Abstract: An auxiliary cooling, heating and electrical power unit for vehicles with large capacity internal combustion engines. The unit includes a small capacity auxiliary engine driving an auxiliary coolant pump, alternator and refrigerant compressor, a separate air conditioning unit and an auxiliary battery. A heat exchanger attached to the auxiliary engine transfers heat from the exhaust gases to coolant circulating through the heat exchanger. The coolant pump circulates the heated coolant through the main heater core and the main engine before returning to the heat exchanger. The refrigerant compressor provides refrigerant to the auxiliary air conditioning unit. The auxiliary alternator provides electrical power to the auxiliary battery, the main battery and other electrical equipment. An interlock prevents the simultaneous operation of the auxiliary engine and the main engine.