Voltage drop on 01 XJ

I’m having a problem with the voltage on my completely stock 01 XJ. If I turn on the AC, put the fan on high with the headlights on the voltage drops down to 12 or a little below using a multimeter. If I hit the accelerator the belt squeals until the voltage comes back to almost 14 volts, but the voltage will drop again if I release the accelerator. I experimented by using the rear window defrost instead of the headlights and the same thing happens. If I start turning things like the lights or the fan off the voltage goes right back up and the AC compressor runs fine. I also tried putting a load on without the AC and could not get the voltage to drop. This problem also happened a couple of times during the winter using defrost and rear window defrost with the fan on high and with windshield wipers on. The battery holds a charge with no problem and the alternator seems to charge at 13-14 volts, except in the above conditions. I’m not sure if it’s the alternator, AC compressor or even the belt itself. Any help would be appreciated. Thanks

i would say your belt or alternator(alt), im not sure if the regulator is exterior on that alt.

I the belt looks shinny on the inside, the its time to change belt.

There are places that will test your alt for free.

Sounds like your belt is slipping from a lack of tension. Check your belt for glazing or cracking as it may need replacing. Put the proper tensoin on it and the squeal should go away. The voltage drop at idle with the air on is normal. You r alternator is not designed to charge at idle, it merely maintains at that speed. Once over 1000 -1200 rpm the alternator will have enough speed to charge the system and meet the increased demands.

Have the system tested with a proper tester. AutoZone does it for free.

If it does say bad alternator, check the belt condition and tension first.

RandyD71 said:

Sounds like your belt is slipping from a lack of tension. Check your belt for glazing or cracking as it may need replacing. Put the proper tension on it and the squeal should go away.

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Thanks for the responses. I went to Autozone on the way home form work and the battery and alternator both tested fine. I will replace the belt tomorrow and see if that solves the problem.

It don't charge much a idle, that is why the Police version has a Idle override switch. 12v at idle is normal with everything running.

I had a few extra minutes after my last post, so I went out and just tightened the belt...that was the problem...no more squeal! :thumbup: Voltage still drops at idle, but goes right back up while moving. I only questioned it because my TJ's voltage doesn't seem to drop under the same conditions like the XJ does.
Thanks again