Cooling fan sensor location?

I have everything to do the teardown and will be ready this weekend or next. Engine was taken well care of and when pulled head out before no sludge what so ever even before that rebuild. Question though, I havde been noticing when car would start to overheat, I would kick on the a/c fort eh fans and the car would cool down quickly. I would think it would have been the opposite due to the extra power it would need to run the a/c. Still notice coolant escaping from looks like the rad cap even though replaced twice. Water is traveling so it should not be the water pump even though it's only a year old, but could be faulty but not leaking through weap holes. All hoses replaced. Heck almost everything is new, exept the block. Hopefully this block rebuild will work out.

Yes, seems like the base of the cap because there are splash marks on that area, cleaned are to make sure not mistaken but same area. Radiator is also about a year old and no cracks or damage. Maybee too much pressure in system because hoses are very tight after ong drive and while running, cannot squeeze hoses much at all. System was bled multiple times. My guess cylnder pressure. IDK. I fugured block surface has slight warp which is why i'm resurfacing.