On Wednesday, April 11, 2018 at 9:24:42 PM UTC+10, Scott wrote:
Maybe pushing my luck here (but I am an opportunist). Any ideas why
the aircon light (and I assume the aircon) on a Nissan MIcra should
default to 'on' when the ignition is turned on rather than to 'off',
as I would expect?

If it is so it is a dumb design. A/C on in any car takes a fair bit of drive power, the car slows down.
In a car like Nissan Micra which I think is of 1600 or 1400 cc it would mean engine would struggle to move with even an additional passenger on board. I would investigate, make it default A/C +off condition