A multi-mode vehicle thermal management system is provided that allows efficient thermal communication between a refrigerant-based thermal control loop and three non-refrigerant-based thermal control loops, where one of the non-refrigerant-based loops provides temperature control over the vehicle's passenger cabin, a second of the non-refrigerant-based control loops is thermally coupled to the vehicle's battery system and the third of the non-refrigerant-based control circuits is thermally coupled to the vehicle's drive train. The refrigerant-based control loop may be operated either in a heating mode or a cooling mode and is coupled to the vehicle's HVAC system using a refrigerant-air heat exchanger, and to the battery thermal control loop using refrigerant-fluid heat exchangers. A valve assembly is used to couple and/or decouple the battery and drive train thermal control loops, thereby allowing these two thermal control loops to operate either in parallel or in series.