OT: What causes a drive belt to squeal?

[Jehu]

I have a '99 Chevy van. It has sometimes refused to start. It did this tonight. When i turned the key in the ignition i found i had left the blower on and the car didn't start. The Voltage was way down. I let it sit for a few hours,made sure the blower was off and it started but there was a shrieking squeal from under the hood. I guessed it was a belt because it eventually would stop when i turned off the blower . Seemed weather the heat or a/c was on at the blower selector it would squeal but when i turned the blower off it stopped. It had been doing this for a while and it has sat undriven for a bout 4 months. Will replacing the Serpentine belt fix this? I;m not sure if its loose,shrunk or slipped a pulley but it seems when i try and start it and the blower is on,weather with a/c or heat,there isn't enough juice to start which sounds like the alternator isn't able to turn fast enough to create the current for ignition. Or is is the a/c compressor clutch that's not allowing free spinning of its pulley?Any ideas?

[Fetch]

Squealing would be from loose or dry/old belt maybe?
Not sure how it's related to the blower being on and not the a/c?

I don't know enough to make a good guess on this one....

The spinning of the alternator doesn't help starting, the onus is on the battery for that.

[Chris'91'525i]

Squealing would be from loose or dry/old belt maybe?
Not sure how it's related to the blower being on and not the a/c?
I don't know enough to make a good guess on this one....
The spinning of the alternator doesn't help starting, the onus is on the battery for that.

Possible bad belt tensioner too. It takes alot for a serpentine belt to slip.
Take the belt off to inspect for frays, cracks or being gazed. And then check that all the pulleys that spin, spin freely.
If it still makes noise after a new belt, it's probably a tensioner. I believe these need to be replaced as preventive maintanance anyway, so it might not be a bad idea to replace it anyway.

[Jehu]

Possible bad belt tensioner too. It takes alot for a serpentine belt to slip.
Take the belt off to inspect for frays, cracks or being gazed. And then check that all the pulleys that spin, spin freely.
If it still makes noise it's probably a tensioner. I believe these need to be replaced as preventive maintanance anyway, so it might not be a bad idea to replace it anyway.
groovey, thanks for the idea!

[BillionPa]

could also be the alternator or a pump starting to sieze up and putting stress on the engine during startup.

[Jehu]

could also be the alternator or a pump starting to seize up and putting stress on the engine during startup.
Yah it did it again tonight when i tried to start it . Just didn't kick over.I had the alternator replaced early this year but its strange i can't recall if i had the water pump done. I've done so much to this thing i might be blocking out the memory at the moment but i guess there's no easy way to tell what it is .I want to either sell it or give it to my son but i can;t do either when it's not reliable.I drove it a few hundred miles on Wednesday but later in the evening it wouldn't start when i needed it at about 7:30 pm and i did when i tried it a couple of hours later... oh well .. thanks.