Auxiliary power unit

The present invention is directed to an auxiliary power unit for use with a vehicle, typically a truck. The truck has a cab and a sleeper to which the auxiliary power unit provides auxiliary air conditioning and heating. The truck also has a cab evaporator, a sleeper evaporator, a compressor, a condenser, and a plurality of refrigerant lines, a cab heater, a sleeper heater, and a plurality of coolant lines. The auxiliary power unit has an auxiliary evaporator and a plurality of auxiliary refrigerant lines. The auxiliary evaporator is arranged in series with the sleeper evaporator and the sleeper heater. The auxiliary refrigerant lines are separate and distinct from the truck's plurality of refrigerant lines. The auxiliary power unit also has a plurality of auxiliary coolant lines which are interconnected with the truck's plurality of coolant lines. The interconnection is accomplished in such a way that the auxiliary power unit can provide heat to the sleeper heater when the truck engine is running or when the truck is not running. If the coolant becomes excessively hot, a by-pass thermostat and valve direct the coolant to an auxiliary radiator. The auxiliary power unit has an auxiliary control panel in the sleeper to provide control of the heating and cooling in the sleeper when the truck engine and/or auxiliary engine is running.