abe72 Posted September 4, 2014 Share Posted September 4, 2014 Hello all, This past weekend while using the AC my GEN light turned on, when I turned off the AC the light also turned off. Is this a alternator problem or something else? Thank you for your help in advance, Abe Quote Link to comment Share on other sites More sharing options...
72-CLASSIC_RIDE Posted September 4, 2014 Share Posted September 4, 2014 Not the most knowledgeable here but I would 1st check the Alternator to see if it is putting out the voltage required and then also the battery. Those are the 2 places I would focus on (alternator going bad or a weak battery). That draw with air conditioner on may be the tell tale sign that charging system is weak as fore mentioned. Doug Quote Link to comment Share on other sites More sharing options...
stangeba Posted September 5, 2014 Share Posted September 5, 2014 Abe, Has anything changed like replaced something in the dash or changed something under the hood. My first thought was a very loose fan belt, but that's probably not it. Is this light on at different engine speeds (idle as well as driving) and is it bright? Many places will test your alternator for free if you bring it in. I strongly believe in repairing your alternator vs just throwing in a "rebuilt" one. Bruce Quote Link to comment Share on other sites More sharing options...
MGD72Monte Posted September 5, 2014 Share Posted September 5, 2014 What is your voltmeter reading with AC on then off? If you don't have one in the dash, use a portable one under the hood. Quote Link to comment Share on other sites More sharing options...
Rob Peters Posted September 5, 2014 Share Posted September 5, 2014 I would not rule out a loose fan belt that when compressor engages it drags it down enough to drop the voltage outside acceptable limits. Rob Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted September 5, 2014 Share Posted September 5, 2014 Voltage test with ac off than on, a quick check is disconnect battery with car running if engine dies alt isnt charging at all but not the best way to check. Do you have external regulator or internal? has it been changed or still factory? Quote Link to comment Share on other sites More sharing options...
abe72 Posted September 5, 2014 Author Share Posted September 5, 2014 Thank you all for your advise. I just had the engine rebuilt, but had used the AC before without issues. The light turns on at high rpms and idle. I had notice the dome light "diming" at idle. I don't have a voltage meter, so I will have it checked out this weekend. I'm pretty sure the alternator is running about 63/65? amps, thinking of going with 80 amps. would that be sufficient? Quote Link to comment Share on other sites More sharing options...
MGD72Monte Posted September 6, 2014 Share Posted September 6, 2014 If you are running a basically stock set up i.e. no electric rad fan, no 50000W sound system, or other non stock current drawing system, the stock alternator should be fine. So if it is the problem, all you should need to fix is the alternator, either rebuild the existing one or get a new stock spec one. If the alternator is not the problem, getting a new or more powerful alternator will likely not help you. Good luck Quote Link to comment Share on other sites More sharing options...
72-CLASSIC_RIDE Posted September 6, 2014 Share Posted September 6, 2014 Just a long shot here but, since a recent rebuild, check your alternator belt and for tightness. It is another possibility and easily overlooked. Based on your last comment, gen light comes on at Idle and at high throttle? Are you saying at moderate speed, gen light goes out? Doug Quote Link to comment Share on other sites More sharing options...
abe72 Posted September 6, 2014 Author Share Posted September 6, 2014 Hello all, I took some of your guys advise and tighten the alternator belt a bit. Started the car and turned on everything I could, lights, radio, AC, and the GEN light did not turn on. Also,took it to a local shop had it checked and it was reading okay, charging fine. Maybe a loose belt was the problem, I'll keep an eye on it. Thank you all for your ideas and advice. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted September 6, 2014 Share Posted September 6, 2014 always check the easiest and simplest things first! Quote Link to comment Share on other sites More sharing options...
LostnFound Posted September 7, 2014 Share Posted September 7, 2014 Hopefully it was just a loose belt but your alternator may be on it's way out based on my very limited experience. Quote Link to comment Share on other sites More sharing options...
footballubet Posted September 7, 2014 Share Posted September 7, 2014 Glad it was the easy fix. Too many times we over think when diagnosing things. I see it a lot at my work. Quote Link to comment Share on other sites More sharing options...
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