Need to replace serpintine belt but the tensioner will not move. What should I do?

You can look at tensioner and see which way it will turn,with racket,you may have to turn from below.It is a tight fit but bolt doesn't need to be loose.

You don't take anything off

You just put a long 1/2" ratchet in the hole on
the tensioner & Pull against the spring tension until
you have the belt over the final pulley

sounds like the serpintine belt is worn out and slipping. if the belt isn't turning, the a/c, powersteering and the alternator will not function. if this is the case replace the belt. another thing to check is belt tension. with the engine off, try and move the belt up and down. it should only move about a half inch either way. if it moves more than that and your vehicle has an automatic tensioner the tensioner has failed and needs to be replaced. if your vehicle has a manual tensioner try tightening up the tensioner.

Use a 3/8" breaker bar to move the belt tensioner. While holding pressure on the tensioner, remove the serpentine belt from any of the pulleys. Gently release pressure from the tensioner. Remove the old belt and replace with the new one. Reapply pressure to the tensioner and pop the belt over the last pulley.

This answer is for a 2003 Toyota Camry listed by the Asker under the 2001 Toyota Avalon Category

Click on the following direct Link. It has the Serpentine Belt Diagram.

Standard Rules to Removal the Serpentine Belt with a Tensioner:
1. Find the Tensioner(s). (See Diagrams on Link)
2. Using a Serpentine Belt Tensioner Tool, Or Wrench OR Ratchet, Rotate/Move the Tensioner USING THE AVAILABLE NUT (on the Pulley or Arm Base) OR the OPENING (3/8ths or 1/2 inch square opening) rotating the Tensioner Pulley/Arm - moving it away from contact with the belt and towards the area where the belt is not in contact with the Tensioner Pulley. The Tensioner is spring loaded, and is hard to rotate/move.
3. Remove the loosened belt off one of the other more easily accessed Pulleys.
4. DO NOT quickly release the Tensioner, but gently allow the Tensioner to rest in its closed position.

Standard Rules for Installing the Serpentine Belt with Tensioners:
a. Pick a Pulley that is most easily accessed. This will usually be on top. This will be the last Pulley that the belt will go on.
b. Using the Diagram: Install the new Serpentine Belt on the remainder of the Pulleys....over, under, left right.
c. Using a Serpentine Belt Tensioner Tool or Wrench or Ratchet Tool: Rotate/Move the Tensioner Pulley/Arm "away" from Belt contact area on the Tensioner. This spring is pretty hard and with a new belt, it will be even harder to install. Rotate/Move this to as-close to the maximum allowed inorder to have enough slack in the belt to get it up and over the last pulley.
d. Using your other hand - Pull the Belt up and over the Last remaining Pulley.
e. Before releasing the pressure on the Tensioner, visually inspect the remainder Pulleys and the Belts' Positioning on them

Let me know if this helped, or if you have additional information or questions. Feel Free to contact me at FixYa.Com!
http://www.2carpros.com/car_repair_information/year/2003/make/toyota/model/camry/2003_toyota_camry_drive_belt_routing_diagram.htm

On belt tensioner pulley fit a wrench on the bolt that holds pulley, turn clockwise to release tension, hold and remove belt.

no it needs a 3/8 drive

The serpentine belt tensioner / pulley is on the front of the engine, and part of the belt 'routing'.

Its job is to put tension on the belt as it drives the other devices like the power steering pump, water pump, air conditioning compressor.

It is an aluminum casting that mounts with a single bolt to the engine. The pulley is attached to the arm.

There are a few ways to move / pry the arm inwards, thus releasing the tension on the belt for removing/installing: grab on the pulley bolt (15mm?) with a wrench, or some later models have an opening for a 3/8th socket wrench to attach to directly without a socket.

If the belt keeps slipping off the you need to replace the tensioner(its the pulley you have to move to get the belt on and off,and that part should be inexpensive to replace from any parts store.

bring belt tensioner to where all the way moved
make sure you have belt set once you get the tensioner moves over the belt slides the rest way on and tensioner goes against belt
make sure belt is lined up properly