Once a serpentine belt breaks on a 2003 S-500, is it absolutely necessary to replace the pullies, air compressor, etc. or just the belt? What is a reason price for just replacing all involved parts?

What kind of damage happened to required all of that to be replaced?

Not necessary unless they were damaged, but then again idler pulleys and belt-tensioner pulleys are cheap and easy to replace, so why not when you have it all apart? Question is what caused the belt to break? How many miles on it?

About 90K miles. Last week, air suddenly stopped cooling. Then after a few more miles, we lost power steering and the battery light came on. We immediately pulled over and had the car towed to a shop we've dealt with before. The mechanic is saying that in order to warranty the belt, he needs to replace all the parts. He did suspect that one of the pullies malfunctioned which caused the belt to break. However, how would you know just by looking at it that air compressor, etc. need to be replaced? I would hate to spend the value of the car trying to repair it. He is working up an itemized estimate. My husband is trying to work with the mechanic but I'm just trying to get a second opinion. Basically I want to repair ONLY what is necessary. Contemplating selling the car.

From your description, it sounds like the AC compressor failed first, if the clutch froze it eventually caused the belt to fail. They can test the AC compressor to see if it spins at least. When replacing a belt it is good practice to replace idler and tensioner too. The only other pulleys to check would be alternator and power steering, you shouldn't have to replace those unless they are also bad, but your mechanic should be able to tell. Let him replace the belt, idler, tensioner, and if needed AC compressor. It'll cost more, it is a Mercedes after all.

I had a similar problem, it should be around $700-1000 max.

I have a Mercedes ML430 year 2000, the belt keeps on breaking I read some of the comments here and I taught it might be the compressor tensioner or power steering, I recently replaced a tensioner so it's not that, I don't think it's the compressor because the wheel does spin, but my power steering is kind of tough when I'm making turns or parking so I am guessing I have to replace the power steering