Our Fantastic Fans started acting up today - they would open and then after a while, in humid conditions, would close. But, there was no rain, so why was this happening? Well, it turns out that the rain sensor, a strip of pc board with etchings on it, was corroded. This pc board is designed such that when water pools on it, it shorts out
telling the fan to close. Well, ours were green with corrosion so with just a bit of humidity the circuit would complete making our fan something akin to a character in a horror movie - opening and closing at will.
The solution is to use some CLR and remove the corrosion. Now, all is good.