To determine whether the problem is inside OR under hood, you must see if the pin number 10 on the "klima" relay gets a GROUND command signal from the pushbutton assembly. WITH the car running measure for battery voltage between pins # 5(power) & pin # 10, IF you have battery voltage then the problem is in the "klima" relay.
Your car doesn't have a 105/115 switch like the 1987 & earlier cars have. Your car has a blue 2 pin BLUE sensor that talks to the pushbutton & if the engine is too hot(or bad switch) the aux fans run & the GROUND command signal to pin 10 is shut off!!!

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