his carbon filter setup works .. hes pushing air out of the grow room thru the filter and into the outside air.
and looks like the AC was providing the intake air ... musta dropped that in the last pic but yes you will want fresh intake air to replace the air pushed out by the fan / filter combo. you can do this via passive intake ... ie: a hole with a light trap to allow fresh air in and not light ... or you can do it by forcing cold air in via the AC you showed in previous pics