Does not turn serpentine belt sometimes but the small fan belt turns.

Which belt was changed .......
Fan/serpentine belt or timing belt.

I would check your cooling fans. When you turn on the AC, it probably starts a second fan. Maybe the other one is not working?

that is your problem (fan switch)

Check with Autozone and discuss your problem. They know what they are talking about and have always come up with the right parts or belts for me. I used to be a mechanic in my youth and I never go anywhere else.........

Sounds like the fan belt or serpentine belt is slipping ,get a spray bottle put a little dish soap in it
and mix with water, spray on fan belt, now start the car and turn on your ac, if the noise goes away
you need to replace your fan belt or serpentine belt, if the noise persists, you may have a bad
tensioner pulley. good luck!

the serpentine belt is the only belt in this p/u truck,its breaks off in strips the length of the belt

You will need to keep the pulley from turning, somehow. Or use the correct tool. Sometimes you can give the wrench a good whack and it will knock it loose.

The symptoms you have described sounds most like you had a serpentine belt break or fall off the pulley system (rare but possible).That is a fairly simple job to replace the serpentine belt,whether you replace it yourself or have a professional do the job it isn't a costly repair, providing that is the only problem.There is a serpentine belt routing label under the hood, usually on the plastic piece that goes across the front of the engine compartment near the hood latch release.There is a spring loaded belt tensioner that holds tension on the serpentine belt(labeled on the routing label) rotate the tensioner against the spring pressure, rout the belt according to the routing label, then slowly release tensioner against the new belt and that should complete the installation.Hopefully that is the solution. Good luck !

Remove the belt and check all pulleys for smooth operation. any binding at all is amplified when belt tension is applied. also check the belt itself...If it's glazed or dried out, it can be noisy.

is it a squeal noise or what? explain more in detail. and yes the belt is directional in that it's path is designed to run in one direction only, no matter which side you put on the belt itself, the belt can be installed in one way or flip it over to the opposite side...doesn't matter, only matters if you installed it correctly on the routing of the belt. And the grooved edge is to be facing down inside the main pulley's that have grooves. If you have the smooth side down into the pulley grooves, remove teh belt and turn it inside out so that the smooth side does not ride inside the grooves of the pulleys.Sometimes, the tensioner pulley will squeal or the idler pulley will squeal when they are going out. If you are actually hearing the fan come on and off, that's normal, the fan is set up to turn on and off according to engine temperature and some cars they continue to run for a bit after ignition is turned off as well to cool the engine down. check to see if the belt is set all the way on all the pulley's it rides on and not partly off on the edge, realign as needed.