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!!!
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)