tensioner loose? Normal?

Looking to buy a 2005 1500 Silverado w/ 5.3 V8. There is a belt all by itself that runs what looks like the A/C unit. The tensioner on that belt moves up and down in a jittering motion. Is this normal or should this be replaced? Rest of the truck is cherry.

That jittering is normal- although there have been issue with compressors that seize and destroy the belt- as long as a/c works and is quiet- I would not let it affect the deal...

See if you can reach down there and pull the tensioner by hand to take the tension off, if you can make them replace it, its bad. If not its fine. I had the same question about my truck when i bought it in October and had the shop look at it before i bought it cause it was also making a squeal when the compressor would kick in, and they said it was a insignificant noise, well it was loud as heck and i just wanted to get out of there so i went to the parts store and picked up a new one for like $15 went home and took off the belt and i could move the tensioner back and forth all day long with no problem, all the tension was gone, so i put a new one on and a new belt, and bam! no more squeal, dealerships are a bunch of crap, it probably would have taken them less time to just change the tensioner than to write on the work order that is was an insignificant noise. So check that out before you buy, and if it does take a dump, its a cheap easy fix.

Looking to buy a 2005 1500 Silverado w/ 5.3 V8. There is a belt all by itself that runs what looks like the A/C unit. The tensioner on that belt moves up and down in a jittering motion. Is this normal or should this be replaced? Rest of the truck is cherry.

this is not normal....... this idler should not be moving around slight movement when you rev engine is normal.... belt will have to be removed to diagnose whats up could be idler pulley....or compressor pulley bearing and if it is this bearing it will be expensive ..