Fan fuse causes drain on battery?

This mystery continues. The latest diagnosis is that there's a fuse, maybe blue in color and the car owner told me it was blue. When th is fuse is removed or put back in there's a fan that comes on when the engine is not running. I thought we had established that this fan auto comes on to cool the engine that has been turned off. A thermostat causes the fan to turn off. The car owner swears that one day the car started. Then the next day it would not and AAA and one other person think it is some fuse. The car is being towed to the same mechanic it visited last month. I personally know that the battery is not fully charged and only 385cca. These people are trying to cure a battery drain with a battery that is not fully charged. My idea which is not being accepted is to take the damn battery to Autozone for a free overnight charge to get the battery which is less than a year old to be as close to one hundred per cent as possible. Then monitor these out of nowhere the car won't start. 1990 Honda Accord. This suspected fuse related drawn downs only started this year the car has been in the hands of this owner for 15 years.
They keep getting AAA to replace batteries. No one should need a new battery every year. Who has an idea about this fuse and fan diagnosis

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