Pulling the connector off the high pressure sw will not get you an aux fan...you have to jumper the sw.
And if you have aux fan by grounding the sw, then you do not have a bad fan motor ground ..if you did , it would not run , regardless of the sensor.
The sensors are on the relays primary side . Not on the load side.
To test the fans, bring 12v pos from bat over to each side of the pre-resistor, one at a time.. the side with R15 in Series is low speed , the other is high speed . That will test fan motors integrity and ground , along with R15 speed resistor. If yes, then problem is upstream of R15.
Suspect for no fan w/ac is low refrigerant b/c you claim fan activation with high side sw grounding..........

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A Dalton