There is a separate box inside the rear tailgate that feeds the overhead 6 vents for cold air and a low level vent for rear heat, its a £750 option and well worth it in a Kombi.
I don't think there is a compressor in the boot, its more of a fan box with a couple of actuated flaps with some super insulated pipes running under the floor to it. Its almost identical to the system we had in our Tourneo Custom.
I've got some photos somewhere which ill throw up at some point.