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The fan not blowing on any speed but high is caused by a burnt blower resister. The resister is located in the blower case. The sensor refereed to,is the Thermistor or duct
sensor. To replace the duct sensor the evaporator will have to be removed.The sensor
is mounted between the fins of the evaporator. To verify that the sensor is bad before removing evap. just plug in the new sensor.
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Here are the locations