You can use the air conditioning in ground operations with the APU bleed, the switches are always in ON positon. The air conditioning packs will automatically turn off in the moment you select IGN/START in the engine mode selector. It turns on again about 20 seconds after the second engine is on.
The engines can be started with gravity feeding, you will have the abnormal procedure ENG/fuel pump lo press 1+2 for both engines in the ECAM.