If your original compressor has locked up, you must flush the A/C system. Failing to do this will leave metal debris in the system, and cause the replacement compressor to fail as well. Keep in mind, new multi-pass, 6mm tube condensers are nearly impossible to properly flush. You may need to replace the condenser. Talk to your A/C Technician for more information.
Use only R12 or R134a refrigerant. "Blend" or "Alternative" refrigerants are not approved by ANY of the major automobile manufacturers. If those refrigerants did what they say they do, the OEMs would be all over it. Some blend refrigerants, while they may improve duct temperatures, can cause problems down the road.
System Sealant. Or, What NOT to Use Again.
Avoid system sealers and leak stop. These products are band-aids, not repairs. Leak sealers react with air. If there is air in the system, the leak stop will congeal into a thick green jelly. Not only will it clog system components, your A/C Technician is not going to want to evacuate your refrigerant with his very expensive recovery machine. Further, he will be very upset if you don't tell him you have it in your system, and he does run it through his very expensive recovery machine.
These are some basic technical facts. CoolairParts will be adding and updating information as it comes available, but if you have a specific question, feel free to e-mail or click "Sales Chat" for an instant online text session.