When opening ANY a/c component, it is ALWAYS a good idea to seal it up. Moisture and other elements in the air tend to cling inside these parts and can be difficult or impossible to evacuate. If the part is being removed and is small enough, wrap it up in a plastic bag. If the component is being left in place, find a way to plug the end.

It is illegal to do so today, but in the old days (Yep, I'm plenty old enough to remember them) we would "sweep" the system with just a small blow of refrigerant before sealing and evacuating. We did this by leaving a line or two loose and with manifold and refrigerant attached, just blew an ounce or less of refrigerant through the line to blow out the air, then immediately connected the item, sealed everything up, disconnected the refrigerant container and connected vacuum pump, then started evacuation. Of course, since this vents refrigerant, albeit a tiny amount, to the atmosphere, it is illegal to do so today.

Form the looks of your pictures, you have a little further to go. Once you see bare firewall, then you know you're close.