I was checking if there were any voltage drops with the new sound system I had to put in with the music up and to my surprise the music didn’t make the voltage drop at all. The moment I put the ac on it goes from 14.2 to 13 volts and stays there. This is all at idle, without pressing the gas and testing at the battery terminals. I just recently replaced the alternator with a new (not rebuilt) duralast gold alternator. Curious if everyone else’s does this as well or is this alternator weak. Can someone please check their GS with AC on for me and tell me what voltages it reads at. Thank you!!

 

I never measure it, but I know alternator output voltage/current follow engine speed change. I personally doubt the alternator might have less power than your factory one. The only problem you have would be less charging current.

 

I think it has more power it had a test sheet and says it outputs like 138 amps or something. But I’m just wondering if being parked not revving the engine is it normal to drop to 13 with ac on. I thought the alternator would make it go back up to 14 but maybe not when parked.

less charging current like to charge the battery ?

 

I have a brand new Pure Energy alt and new Duracell 24F battery. Checked mine this morning. 14 with or without AC.

 

The alternator output shouldn’t be effected by the ac compressor. It sounds like you have a serpentine belt that is slipping when the AC compressor is engaged. Either the belt is worn out and not getting good traction or your tensioner is worn out and not put enough pressure on the belt to keep it tight. I would replace both if you haven’t already replaced one of them?

 

Thank you for checking! That is without pressing the gas while idling right? Also was this a cold start? Because I know when engine warming up the RPMS are higher. I tested when the car was warm already.

 

maybe that explains the slight whining noise I would hear sometimes. Are you 100% sure it can’t be the alternator? Maybe the voltage regulator isn’t good or something. I had no idea a serpentine belt can affect the voltage. I do know the infamous serpentine belt squeaking sound and I’m not hearing that. The tensioner sounds like it could be the culprit since that can fit differently after I put the duralast alternator compared to the previous OEM one right? I THINK the previous owner did the serpentine belt but I can’t remember. Is the tensioner a big job?

 

Neither are big jobs, both pretty straight forward. The ac compressor doesn’t operate on electricity, it’s spun by the engine, so the voltage shouldn’t drop, if it does, it’s probably because the alternator isn’t rotating as quickly when the compressor comes on. Usually the compressor causes the rpm to drop by a few hundred rpms for a second until it’s able to compensate for the additional drag it puts on the engine.
You probably just need to replace your serpentine belt, but take a minute and listen carefully to the motor with the hood open before doing anything. You want to make sure there isn’t any squeaking or grinding sounds along the belts path, listen for a bad bearing or something like that. You Don’t want to have another accessory problem in the near future. A seized bearing could destroy your new belt in a split second, and u don’t want to deal with that.

 

there is that slight whining noise which I thought was the alternator itself. I can start with the serpentine belt since I remember that being an easy job. Doesn’t the alternator have to come off to do the pulley or tensioner? Thought I read that

 

The tensioner itself is actually bolted to back behind the middle timing cover, no need to take the alternator off (as far as I know and saw). I painted my timing belt covers blue anyhow (the valve covers are also painted that), and I changed my serpentine belt with help from my brother (holding the ratchet while I take the belt off and put the new one on) in literally less than a minute.

 

The tensioner has a reverse threaded 14mm bolt on it, put a good breaker bar in it and you can swing at to the max position and that’ll give u just enough slack to pull the old belt and replace it with a new one.
Instead of buying new pulleys which can be kinda speedy, you can actually replace the bearings in them for about $5 each, there is 2-3 that end up needing to be replaced overtime