If the old compressor failed badly, you will need to flush system out in order to protect new compressor from damage. Here is my method that we do at our repair shop.
Evacuate System
Remove compressor, drier, expansion valve or orifice tube.
Fill small amount denatured alcohol into all lines, evap core, and condenser
Blow out with shop air, hold rag on other end of each unit to catch oil and debris.
Install new expansion valve or orifice tube with new o rings, oiled to slip in easy.
Drain new compressor, you never know what or how much, if any oil is in there.
Fill compressor with proper oil as much as you can.
Put remainder of oil in drier and install with new orings
Reassemble everything with new seals / orings
Rotate compressor to distribute oil into lines
Vacuum system to 28-30" vac. For 20-30 minutes
Fill with proper amount freon
Thats what ive done for 15 yrs.
Other than manufacturer defects, no come backs on ac work
