Air conditioning in a Cali ... well, depends how hot the ambient temperature is and how cool you need it to be to sleep well. I survived 30c quite comfortably with roof raised, all the vents open. The vehicle cooked during the day but I wasn't in it, the table in the side door and chairs in the tailgate meant I lived outside during the day unless I was moving in which case the vehicle AC was brilliant.
Heating in a Cali ... it comes with an inbuilt furnace called the auxiliary heater. I was in minus 5 three weeks ago and slept quite comfortably with the heating occasionally bursting into life on the very lowest setting a few times during the night. It also comes with a wholly shamelessly decadent remote control which means you can wake up in total ice, press a button, snuggle down for ten minutes then get up into something all warm and friendly and get the kettle on.
If on hook up take an electric heater with you, the auxiliary does come complete with a noisy ticking, which after a while blends into the background, but just in case you are of sensitive and irritable disposition you can ameliorate by using someone elses electricity to keep you a warm and happy bunny ...
but who wants to be anything but self-sufficient in a cali? It takes away that wonderful, glorious smug feeling of up being totally independent, free to travel and stop wherever, I can survive without anyone's help - or electricity.