PURPOSE: To improve comfortableness, by heightening the rotational frequency of an indoor blower when a relatively high temperature is set during cooling, to increase the quantity of sent air which would conventionally decrease.

CONSTITUTION: When the quantity of air passing through a hot water heater 17 has exceeded a prescribed value, a relay 11 is put into operation by a damper position detecting switch 13 to short-circuit a speed control resistor 8 to heighten the terminal voltage of an indoor blower motor 2. Consequently, the rotational frequency of the motor is increased to augment the quantity of air to compensate for the loss due to the passing through the hot water heater 17. According to this constitution, the time that it takes to reach a desired cooling temperature is not lengthened and uncomfortableness is prevented from being caused by the decrease in the quantity of air.