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Discussion Starter · #1 ·
My 1999 XJ has started having the battery voltage (as viewed on the dash) hovering between 11-14 volts in a seemingly random manner with the AC on. It does not do this with the heat running. My belt are probably tight enough, could be slightly tighter but doesn’t squeak ever. With the AC off, everything behaves perfectly normal. What could it be?
 

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Your A/C compressor has a magnetic clutch that is engaged when the A/C is on. The load of the A/C compressor on the engine, along with the additional Amps needed may be causing this fluctuation. Check your battery terminals and make sure they are clean. Check and clean your grounds. How many miles? How old are your battery and alternator?
 

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Discussion Starter · #3 ·
My 1999 XJ has started having the battery voltage (as viewed on the dash) hovering between 11-14 volts in a seemingly random manner with the AC on. It does not do this with the heat running. My belt are probably tight enough, could be slightly tighter but doesn’t squeak ever. With the AC off, everything behaves perfectly normal. What could it be?
UPDATE: the next day, the battery voltage would not read above 12v with the ac on or off. Replaced alternator and issue was solved :)
 

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Glad everything is ok now. The XJ has a funky electrical system from the factory. I had all sorts of weird voltage readings on the factory gauge, so much so I installed an aftermarket gauge and it read differently from the factory gauge. Solved the issue by cleaning all my grounds and making new heavy duty cables for my battery and alternator. Both my volt meters have read the same since then. Dirt grounds on an XJ cause no end of weird electrical problems and it's a good idea to clean them all on any recently purchased XJ.
 
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