No air from the center vents on max cool (thumbwheel on min, button with black up arrow and white down arrow selected) could mean no source vacuum or a problem with the diverter actuator. I think you'd get some air from the center vents if there was no source vacuum because the center actuator would be at rest with the center vent flap open. That would allow some backflow to the center vents. Do the defrost vents close when it's on max cool? If so, you have source vacuum.
The center actuator of my SD is bad so I get heat through the center vent. Take that, MB
The compressor is long gone so there's no AC.
I don't know about any green line. Sounds like something you'll find in Boston.