How do they work? Most of time they work fine in my car but usually it goes crazy max speed even when there’s little rain, and also at lowest speed when it’s pouring rain…
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There’s a small infrared camera usually behind the center rear view mirror, it looks at a small patch to determine the rain frequency and sets the wipers accordingly, it’s up to the software to understand the speed of rain and decide what wiper setting ti use, and it’s not a very easy to code thing, so on many vehicles it can seem kinda random at moments
Many use a dedicated [rain sensor](https://www.trueblueautoglass.com/windshield-rain-sensor/) that detects rain or water on the windshield by a change in how light passes through it when water is present on the surface of the glass. Some cars use an existing full camera and image processing to identify when there is water on the windshield.
There are some drawbacks to automatic wipers, as you noted, as they may mis-judge the amount of rain/water. Further, they are usually only looking at a small part of the windshield, so if there’s a lot spray coming up from the road that is obscuring the view mostly far from the sensor, it may not trigger at all.
I find that mine work pretty well most of the time, but I occasionally have to tap the single-wipe button or turn it up/down a touch. It seems pretty good, but it’s not perfectly matched to my preferences at least.
There is a sensor usually behind you rear view mirror it detects water on the glass, it will be in the arc of one of your wiper blades so the rain is cleared from the sensor area when it wipes.
The sensors work on change rather than level and “recalibrate to zero” when the wiper clears the water.
Some systems also use the intermittent wiper rate control (the variable adjuster on your wiper control stick) as a sensitivity setting control.
It may be that you are inadvertently adjusting the sensitivity by altering the intermittent wiper control.
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