If it is a standard installation neither. Using attic air for the supply would certainly cause problems. Out side air, is usually a high end option and would require some controls to make it work correctly. You would be able to see a grill outside of the house that would different. Typically the air is drawn in from the house through a filter/return and then through the airhandler, then back into the living space out the registers. These units work just like every other a/c except the condenser/compressor is remote to the inside coil.