When icons fail to deliver
Icons are important elements of user interfaces. They can e.g.
- Save space on toolbars and buttons,
- Speed up recognition compared to text once learned (for instance icons based on convention such as a cogwheel for “settings”) and
- Reduce the need for additional textual explanation (e.g. icons representing the result of an action, like the banding of rows in a table editor).
A bus air-fan icon pair not up to the task
However, sometimes icons fail to deliver and I came across such an example while riding the bus.
Above the seat there was an air-fan:

As you can see, there were two icons referring to the air-fan being fully open and fully closed, respectively. Just by looking at the icons what do you think means what? (read on to get the answer)
My proposed icon redesigns
The problem is that icon pair isn’t sufficiently easy to distinguish. A better design would have been anything that would help make the distinction more clear.
2 examples of redesigns:

By the way: In the original design, the full white icon meant fully closed – I think, but I really can’t remember…