Abstract: A control apparatus for an air conditioning system has an outdoor unit with a compressor, a condenser and a plurality of motorized valves installed to a plurality of branch pipings. A plurality of indoor units having, a plurality of indoor thermoswitches, a microcomputer, and a drive circuit for driving the motorized valves according to the output from the microcomputer are also provided for the control apparatus. The microcomputer counts the number of indoor units required for operation by receiving the output from the indoor thermoswitch. The microcomputer also controls the opening of the motorized valves by predetermined opening steps, according to the result of the counting and with reference to an opening table. The opening table relates the number of indoor units required for operation with the opening of each of the motorized valves. The control apparatus thus permits an optimum distribution of refrigerant to the indoor units to be set quickly.