If you find yourself parked, i.e. stuck in your car with the air conditioning on, the traffic police could still fine you.
The situation is different when driving. The air conditioning can be left on all the time. This law was created to limit pollution from cars as much as possible , which, when stationary, should keep the engine running to use the air conditioning.
In fact, it is now known that the ‘endothermic’ engine of cars, especially the older ones, releases large quantities of CO2 into the atmosphere , and for this reason it must be turned off when not in motion.