I have replaced my compressor but it won't hold a vacuum. But I can use compressed air and it holds . any ideals? and it will not take a charge.

 

If it won't hold a vacuum, you have a good size leak in the system somewhere. Are you saying no refrigerant will move from the can to the system or it won't hold it?

You need to draw a vacuum and have it hold first before proceeding with adding refrigerant.

I recommend reading up on EPA 609 MVAC and even getting certified. The materials are freely available online and it's an online test but the study materials are an excellent resource for learning how to service your car's a/c system.