So I have a 2001 Expedition eddie bauer, and the rear a/c doesn't seem to get cold. The front get's cold -but not the rear a/c.

Is the rear a/c a complete separate system? could it need charging? and if so, where is the low side "port" ??? I couldn't find it anywhere.

I'm reading about blender doors, etc... I HAVE NO CLUE. Someone point me in a direction to start, and I can go from there.

 

The rear system is not separate. The front and rear systems share the compressor and condenser. With a low refrigerant charge, it's usually the front that wheezes out first.
Without the system pressures it's only a guess, but I think you have a blend door actuator issue in the rear unit. It's common. The evaporator is getting cold, but the door never directs air over it for cooling.