Dometic Environmental offers auxiliary air conditioning sytems for trucks. These units keep the sleeper cool when the truck's engine is not running, saving idle-related fuel costs. Truck auxiliary air conditioners run on 115 Volt AC power. This can be supplied from an onboard generator (often called an auxiliary power unit, or APU), from a shorepower hookup or from an inverter, a device that converts 12 or 24 Volt DC power from batteries into 115 Volt AC power to run the air conditioner and other electrical equipment in the sleeper.