Generator question

I've been on here for a while now, and I've never heard of this happening before, so I'm really curious. Today on a short trip accross town, my generator light came on. I've been running with the AC on for about the las two months due to it being rather hot. Today the weather was nice and so I rolled down the window and shut the AC off. There was an imediate jump in voltage on the volt gauge. (I know its not that accurate, but a big jump tells me something is going on.) After driving a few blocks, the volts went up a little more, to around the 14 mark on th gauge. This tripped the light. Turning the AC back on dropped the voltage back down. What is going on here? After stopping and starting the jeep up again, it seemed to be just fine as far as volts are concerened. Aftewr I got home I checked in my FSM and it alluded to the generator's output being in some way controlled by the PCM. The FSM didn't really list anything to check, it pretty much just said either it works or it doesn't and if it doesn't, replace the generator. Any clues here? I don't want to cook the electrical system by having an overlead of volts. Thanks for any help.

1. It's an alternator, not a generator. Does essentially the same thing, but in a different manner than the old-fashioned generators used prior to about '63.

2. You may have a high resistance in the charging system, like a dirty battery cable connection. Check and clean, especially the grounds.
I'm thinking that your AC is taking more power (amps) than the alternator can deliver, so it's sucking down the battery while driving with it 'on'. When you shut off the AC, then the alternator is 'spiking' to try to recharge the battery.
The alternator will indeed burn itself out trying to charge a battery, if the amps can't get into the battery because of a bad connection.

After cleaning the connections, maybe go to a shop and have the charging system checked.

Good luck.
-Rick

A couple of further possibilities:

1. The belt is slipping when the AC engages. Don't count on it squealing. Serpentine belts often don't.

2. The AC clutch is shorted out, and though it still engages, it might be drawing too much current.

3. I'm a little confused when you note both a light and a voltmeter. Where is the voltmeter connected? The factory voltmeter will often lie, especially if you are running the fan at high speed. The voltmeter circuit is too intimate with the fan circuit. The lighter circuit is probably also suspect. Before you do anything drastic, make sure you're getting a voltmeter reading at the battery.