i had the car for a 1 year and now this small fan 1/2 inch between the lights and above the mirror is making noise ,what is the reason for this fan 91 500 sl can i disconnect it?

 

you dont want to just disconnect it, as that fan is for the interior temp sensor for the climate control.

 

I agree, it's a fan to draw air from the cabin in over the temperature sensor. You cannot replace just the fan you need to replace the whole unit which costs upwards of $300. You might find some very careful dismantling and cleaning might solve the problem.