[QUOTE=larry perkins;1505261]on the blue temp sensor on the head(3 from rear) even though it is a varable value from about 3k ohm down to about 300 when hot,if you unplug it (open ckt) the aux fan should run at high speed,so this test does bypass the low speed ckt for a test of the high speed. of course if it dont run then you have to trouble shoot.>>>

You have the test correct, but it does not by-pass low speed circuit..has nothing to do w/low speed circuit.
The high fan on the thermister type sensors is controlled by the A/C Control panel circuitry..which defaults if it sees an open circuit in the thermistor or wiring leading to/from the sensor...that is an engine coolant temp saftey design in the CP circuitry in case the sensor goes out, the engine still has high Fan..all is you are doing when you do the high fan test by unplugging the termistor is you are making the Panel see an open sensor.wiring and causing the CP to go into fan default. Nothing to do w/low fans circuit.

One can also change the cut-in of the termistor by bridging it with a parallel
resistor to change its Total R factor by a few degrees . Many do this simple mod just to have the High Fan come in at around 100C, vs the factory spec of 105/107... this works well for temperate climate loactioned cars