Voltage drop with AC on

[JamesHatch]

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?

 

[lawsoncl]

I'm going to bet the belt is slipping. Don't guess on the tension. Just pickup a Krikit II belt tension gauge for $12 at Napa and set it correctly.

Per the FSM, a new belt gets between 180lbs and 200lbs. A used belt gets 140lbs to 160lbs. Used belt is defined as one that has been run for 15 min or longer.

 

[Saudade]

What lawsoncl said.

Also, did you measure voltage at the battery with a voltmeter or are you going by the dash gauge? Does it vary with ac on and different fan speeds?

 

[RCP Phx]

It sounds like a voltage drop issue. Check all your cables for any corrosion and lube the connections. Might also be a good time to test the battery as that's also a sign of a cell going bad.

 

[Unclewolverine]

Definitely measure with a meter at the battery, my dash gauge is off by 2-3 volts.

 

[JamesHatch]

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

 

[Saudade]

Glad you fixed it!