The aux fan does have a coolant temp sensor for high speed when coolant gets to 105C, BUT , that has NOTHING to do with the low fan curcuit, which is refrigerant a/c pressure activated. This sw is on the drier/reciever near the driver headlamp. It has a pigtail on it and you can jumper the feed wires ..that will [should] activate the LOW speed aux fan...which is what should happen under thermal heat load when there is enough freon/pressure on the systems high side [ condenser].. all the fan does is helps keep the high pressure in check at high load to aid in cooling and not let the pressure get so high that it kicks out the compressor...that is why it does not run all the time [ as in low thermal load conditions]

The confusion comes from many cars being wired to have fan on whenever a/c system is on .. not on this chassis..it is an AUXILLARY fan...meaning just that.