The engine fan sensor is cylinderical and is screwed into the engine behind the oil cap.
Another way to test it is as 16VAlex mentioned.You pull the connector off the sensor and use a piece of wire to create a short on the connector.
My mech took about 25 minutes to replace the electromagnetic clutch on my car (he's GOOD, FAST and CHEAP).No hoist required.
He worked from the front of the car and had to loosen the serpentine belt.Then he took off the fan shroud, blades, etc before gaining access to the clutch in front of the water pump.
I replaced the aux fan on my kid bro's 190e and it took me about 2 hours.I had to do some modification to the mounting brackets coz the fan came from an earlier model 190e and had slightly different mountings.
I believe a good tech would take about half an hour to do it.
Good luck with the test.
Babybenz 1991 190e 1.8