<<If the switch contacts do not close at all after the a/c has been on for a couple of minutes (no resistance reading), you can be sure the switch is the problem.
The only way to truely check the sw is with gauges on the High side for sw spec comparision..
There are times when the fan is not called for [ low thermal load conditions , ie -low temp/humidity] , so do not expect a fan under these conditions.
The fan is there as an AID to high head pressure of the condensor [ a/c high-side] and simply comes to the rescue
when more airflow is needed..usually at stop/idle on hot ambient days. Once the car is moving , the air now crossing the condensor will limit the high side pressure and the sw will open and turn the AUX fan OFF...
So, one can see, if the freon level is not COMPLETELY charged, the system will never reach a high side sw cut-in spec for aux fan...A trained eye can see this in the eye-sight and a trained hand can feel the temp on the condensor in and out lines , but for exact sw cut-in/out pressure comparisions, gauges are your next step for proper diagnosis..