PURPOSE: To permit to condition air in rooms in some combination thereof without causing the shortage of capacity by a method wherein only the dampers in one group among a plurality of groups are opened by the operation of a switch.
CONSTITUTION: A heat source machine 3, having a capacity capable of coping with the number of rooms to be air-conditioned simultaneously, is selected. Dampers 8 are controlled by the operation of a switch 13 so as to be opened fully or closed totally while four sets of dampers 8 are divided into two groups consisting of two dampers for the rooms used frequently in daytime and other two dampers for the rooms used frequently in nightime, for example. The switch 13 is provided with two select buttons for the group I and the group II and either one of them is selected in accordance with a time band or an usage. In this case, two buttons will never be brought into ON condition simultaneously and when one of the buttons is selected, the other button is released automatically through electric or mechanical operation. Accordingly, many rooms may be air-conditioned surely by the heat source machine having a small capacity.