The 4 cyl 190's (both the 16V and the regular 2.3) have two fans and two switches.
First, the electric fan clutch that is mounted onto the water pump is turned on by the 3-pin switch on top, front of the cyl head. This is supposed to come on at 105 C° to 110 C°.
Second, the auxiliary fan in front of the radiator is turned on by the red or green switch on the receiver drier, and most 190's were updated so that the electric fan clutch on the water pump would also come on at the same time.
These engines therefore run 10°+ cooler if the AC is on and functioning properly than if the AC is off because the first fan comes on at a much higher temp.
Of course start by checking the fuse first, then by jumping the switch for each switch, then checking the fan, relay and wiring as required....