See point 8 in original posting:
Rest assured, those of us in the small office at the pointy end are usually sweating too. Many aircraft are not able to condition the cabin air effectively until both engines are running, and most cannot provide any air-flow to the conditioning packs during the engine starting sequence, as it is all used for accelerating the engine core.
This criticism should be addressed to the aircraft manufacturers who produce poorly thought-out products, the handling companies at airports who do not keep a sufficient number of ground air conditioning carts available, the airlines who buy the aircraft and don't insist on the carts being supplied, and the passengers who are producing the heat in the first place (this last is a small funny, OK?).
Please don't blame the driver - he's often doing all he can.....