Hi everyone...new guy here. My friend and i are almost done with an engine swap on an '04 Colorado with inline 5 cylinder. During the course of removing hoses, etc. from the old engine, all the freon was lost from the A/C. I was wondering if anyone could tell me if the A/C has to have the air removed before you can add more freon, or can you just recharge it without having this done?

 

In order for the AC the function to full potential the system should be vacuumed for a minimum of 45 minutes.