This is caused by one of three things. First, and most likely the blower motor is drawing too much current on the high setting so you may have an issue with the motor or resistor. We need to perform a voltage drop on the motor and see what it is drawing. On high setting it should be around 12 volts.
The next cause is a weak alternator. The fact that it is only charging at under 14 volts at idle is low. If this is under producing then it will not produce enough voltage for the added system when the fan is on high. This means we need to load test the alternator.
Lastly we could have a wiring test. However, I suspect you have an issue with one of the other causes. Let's start with those and go from there. Thanks
Saturday, May 16th, 2020 AT 6:50 PM