A little background on the Jeep and the electrical system. It is a 2001 XJ 4.0 4x4 Limited. I have replaced all the power and ground wires with the ultimate cable kit from k2 suspension which is all 2 gauge wire I believe. The alternator died a few months ago and I replaced this with a new unit. It is a 117 amp I believe. I have a Kenwood head unit, 4 speakers and sub, two amps. One is a monoblock powering my sub with about 250w and the other is a 4 channel that powers my speakers with a max of 300w rms total. The sub and speaker amps are on a distribution block with 4 gauge from the battery and 8 gauge from the distro to the amps. Grounded from a solid distro block to the frame under the rear seat. I have been informed by a mechanic my ac compressor is weak.

Now to the issue at hand. If I turn my ac on while driving, my voltage will fluctuate at idle. Sometimes dropping all the way to 9 or 10v on the dash. If the ac is off, this it will fluctuate from 13-14. When under higher rpm, it does not seem to drop. I got done with a long drive yesterday (about 210 miles) and when I turned the XJ off, it was like I lost all voltage. My door locks would not work. I left the Jeep alone for a bit, turned the key to read voltage and it was reading 10, but it starts right up when I turn the key. I checked the battery when this issue started and I had around high 12s or maybe low 13s I believe with the jeep not running and mid 13s with the jeep running. I tried to take the voltage at the battery when it dropped, but didnt see any drop on the battery. I am kinda lost as to why this is happening.

I have two current ideas as to why. It is currently hotter than the sun in Florida, so maybe the temp sensor under the battery is reading a high temp and causing the battery to limit the voltage being given to it by the alternator. The other idea is that the ac compressor is so weak it is pulling a very high load causing the voltage to drop. Any ideas or troubleshooting tips are appreciated.

Thank you

 

The battery gauge is not (always) reliable and can't be trusted when you try to troubleshoot.
Your grounds clean too?
And how old is the battery itself?

Also, came across this below interesting re compressor ground.

https://www.cherokeeforum.com/f2/vol...ping-c-226096/

 

Grounds are clean, wire wheeled them while I was doing the cable upgrade not too long ago. Battery ill have to check but id say probably 2 or 3 years old at this point.

I may have to look into that compressor ground, that seems like an interesting write up

 

I thought so too
Let us know

 

Only with the A/C on or the blower on in general?

If you're battery reads good when tested directly my guess would be the blower motor ground and or the dash ground needs cleaning.

 

I doubt it truly dropping to 9 without any running issues