Engine control apparatus of vehicle having air conditioner

An engine control apparatus of a vehicle comprises an air conditioner with a variable displacement compressor (104). The pressure difference measured between two monitoring points in a refrigeration circuit represents the compressor displacement. The compressor is controlled by a control valve (109), which operates based on the pressure difference between the discharge chamber (23) and the high pressure conduit (40). A controller compares the temperature of the passenger compartment with a temperature setting. If they differ, the controller determines a target pressure difference for the control valve. The controller computes the compressor torque based on the target pressure difference signal. The controller determines a target engine torque based on the compressor torque and controls the engine based on the target engine torque.