A truck includes an auxiliary power unit having components specifically selected such that they form a stand-alone unit that can fit within an auxiliary compartment of a vehicle and deliver heating, cooling, and additional electric power to the vehicle. Included is an auxiliary engine, an auxiliary alternator, and an auxiliary condenser to provide coolant for a personnel compartment mounted evaporator. An auxiliary voltage regulator provides a ramp-up feature to minimize excessive start-up loads, limits maximum available current from the auxiliary alternator when the auxiliary compressor is engaged, and selectively disables power to electrical components in the event of low vehicle battery voltage. The auxiliary engine includes a radiator system to provide heated fluid for a personnel compartment mounted heat exchanger.