Belt squeals

[RedArrow]

Started doing it today… Issue #1: My alternator belt squeals as the engine revolution goes up. It ONLY happens if the heat is switched on in the 2nd position or up (3rd or 4th). Symptom #2: When I switch the heat on, the voltage gauge shows the voltage dropping quickly down, immediately, from 14-15V to 10V. It gets even lower if the headlights are on, even more if the high beam is on (with the heat). Rising rpm does not stop the squeal nor rises the voltage levels back to normal. If heat is not on, there is no squeal.
In the past I rarely saw my voltage dropping down lower than 12V, and never more than 1-2 Volts at once... and those times it always happened gradually/slowly (for example when I switched the seat heaters on with full blast of heat, radio, headlights+front fog lights+rear fog lights on +radio +etc ). That`s normal, I think, that in that case the voltage drops from 15 to 12-13-14, whatever, and stays there, being lower than the average I see when driving with nothing on (daytime).
Now, as I put the heat on, the voltage immediately jumps down from 15V to 10-11Volts and the belt starts to squeal too as the rpm increases. It does not stop. If the heat is not on, the voltage stays around 14-15V and there is no belt noise at all. (PS.: The digital Voltmeter shows 14.06V in battery after many days of no-use.)
It’s a nasty cold rain here and completely dark now but I`d like to figure this out tomorrow. Any ideas so far?

[ngoma]

Alternator belt needs to be very tight on these. If yours slips when electrical load is applied, see if you can solve the problem by tightening the belt. Helps to use a crowbar for leverage but be careful not to place the crowbar against any fragile parts.

Also, check the condition of the belt itself.

If the belt is slipping, the gauge will read lower because the alternator is not able to meet the electrical demand.

If tightening the belt does not help (should at least stop the squealing), then start looking at possible failing heater fan or resistor pack, and wiring issues.

[RedArrow]

Thanks Ngoma for your opinion! Right after I posted my question here around midnight, I could not got to sleep (again) so I adjusted the belt in the middle of the night. (I was about to post another question again with the results of the fix.) I then saw that you answered me... Just as you suggested, the belt was not tight at all. It has a Volvo belt on the alternator and it looks, feels healthy. Squealing stopped right after tightening the belt. I did what you suggested but I was not sure how tight it is allowed to be. I attacked the 13mm nut and adjusted it... now it`s tighter but I can still push the belt `down` half an inch. Shall I go ahead and do it again?
I still have the voltage gauge drop big time if stuff inside the car is turned on, especially when I turn the heat on full blast (with lights etc)....
The high-pitched squealing belt noise stopped though. I might want to go back and tighten the belt more. How would you make sure that tension is right?
I`m curious if it is a good idea to use an additional bolt/nut in that gap to avoid any future incidents like this one?

[ngoma]

If the belt stopped slipping (squealing) then you got it tight enough. How much did that improve the low voltage situation?

PS: Try a different DVOM. A fully charged 12V auto battery should read 12.6-12.8 VDC. Your measurement of 14.06 for a resting battery is way too high.

Your FLAPS should offer free testing of the charging system and battery, have you tried that?

[RedArrow]

I tightened the belt. I could make it even tighter if I knew how much the desired/suggested max tension is. At this stage I can still bend the belt slightly or push it down half an inch. It could be tighter but I was not sure about specifications. The slipping ended so there`s no belt noise any more but voltage still drops down immediately to 10-11 Volts right after I switch things on such as heating, fogs, headlights, etc, especially if I combine these... I will check on the battery but I guess it is not malfunctioning yet. I do remember though that my voltage gauge showed around 15-16V all times throughout thousands of miles. Also, my newish loose alternator belt issue might be somehow related to my power steering pump minor leaking and/or that belt`s abnormal running angle (misaligned a bit). I have a post about that too. I can`t think too much about this car or anything right now these days but will be on it very soon, hopefully.

[v8volvo]

Did the tachometer reading also drop when the squealing occurs? Usually when the alternator belt is slipping you can see it on the tach, since the tach reads RPM off the alternator.

Now that the squealing is gone, but you are still noticing the voltmeter reading low when the electrical load is high, does the tach still stay steady? If you are seeing big variations in your voltmeter reading but the tach is reading normally, then the belt is probably tight enough now and the voltmeter is probably just a little oversensitive given the range of its fluctuation. Well, either that or the voltage regulator is acting up and/or brushes are worn.... You might want to get access to a known accurate voltmeter and check charging voltage at the battery with engine idling and electrical accessories, lights etc turned on to ensure that the alternator output is sufficient and correct, but it sounds like you have probably cured it.