[southern_cross]

It would depend on the situation. For a single room system, generally no; for a multi-room system, generally yes if the other rooms are empty or at least relatively less crowded than the one you're in. That is, I wouldn't expect the AC to really remove any CO2; it might redistribute it, though.

[rusticpenn]

The exhaust for ACs are generally outside the room, so there is an airflow..

[southern_cross]

Heat dumping is done outside the room, of course, but that's a separate airflow, one that's generally disconnected from the room. The cool AC flow itself is usually a closed cycle of some sort. You would be kind of defeating the whole purpose of trying to cool and dehumidify the air if you did otherwise, plus your AC system might have to run continuously in order to get anything done. There will always be some leakage, of course.