I CAN'T MAKE SENSE OF THE MANUAL!
Understandable. These things are never well written, are they? Try and take it as literally as you can.
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First things first. The controls for the fan are on top of the stairs. To begin with, set the fan to off (o), speed to low (L) and direction to anticlockwise (left).
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Switching from low to high, high to low and low to high would mean tapping the speed dial three times.
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Switching the direction from AC to C three times would mean AC-C, C-AC, AC-C, C-AC, AC-C. So tap the directional switch 5 times.
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Now, to repeat the speed control steps as before, you need to first set the speed to L again. So tap the speed dial 4 times.
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That's it. Turn the fan on. You are in diagnostic mode.
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Now that you are, the fan needs to turn anticlockwise to create a downdraft, so tap the directional control switch once more.
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And voila. Fan destroyed. Go downstairs to see what you accomplished.