The switching OFF of the CAB FANS is merely to prevent smoke from entering the cockpit and cabin. Prior to that, the VENTILATION BLOWER and EXTRACT are selected to OVRD to extract avionics ventilation air overboard. AIR COND smoke will quickly trigger SMOKE warnings such as lavatory, cargo and avionics, nevertheless those ECAM procedures must be applied.
If AIR COND smoke is suspected the APU is switched OFF (if ON) and VENTILATION BLOWER and EXTRACT returned to AUTO (prevents depressurisation, single PACK operation may not maintain cabin pressure). Then PACK 1 is switched OFF. After 5 minutes, if smoke continues PACK 1 is switched ON and PACK 2 is switched OFF. After 5 minutes, if smoke continues PACK 2 is switched ON and VENTILATION BLOWER and EXTRACT are switched to OVRD.