Nobody knows how the ECU (engine or BCU) is programmed for A/C. It might just be a more aggressive idle setting, but it's more likely to be more sophisticated than that.
But if you think air con simply be added to a none aircon car, think again. The heater unit has to be replaced (1) Try finding one. (2) You have to remove the front doors and extract the structural frame hidden by the plastic dash before you can get the heater out of the car. You'll probably have to mess about with steering pedals and brake levers as well.