The idle or pulley will have movement in it, when the engine is shut off. It can also have a visible wobble while the engine is running.
It is a idler pulley.
yes it is!
There is a small bearing in there and sometimes they just fail. The bearing can't really be changed so you'll have to buy a new or used idler pulley.
From a standard socket wrench, the square part that fits inside the socket also fits in the center of the idler pulley (rather than buying a special tool that does the same). Fit the socket wrench (without the socket) in the idler pulley and turn to move the idler pulley and loosen the belt. Remove he old belt. Move the idler pulley again and put the new belt on. The diagram for the belt is on a sticker under the hood on the body above the grille.
Behind the water pump pulley. The pump is smaller than the pulley so the pulley hides it.
Need to know if you have a Detroit, Cat, or Cummins engine in order to answer this. As for the idler pulley itself, it's pretty simple to locate - it's the pulley which only spins, and doesn't actuate a pump, alternator, compressor, etc. Removing it is as simple as loosening the belt, unbolting it, and installing it in the opposite order.
Take off belt, remove bolt in center of pulley, replace with new pulley (comes with bearing). Reverse to install Take off belt, remove bolt in center of pulley, replace with new pulley (comes with bearing).
you dont adjust a tension pulley you adjust the position of the compressor to tighten the belt
The accessory belt assembly has a picture under the hood somewhere. If not, take a digital picture or two and print them out. The is an idler pulley, that is spring loaded. Generally, I've taken a small piece of rag or cardboard and put it into the jaw of the visegrips (so I don't gouge metal) and if you position it right, you can lock the grips onto the idler pulley. Pull in the opposite way of the tension on the belt. You should not have to pull too hard...slide the belt off the pulley. Then pull out the belt from around the rest of the pulleys. Release your hold on the idler. String back up the new belt, grab the vise grips, pull down on the idler, and you're home free.
When It no longer hold proper tension if the belt is squeaking then it is probably time to change it
The front bottom PULLEY on the engine is bolted to the blancer.
Before removing the belt either draw the belt's path or note the sticker showing the belt's path. Put the correct size socket on the center bolt of the idler tension pulley - pull the tensioner pulley up to loosen the belt - slip the belt off. Install in reverse order. The spring in the tensioner pulley is pretty stout, you might need someone to help you slip the belt back on.