Squealing noise possible bad alternator, A/C compressor, or serpentine belt slipping?

Hello again, banging on the Alternator, the magnetic field and disconnecting the Ground are all horrible suggestions, and those guys should have never had you do any of those. The Alternator diodes can be damaged by banging on it for one. Did you take the belt off and check each pulley by hand? If there's a bearing going bad, tightening the belt will only make it worse. At this point see if there's any AC voltage ripple coming from the Alternator. Set your meter on AC volts and go from the s Post of the Alternator to battery negative. You should have a very low voltage reading, less than .5volts of AC. If the charging system dropped off when the compressor came on, then it can be the compressor starting to seize up. The belt is going to slip and squeal if something is stopping it from rotating. 12.6 is too low, the ECM controls the Alternator and it should have raised the voltage with a load like that. So take the belt off and check the pulleys. I don't remember if you have a clutch on your compressor or if it was a variable swash plate compressor.

Okay it's possible the A/C clutch is going bad as well. But with the belt off check all the other pulleys first.
It also sounds like the battery had not been fully charged up yet. You didn't drive very far.

Hello again. well, in all fairness, the banging the alternator and magnetic field came from online, today tightened up the tensioner and the squealing is less frequent, I noticed a spark on the positive battery connector and I found there was a butterfly nut that was loose I tightened it up and it started charging the battery normally over 1300 I found that when I run the AC at full at idle the charging goes down but if I run at low or medium it maintains charge. As for the compressor it hasn't seized up yet and I have never noticed it wobble or go on and off unless the refrigerant was low, I think it has a clutch. Do you think I should still take the belt off and check the belt and pulley? Do I still need to test the alternator? Thanks

A couple tests you can do is see what the voltage reading is at the battery with all the lights on and A/C on high, as well as the rear defrost, that will put a large load on the Alternator and post what the highest voltage reading you get. It should stay between 13.5 to 14.2 roughly with that much load, another test is to see how low the battery gets while cranking the engine. You can disable the fuel pump or injectors for that test so you won't get any cylinder wash with fuel. The battery shouldn't drop below 8.5-9volts. If the battery drops too low here, it's either not charged up, or possibly has some shorted cells inside, that can happen if the battery hold down clamp is too tight and squishes the battery case.

And since you found a nut that was loose you can also check from the Alternator S(positive post) to the Battery Positive post (voltage drop test) while you have the electrical system loaded and see if there is any voltage loss on that positive cable from the Alternator to the battery, ie bad connections or corroded wires. That should be less than .5volts roughly. You can do the voltage drop test on the negative side of the circuit as well, from the Alternator housing to Battery negative. With it fully loaded you will have some voltage drop, but still you don't want much. Below .5v

It wouldn't hurt to check the AC ripple as well, just set your meter on AC voltage on a low scale, below 1volt if you don't have an auto ranging meter. When it comes to AC voltage, you want less than 50mv (0.05v) There are a set of diodes inside the Alternator that rectify AC voltage to DC that the ECM can use. Once the diodes start to go bad AC ripple will increase, and banging on the Alternator is one thing that will cause them to be damaged.

Below is a scope waveform from my truck when I was testing, there you can see the swing into the negative voltage (-75.47mv) to (91.03mv) with a total of 166.5mv which is way too high. My Alternator was in bad shape, it has actually melted to positive post going to the battery. But in the waveform, you can see the diode, each hump, it's a terrible looking waveform, but this much AC voltage can damage the ECM.

Your A/C compressor does have a clutch on it, it's a magnetic clutch. So, when it's energized the magnetic field pulls the clutch in. Thats how it cycles on and off. It should cycle about every 8 seconds or so, that's a general range, it can be different depending on wear, the amount of refrigerant, pressure sensors, temperature sensors, etc.
So there's about a million things to check, just kidding, actually most of this testing is just with your meter in a couple different places and should only take a few minutes.
I know you've just done a ton of work on this van, so if the alternator voltage stays at a decent level with the AC on medium, then run it like that. Try not to stress the charging system too much, unless you get voltage readings that are completely out of range. It shouldn't be down near 12.6 with a load on it. That means the battery or alternator are not keeping up. Here's a few guides to help if you need them. Hope things go ok for you.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

https://www.2carpros.com/articles/car-battery-load-test

https://www.2carpros.com/articles/symptoms-of-a-bad-car-battery

Okay, I'll try them one at a time, otherwise it's too overwhelming, I'll let you know as soon as I get the results, thanks.

