Quote:
Originally Posted by lmarty1359
Thanks, but can there be ANY resistance if the fan starts to run when I unplug the sensor? I thought the fan could not run until you jumped the two female connectors on the temp plug?
|
You do not understand the sensor and/or the circuit.
The sensor is a Thermistor .. not a switch...meaning the resistance of the sensor changes with the temp. [ inversely...meaning it is a Negative Coeffecient Thermistor]...NCT
So, when the Control Panel sees the sensors resistance go from high to low resistance from the sensor , it triggers the high fan....[ using a switching transistor/circuit in the CP]
BUT, if the sensor resistance is incorrect, the CP does not trigger , and if it is open, it goes into Default mode and switches ON the high fan for engine protection in case of sensor or wiring failure. When you unplugged the sensor , you are simply putting the CP into DEFAULT ON mode you then get HIGH FAN. That is how we test for high fan..we simply unplug the sensor justlike you did .That tells us that the fan circuit is working, but if it does not work at high coolant temp, we suspect a bad sensor...so, as I posted, we have to take a RESISTANCE reading at the sensor to see what is up.
This sensor is not a switched sensor as you suspect ..it is a THERMISTOR and triggers a Transistor balanced circuit at a specified Temp/Resistor value..in ithe words , it is Electronic switching, not mechanical sensor switching.
There is a temp/resistance chart for this sensor, but if you just do my test, I will tell you if the sensor is the problem.
You never jumper a thermistor sensor, you simply unplug it and ohm value it.