A/C how many ounces are in the large tank?

If you don't have the rear A/C it holds 42 oz, if it has the rear A/C it holds 68 oz. However, what is the reason it's empty? If it is from leaks or component replacement you will likely need to add some oil as well. You will also need to pull a vacuum if it was opened or has been empty for a while to remove any moisture before you can add anything. Unless you are an AC professional with 609 certification you cannot buy anything but the standard cans legally, so a 30 pound isn't in the cards.