[BNM] aircon units fitting

[Simon Early]

Dumb question follows:
with a split aircon unit (ie separate compressor fitted outside) is it
important to put the compressor somewhere out of direct sunlight, or doesnt
it matters?

Presumably if it is trying to exhaust hot air it would be more
efficient/better if it was doing it somewhere cool?

funny thing is I have seen them mounted on walls/ceilings in full exposure
to the sun, so wheres best to situate them?
cheers,
s./