Headlights dim when A/C is turned on to high setting

INMYHEART28

MEMBER
2010 HYUNDAI ELANTRA
4,700 MILES

My headlights were going dim when the rear window defog was put on or the air was put on high. I took it to the dealer. They confirmed my issue and according to my repair ticket "With loads on only charging at 12.8V. Also inspected and found ground cable for battery starting to come undone and corrodded. Defective ground cable caused altonater to stop charging. Replaced altonater and ground cable for battery. Rechecked charging system. Charging at 13.6V at idle with loads on." However the lights still dim somewhat when the air conditioning is placed on high. Is this a problem? What should be done now?

Saturday, November 17th, 2012 AT 1:44 AM

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

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.

https://www.2carpros.com/articles/how-to-check-a-car-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

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