I was looking also this way out to cool down my (future) car, through electric compressor...... seems none of them actually working really on 12 volts, but the motor is or 110vac or 220/240vac.... and converted from12 volt battery... some times the converter is stand alone, or found a few with build in , on top of the compressor motor,..... and that's why you need at least 55 amps over 12 volts to feed the thing..., so big alternator & battery needed........
Paul