When my car sits for awhile in warm weather, and then I start it up, I get this horrible loud belt squeal. I'm fairly certain it's in the A/C belt, but I could be wrong. Either way, it goes away as the engine itself warms up, but until it does it begins to squeal at progressively higher and higher rpms (it'll stop squealing at idle, but start again when I rev to 3000... then go quiet again until 4000... and so on until the car's been running for a while and they stop entirely). My hypothesis is that the warm weather is making the belts soft and looser, and I need to tighten them. But it doesn't make sense that they stop when the engine warms up then. I've also heard belts will squeal because they're overly tight. So what do I do? Tighten, loosen, or something else I haven't thought of?

 

Actually the belts are cold ( comparatively speaking) when you start it up. Then the slipping that occurs warms them and softens them. And they stick better. Kind of like a race car tire.
You might try tightening them a little bit.

 

rootski, i had almost exact same symptoms... tighten A/C belt just a bit, worked for me

 

Turn the A/C off before starting the engine.

 

And then turn it on................if it squeals, then you know it's the A/C belt. Tighten it just a little and see if goes away.