Okay, write down your voltage readings with each test.

Well, at first startup it started to recharge around 13, but as soon as I turned on the lights it started to drop below 13 and with the A/C on low it went to around 11 and then dropped to 10 and wouldn't recharge till I turned the A/C and lights off and it was very slow, so I guess I didn't have to. Test much seeing how the voltage dropped down so fast, I'm now convinced it's the alternator, good thing I proofread this I typed radiator instead of alternator that would have made no sense at all lol Anyway I ordered a replacement should receive it Wed. I guess all I can do now is wait. Thanks

Okay, did you check the voltage drop when cranking the engine over at first start up when the battery had some charge? Also, the AC voltage check? A bad battery or issue with the main positive cable from the Alternator to the battery can cause strange charging issues as well.

Let the van run for a bit to charge up the battery and then do these tests.
First put the meter on the battery and see what the voltage drops to while cranking.
Next test,
With the van running, check from the Alternator post to the positive battery post set on DC volts and see what the voltage drop is on that cable.
Then set your meter on AC volts, and check from the Alternator post to the battery negative and see how much AC ripple the Alternator is putting out with the van running.

I didn't because I'm embarrassed to say I don't know which is the alternator post is that the one that screws on and has a cover on it? Do I just pull the cover off? Also, I have another fairly new battery I can test it with, right now it's way too hot 106 here to do much, I have to wait for the right opportunity. If it turns out the alternator is still good I'll just keep the replacement as a back up in case the old one goes, I bought a replacement starter for our old motor home last year and the starter finally started to go so I had the replacement ready to go and the mechanic was over here to diagnose it said it was gone so lucky I had the one I bought. I'll let you know thanks.

Yes, you're looking for the main power wire on the Alternator that runs to the Battery positive. The first diagram is an aftermarket diagram, and it looks to be somewhat incorrect on their labelling of the Alternator 3 wire connector. So, the second (bottom) and third (top) diagrams are the OEM and go together. The fourth is the main charging wire to the Battery. The fifth is the 3-wire connector.
If the voltage is low on the current battery in the van before you start it, then you can put the other in if you want. The static voltage should be around 12.6 with the engine off.

Okay, just seeing this now, yesterday I swapped batteries a little higher CCA on this one, it had around 12.6 on it so it started right up, didn't recharge much had to give it some gas, got up to 13-ish with lights on with A/C on and its squealing still it wouldn't get past 11.50 no matter how much gas I gave it. I will try to check the alternator as soon it's cool enough, terrible heatwave here in Texas. Thanks

If that belt is squealing that much, it is slipping on one of the pulleys, so when you get a chance take it off and check each pulley by hand, 11.5 is way too low. That means there isn't enough current flowing either to charge the battery, never mind run the vehicle systems too.

Well, if I'm going to replace the alternator, I need to take the belt off so I will do that at the same time, the 11.5 is only with the A/C on full, could it be the compressor pulley? Thanks

Yeah, the belt can be slipping either on the pulley that has an issue, or the bad pulley is causing the belt to slip on the harmonic balancer and the belt is not spinning as fast as it should. You said you tightened it up, so that made the situation worse. Did the voltage get up to 13.7 to 14.2v with the AC off? You'll know what the issue is once the belts off. If you feel the need to swap out the Alternator and the problem is still the same, then you have a spare Alternator, and you will have to investigate the AC compressor some more. With the belt off you can put power to the compressor clutch to check it, you don't need the engine to be running. Here's the check list for the compressor clutch, the clutch itself is replaceable. But some special tools are needed, and it needs shims to make sure the pressure plate distance to the rotator is correct. It's not the easiest job at all. But you would hear a bearing noise from the clutch when the compressor was off. And it's the opposite of that. But let me know what you find when you take the belt off.

