If you don't already have air cooling ( an a/c button on the heater panel, I think) then you have a much harder task. You will need the cooler, so there's the compressor to fit, needing a new "fan belt", then the condenser, all the pipework, and the evaporator in the cabin air duct. You would probably have to fit a new set of air ducting so as to fit the evaporater in (the cooling bit - it sits in the ducting between the fan and the heating matrix). All the cabin air passes through the cooling matrix, then temperature control is done by diverting some or all of it to the heater. That's what dries the air and makes it good for demisting - cooling it drops out all the moisture, then heating it up again makes it drier.
I have no idea if the loom has the wiring you'd need or if you'd have to add in new wiring.