You just replaced a compressorwhich failed mechanically what do pyu do before restarting the unit?

Answer 1

AC compressor? be sure to bleed out the air inside the system.

Answer 2

If you are talking about commercial/house  AC units, add a low side filter if it dosn't have one, (there could be metal in the system from mechanical failures)  pull it down with a professional grade vacuum pump to at least 20 microns. If it holds you should be ok to recharge with oil and refrigerant