A320
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
During preflight the cabin cleaners and flight attendants complained of dirty sock smell in the back of the airplane. The APU was supplying bleed air to the packs with the engines shut down. I closed the APU bleed and notified maintenance.  The mechanic deferred the APU. Due to the persistent odor I opened the L1; R1 and R2 cabins doors and ran the air conditioning off external high pressure to attempt to remove the odor. While the smell slowly dissipated; it was still very detectable when we were swapped into a different aircraft 30 minutes or so later.
Air carrier flight crew reported a fume event during preflight while parked at gate. After maintenance trouble shooting an aircraft swap was ordered.