A/C fire wall plugs/caps

Anything that will stay on and fits snug will work, I usually use some caps I find around at work or I get with parts I order. Just needs to keep moisture out of your system, also be careful if your system still has refrigerant in it, it can cause frostbite and blindness. It isn't terribly critical you keep it 100% air free as you'll need to evacuate it before you recharge it anyhow.