A method of constructing modular air conditioning systems for vehicles, the method comprising: providing a plurality of identical universal base units each including a frame, a condenser, an evaporator coil, and a blower, each universal base unit including open-circuit refrigerant lines such that the universal base units are themselves non-operational; providing the following types of completion kits a front box kit connectable with any of the plurality of identical universal base units and including open-circuit refrigerant connection lines complementary with the open-circuit refrigerant lines of a universal base unit to define continuous flow paths therebetween, the front box kit including a secondary cooling coil, and a secondary blower, and a compressor kit connectable with any of the plurality of identical universal base units and including open-circuit refrigerant connection lines complementary with the open-circuit refrigerant lines of a universal base unit to define continuous flow paths therebetween, the compressor kit including an electrically-driven compressor; attaching the front box kit onto a first one of the plurality of identical universal base units to construct a first air conditioning system of a first type; and attaching the compressor kit onto a second one of the plurality of identical universal base units to construct a second air conditioning system of a second type. providing a plurality of identical universal base units each including a frame, a condenser, an evaporator coil, and a blower, each universal base unit including open-circuit refrigerant lines such that the universal base units are themselves non-operational; providing the following types of completion kits a front box kit connectable with any of the plurality of identical universal base units and including open-circuit refrigerant connection lines complementary with the open-circuit refrigerant lines of a universal base unit to define continuous flow paths therebetween, the front box kit including a secondary cooling coil, and a secondary blower, and a compressor kit connectable with any of the plurality of identical universal base units and including open-circuit refrigerant connection lines complementary with the open-circuit refrigerant lines of a universal base unit to define continuous flow paths therebetween, the compressor kit including an electrically-driven compressor; a front box kit connectable with any of the plurality of identical universal base units and including open-circuit refrigerant connection lines complementary with the open-circuit refrigerant lines of a universal base unit to define continuous flow paths therebetween, the front box kit including a secondary cooling coil, and a secondary blower, and a compressor kit connectable with any of the plurality of identical universal base units and including open-circuit refrigerant connection lines complementary with the open-circuit refrigerant lines of a universal base unit to define continuous flow paths therebetween, the compressor kit including an electrically-driven compressor; attaching the front box kit onto a first one of the plurality of identical universal base units to construct a first air conditioning system of a first type; and attaching the compressor kit onto a second one of the plurality of identical universal base units to construct a second air conditioning system of a second type.