^^ good warning to keep in mind!
We usually use position 4 to "force" the A/C on to do the "quick check" of fan operation, without that you would need to look to see if the compressor is cycling on to know if it's actually operating... (wouldn't necessarily turn on in cooler weather)
No operation in 4 often traces down to the switch, but electrical testing is needed to confirm that instead of throwing parts at the issue. One side of the fan connector gets power, the other grounds through the resistor pack & the switch to turn it on. That's why when folks check for power at the resistor connection they don't see any! So a multimeter is needed to check the circuit.