in value to increase the compressor pumping capacity however the output of pid block 388 is subject to limitation based on the compressor speed cs as indicated by blocks 392 and 394 with the limited duty cycle command on line 396 being supplied to a coil driver cd 398 for the capacity control valve coil 140 as with the embodiment of fig3 the pid blocks 376 and 388 preferably each incorporate an anti wind up mechanism to limit the integral component of their output when the duty cycle output of pid block 388 on line 390 approaches 0 or 100 allowing the pid outputs to increase further under such conditions is undesirable as it would tend to saturate the entire control and degrade the control performance and of course the pid functions could be replaced with other known control strategies such as fuzzy logic or neural network controls in summary this invention provides an energy efficient control method for a vehicle air conditioning system including an electrically variable capacity refrigerant compressor the system can be configured as an automatic climate control as described in the illustrated embodiment or as a manually controlled system in which the driver manipulates interface panel knobs and or levers to.