What determines the duty cycle of the A/C compressor?

[LtNoogie]

Since there is no real temperature setting like higher end cars, I was wondering what determines how long the compressor stays engaged or not?

I've always maintained, correctly or incorrectly, that the compressor duty cycle is preset at the factory. The temp gauge on our Yaris allows us to mix warm air in with the cold to make the air more comfortable.

The reason I ask is that on balmy nights, I like to cruise the boulevards with my windows down but with the A/C on. I like the cool air on my face but being able to see and hear the action on the streets.

My GF says, I'm wasting energy by doing this. I tell her that the A/C uses the same energy all the time that it is turned on whether the fan is set to fresh air or recirc or whether or not we roll up or down our windows.

Thanks