The fans place an additional load and if the idle is too low, it could trigger a stall. If both fans are ON, are you saying that the vehicle stalls out when the A/C is activated? Could be a bad A/C clutch. You need to be more specific re conditions in which the vehicle stalls and conditions in which the vehicle runs w/o evidencing a stumble or stall. When the engine is cold, no problem? Only when at operating temp? Any codes?