Abstract: A thermal management system is disclosed for a hybrid vehicle having an electrochemical power source (battery/fuel cell) and an internal combustion engine. In cooling mode, the system will flow liquid refrigerant over an evaporator attached to the battery/fuel cell, a two-phase mixture will then flow to the condenser where the heat is dissipated to ambient. In cold conditions where the battery/fuel cell needs to be warmed, the system will pick up heat from the engine and pump the warm fluid back to the battery/fuel cell until its optimal operating temperature is reached.