I do not believe that sw is a thermistor sw , but rather just a temp on/off sw.
The resistor will only work on a thermistor sensor because it changes the
resistance of the sensor [ with parellel resistance] in relation to temp.
This new resistance just puts the sensors values out of spec enough to create an earlier cut-in of the fan circuit.
Out of calibration, but to ones own liking...

An interesting side note to this..
The only reason this resistor bridging will work on these thermistor sensors is b/c the sensors are of the Negative Temp Coefficient design.. meaning , as the temp increases, the resistance decreases.. and when one puts two or more resistors together in parellel, the total resistance also decreases [ei. is always less than any single resistor]. So , you now can change the resistance value of a sensor to have less resistance at a lower temp than the original resistance at that same temp, thereby changing the values of the sensor and allowing for lower temp activation of the fans.
Many think that this fools the control module , but the control mod just works like it was designed .. it is the upsetting of the relationship of temp/resistance specs of the sensor that have been changed/fooled.