If you look at any air con that actually cools the air, you will see it takes a lot of power to run. Far more than you can get from the 12v battery. So you either try to tap in to the traction battery and accept reduced range or you look at a simple water sprat fan system.
The Twizy was designed to pass air round the driver and keep them dry. So an alternative is to add some air deflectors to get the air flowing inside.
Traditional air con only really works on a sealed box which the Twizy certainly isn't.