears from under the hood as the A/C quits working altogether. The squeal becomes deafening, and you frantically turn everything off before raising your hood to find oil and smoke billowing out from the A/C compressor. The prognosis is not good. Your air conditioning compressor has gone to the great compressor graveyard in the sky.