Abstract: An automotive heater and air conditioner in the form of a closed circuit reversible heat pump in which one internal heat exchanger accommodates both heating and cooling, selectively, and only a single set of ducts is required. Supplemental energy is provided in the system by using external heat exchanger means in close exchange proximity to and served by the waste heat of the automotive engine. The single exchanger selectively functions as evaporator and condenser. A reversible expansion valve functions between the external and inboard exchangers permitting selected conversion of the exchangers from a condenser to an evaporator function. Valving around the compressor permits selected directional control over refrigerant flow. The compressor can be selectively disconnected to turn off the heat pump. Air controllably ducted through, over and around the inboard exchanger is circulated into the passenger compartment to cool the occupants, to warm the occupants, and to defrost the windshield.