So far, I got a voltage drop of 1.45 volts with engine Off 0.140 with engine on can't check amps I need to get a amp clamp. One thing for sure, with no load it charges between 13-14 as soon as I turn on the headlights it stops charging and starts dropping fast. By the way the 140-amp fusible link shows continuity and no issues.

Okay, so it's not isolated to just the A/C compressor. 140mv is not bad. Were you able to do the A/C voltage test? And how low does it drop to with the headlamps on? This isn't with the new Alternator on, correct? This is the original one.

Haven't done the A/C test yet voltage drops to around 12 ish with lights on, same with the blower on almost full with the AC on and the cooling fans on the condenser, it drops below 12 to around 11 when I turn the load off it jumps back up to 12.5 but if I rev it up it goes up but it never goes back to between 13-14 this is with the better battery, yes it's the original alternator, I wonder if it could.be the ECM? No error codes no battery light staying on. I have the replacement alternator but I just want to be sure the cause is the alternator before replacing it and finding the problem still persists. Next step I guess is to take the belt off and check the pulleys. Thanks

Yeah, check the pulleys when you change the Alternator, if the last battery was no good it could have caused the Alternator to over work, if there were shorted cells in the battery, which can cause charging system issues. With 6 cells in the battery, if 2 were shorted together, then you really only have 4 cells. At 2volts per cell, you can see how a battery can cause problems. When I find a bad Alternator, and they have been like that for a while, I usually recommend replacing the battery too.
Now too much AC voltage ripple can damage the ECM because it's not designed to run on AC voltage. Thats the reason for testing for that as well.
But your issue sounds like just a bad Alternator that can't keep up, the Headlamps, the Blower motor, the A/C compressor, those are all large current loads.

Okay, will do. I will let you know the results.

Hello, I haven't gotten around to changing the alternator yet, I took the belt off looks like it did when I put it on, as for the pulleys, the alternator spins freely, the compressor spins freely the clutch does not it moves by hand not frozen, so I guess that's normal and the balancer pulley as expected doesn't move by hand, as I know it takes a lot of force to move that one. So I'm thinking I will give the old alternator one last shot, put the belt back on, try to find that sweet spot tighten it and see if it works if not, I will replace it, will let you know the results.

Only tighten the belt until you can twist it only 90 degree turn at its longest point, and not tighter.

I thought it was 45 degrees, which might be where I'm going wrong, obviously 45 degrees is tighter. I think I'm getting somewhere with the old alternator, I was able get over 13 steady with lights on but as soon as I turned on the blower on low with lights on it drops below 12 and when I give it gas still squeals, so it might still be to tight now I know it's 90 degrees and I'll try that see if it changes.

So, I'm going on the longest part being away from. The pulley, I think I have the sweet spot , so good news and, good is it's charging up past 13 with lights and brights on, bad as soon as I turn on the blower without A/C on the power dips down below 12 and still squeals when I give it a gas, so at least I can drive it at night, but as far as A/C forget about it. I think I need to get it looked at locally, do you still think it might be the alternator or compressor, could it be the blower? Thanks.

Forgot to add, keeps dropping when the cooling fans come on too.

It sounds like the Alternator is not able to handle the load, as for finding the squeal, you can try using a screwdriver, it's an old school trick, putting your ear up to the end of the screwdriver and touching the screwdriver to the alternator case, basically using the screwdriver as a stethoscope. If it's the bearing in the alternator making the noise, you'll hear it clearly. It sounds like the belt was too tight. The Blower motor is a high amperage component, I think the alternator is just not keeping up with all the load on it. The Alternator should be able to increase its output to cover all those loads. You can pull out the Blower motor and rotate it by hand to see if it spins smoothly, it's under the passenger side dash.

You were right it was the alternator, i finally gave in and replaced it today, but it was also the serpentine belt I put the old one back on and the bad alternator worked better but still had the A/C issue anyhow all good now. Thanks for the assist.