So,there is good possibility it doesn't have any pressure left in the system? If that is true , then if I didnt have anyone evac the system, then replaced the 2 cores, I could most likely have a shop check for leaks and do an a/c service? Then the a/c should work again provided no leaks and problems with the compressor etc. thanks for answering my questions. P.s why would not doing the evac be a problem?

 

When you pull the evap core out you have to disconnect lines that bring refrigerant to the core and back to compressor. At which time it will evac if you haven't done prior. Take it to a shop and have it recovered.