When I am running my A/C it seems like my alternator isn't keeping up.  If I stop at a traffic light, my radio will turn off.  Also, the battery will be weak and  the next time that I try to start it.  It is fine, without the A/C on. 

I checked it with my voltmeter and it puts out about 14V at idle with no A/C but drops to about 12.4V with the A/C on.

   Do you think that the alternator is bad?  Bad Ground?  or something else?

Thanks

The stock alternator is not capable of keeping up, time to upgrade to a much better and far cheaper Delco Remey 12si alternator, 25$ for a Trail Tough alternator mounting bracket and 50$ for a rebuilt alternator at NAPA.

Does your idle pick up when your AC is turned on?  If not your fast idle might not be working correctly.  Your battery might also be on it's last legs, it should be able to run your radio and other devices without an issue while your at a light.

The idle doesn't increase, when the A/C is on.  What controls that and where is it located?

ya know my 1994 sidekick had the yellow wire for the idle up on the power steering and for the a.c. and it went to the ecm but the ecm did not have the circut inside of it for it to do anything, maybe they were getting ready for the next years model?

Regardless of the idle not going to high idle, the alternator voltage output is dropping significantly,  sure there may be a issue with the idle up feature, but I really doubt that is the cause of your issues. The alternator should stay well above 12.4vdc at idle. It only takes a little time to pull the alternator and go to a Autozone/NAPA/Pep Boys and have it checked. It wouldnt hurt to also double check the grounds for corrosion/dirt etc.

A friend of mine just replaced his lower pulley on the crank because the rubber on the balancer was slipping on the pulley and caused it to over heat, but the same belt that ran the water pump runs the alternator, it was only two hundred and seventy six dollars.

A friend of mine just replaced his lower pulley on the crank because the rubber on the balancer was slipping on the pulley and caused it to over heat, but the same belt that ran the water pump runs the alternator, it was only two hundred and seventy six dollars.

I would have sold him a good used one for half of that.

I just had a similar problem, with an easy fix. Maybe worth checking into before you spend any money.

The lower pivot bolts came loose and would cause it to charge some times and then not some times. Good luck with it!

I replaced the end of the negative battery cable because it wasn't clamping on the battery terminal tight and I added an extra ground cable to make sure that it was getting a good ground.  This seems to have done the trick.

You can never have to many ground wires.