Switzerland
Not a place you think of as hot what with all that snow etc. yet...
Zurich early to mid afternoon in summer 30 degrees was not unusual and
they certainly used to ban the use of APU (noise reduction) as briefed earlier on this thread - 20 mins before departure - close to the time passengers (SLF) arrived.
I knew a captain who used to regularly close blinds, assisting the crew on turnaround (also used to wet the tea on occasion), on the sunward side and also ensure all the normal air vents were and open pointed all in the same direction. It just about kept the cabin at a similar temperature to that of arrival.
Once the SLF had embarked their body heat and the, now open to sunlight, windows ensured a significant increase in temperature.
I've been there, seen it, experienced it - blinds help even if in only a small way.
R.