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Alternator question

I’m thinking my alternator is dying, but I’m not sure

*Car is sometimes hard to start and cranks slow

*Headlights at night are somewhat dim

*Various idiot lights coming on intermittently on dash - they change up according to mood, apparently, and most will go off when radio is turned off

*Radio not holding pre-sets and clock not keeping correct time

Now, if this indicates the alternator, can the alternator also cause the air conditioning to not get cold? I’m wondering if it might be keeping the compressor from working and therefore no cold air? Maybe?

Thanks for all your help guys!! I am pretty clueless when it comes to cars and what needs repairing, so you all are an extremely valuable asset to me.

I appreciate YOU!!

The most important thing to convey when asking a question such as this is, what type of vehicle are you talking about?


Start the car and then pull the negative cable off the battery. If the alternator is OK, the thing will keep running. This sounds more like an old generator.

If the AC is affected, I would check the tension on the belt.

The alternator may be going bad but other things can also make the lights dim and slow cranking. Make sure the alternator belt is good and snug along with making sure the battery connections are very clean and snug fit to the battery post. The alternator voltage should be between 13.5 and 14.8 volts while the engine is running and idling fairly high. You may want to have a shop check the charging system out so you will know how you stand. The battery could be weak also.

As far as the AC and the memory problems you should make sure the fuses are ok. There may be a bad fuse causing those problems. The alternator isn’t going to cause those problems.

I don’t recommend you remove any connection to the battery while the engine is running due to the possible damage that can be caused to the electronics in todays vehicles from voltage spikes coming from the alternator if the battery isn’t connected. Some folks have gotten away with doing this but any good shop will warn you not to do that. In the days when generators were being used in cars it was ok to do, but not now.

You can, and should, have both the alternator and the battery tested. Most auto parts stores will do this free.

AC that doesn’t get cold enough is a separate problem.

Have the battery and alternator tested. It sound like one or both is nearing the end of its life.

You DO NOT want to remove a battery connection on a vehicle that’s running. This can cause a voltage surge throughout the vehicles electricals, damaging computers and modules.

You use to be able to do this before they started putting computers in vehicles.


I wholeheartedly agree with Tester. DO NOT remove the battery connection on a vehicle that is running. Doing so can, and may very likely, do some serious electrical damage.

Okay, first, it’s a 97 Chevy Cavalier RS Coupe. It’s got several issues and yes, I bought it this way. Not deliberately. It’s my caveat emptor lesson in life! So I asked the guys at Kragen how to tell whether it’s the battery or the alternator. They said, we’ll test the battery for you. (BTW, this is after it wouldn’t start and had to be jumped.) The test said bad cell, zero charge. I went to Wal-Mart (where the orig battery is from) and bought a new battery. Installed it, and all seemed great! Drove to work this morning, all is still great. (no cold a/c, but who cares) I drive home from work and notice that the battery light (which did NOT come on previously) is now coming on while I’m going fast (freeway) and goes off if I get down to under 25mph. I made a stop, it started back up just fine. I’m driving the freeway for about 20 minutes and the temp gauge and speedo go to zero (like the car’s off) and then it starts acting like it’s missing. I take the next exit and it completely dies. Won’t start, nothing. I guess I needed a battery AND an alternator.

Okay, so I’m buying an alternator. Is it something that someone (me) with reasonable intelligence can follow taking the old one off and be able to put the new one on? I should be able to borrow whatever tools I’ll need (what WOULD I need?) and how long do you think it would take, if you think I’m capable.


GROUNDS…Yes I’m Shouting…My wife’s '99 Malibu did nothing more than “my clock is at the wrong time” (that is -reset) from her. The cure was an independent ground wire…no further problems.

Let me clarify what this poster is trying to tell you, because I think he is right. You need to make sure that the negative battery cable is making good contact at both ends, that is at the battery and at the block where it is bolted to. In addition, there will be a small wire going from the terminal to the body near the battery.

Also, there will be two or three ground cables running from the block to the cars body. These are usually small braided flat uninsulated wires, about a 1/4" wide. One of them should be going from the front of the engine, near the valve cover over to the body by the front motor mount or upper strut mount.

If you can’t find any of these wires, make one. Use at least a 10 ga copper wire, attach terminals and run from any convenient bolt on top of the engine to any convenient bolt on the firewall or anywhere in the engine compartment.

Then check for any loose connections on the alternator.

Cavaliers of the vintage the OP has have their main body ground at the metal battery tray and I have seen them completely break off (and we know the kind of corrosion present in the battery tray).

Thank you all sooo much! Prior to some of your responses, I purchased an alternator and (believe it or not!) installed it ALMOST completely by myself! That was somewhat of a pain in the ass, but no doubt due to my ignorance of the whole thing. I had been told that there was a small square hole that I needed to use a 3/8" ratchet in (for the belt tensioner) and I could not find that. I had a friend (slightly more knowledgeable than myself, but he’s not a car person) come help me with the tensioner part. And voila! All is well (for now). Aside from the various annoying lines and tubes and things in my way, and not having the one perfect size socket, and of course the tensioner issue, it was an absolute blast!! I mostly had fun, and I love learning new things, but the real prize was when it started right up and all things seemed to be happily performing their magnificent jobs! Thank you all again, so VERY, VERY much!!! Hope to talk with you again soon! (Hmmm… not too soon. That only means there’s another thing wrong with my car! lOL!!)

Good work SS and thanks for the update. Hope that takes care of the trouble. You may want to consider taking the vehicle to a shop and have them do a load test on the charging system just to verify everything is in good shape. That will test the alternator and the battery along with the with wiring between them.

Thanks Cougar! I’ll do that. It just rolled over to 150K miles and I need to get that maintenance done, so I’ll have them do the load test at that time. Thanks again for all your help!

You’re welcome SS.