A/C causing alternator no charge.

Unique problem I've never experienced before.

99 4.0 aw4

Symptom
Driving down street "check gauges" light comes on.
Voltage gauge reads minimum.
Turn off jeep,Turn off AC, restart and Everything returns to normal.

Troubleshooting results so far:
1. Turn hvac to vent, blower on high. Result: Normal voltage
2. Turn AC on max, blower on high. Result: voltage drops out slowly.
3. Turn AC on, unplug AUX fan, blower on high. Result:Voltage drops out slowly
4. Turn AC on, wait for Aux fan to come on, unplug compressor. Result: normal operation.
5. Rev engine as voltage is dropping, zero change in voltage.

I can hear a noise from the alternator as the AC clutch engages.

The belt is tight.

I have now replaced the alternator. I think this may have solved the problem, The alternator was only a month old though.

I still don't understand how the AC clutch coil manifested an issue, while the aux fan, which draws way more amperage, didn't show any issue.


Unless, perhaps the rotating internals of the compressor were enough to excite the field sensor in an improperly shielded rebuilt alternator enough for the PCM to tell the system not to charge :dunno: