With my '96, if the air conditioning is running and the M4 auxiliary fan doesn't start when needed, the high-side pressure and temperature very quickly raise to higher levels than they should, and the engine coolant temperature increases as well, although that stays under 100C.

The key should be in position 2 for the fan test. The engine can be running or not. I use that test while driving, if I want some extra cooling for the engine.

My car doesn't need the auxiliary fan at all without the air conditioning running. With it, the fan is essential.