Abstract: When a temperature inside a vehicle cabin is higher than a temperature outside the cabin, a full cooling mode of operation is started by moving an outside/recirculated air selector door to a first position where 100% outside air will be supplied to replace the hotter inside air. When the inside temperature is lowered to substantially coincide with the outside temperature, the air selector door is shifted to a second position where the amount of outside air supply becomes 0%. As the inside temperature is further lowered to a level somewhat higher than a preset command level, the proportion of the outside air increases from 0% to a predetermined upper limit such as 30% little by little until it is fixed at 30% when the inside temperature settles at the reference temperature. A compressor is kept inoperative in the first stage of cooling operation in which the selector door is in the 100% outside air position.