Engine driven air conditioner and control method therefor

In an engine driving type air conditioner having a bypass valve for returning a part of refrigerant discharged from a compressor to the suction side of the compressor, when an engine is stopped, the bypass valve is closed and the pressure difference between both the entrance and exit sides of the bypass valve is detected in a predetermined time after the bypass valve is closed. It is judged whether the pressure difference thus detected is within a predetermined range, thereby judging whether the bypass valve is open-locked. Thereafter, the bypass valve is opened again, and variation degree of the pressure difference during valve close control is compared with variation degree of the pressure difference during valve open control, and it is judged whether the comparison result is within a predetermined range, thereby judging whether the bypass valve is close-locked.