Currently, there is no way to cool (or heat) the cabin on the ground without the APU running. While it doesn't affect how I fly the aircraft, these little things add to the realism and sense of preparing the ship for a long flight with passengers and your competitors have them added in. Getting the cabin ready is an important part of the pre-flight and it would be nice to be able to do this without starting the APU as happens most of the time in real life. I would love to see the following added in the future.
1.) External Pneumatic Air (High Pressure Start Cart) - This was available in the MSFS A310, so I'm curious why it is excluded here in the A300. j
2.) External Pre-Conditioned Air - This was not available in either the MSFS A310 nor the A300, but as it is the most common way to condition an aircraft at the gate in real-life, I really think it should be added as an option.
Please see the following photo as a simple reference to show why these are an important part of the pre-flight process.