2001 85kmillege timing belt issue

Really could use some more information. You had a new timing belt put on? The timing is irratic? Explain more.

You havent even given the make model and engine type. If you want a good response, give all of the information along with what work was done, and what the problem was before the work and what the problem is now.

Are you talking about the auto-tensioner for the timing belt? What kind of problem are you having since he replaced the timing belt? Did it jump timing?
Heres the deal. If you replace the timing belt, any good mechanic should test the tensioner before reinstalling the belt. If it tested good when it was installed, then it is probably not bad. If the timing is off, I would suspect it was something that the mechanic did. Maybe it is the wrong belt? Maybe he didnt get the timing marks lined up when he put it back together. Either way, I would be screaming that he make it right. If the tensioner is bad, I would ask him why he didnt check it before when he had it off. A new tensioner should cost around $95. Have him show you the bad tensioner and how he has tested it to see if it is wrong.
I am not saying that what the mechanic did was wrong, I would just find out the facts, and have them explained to you in a way you can understand it. But do ask why this wasnt checked before, and why it wasnt bad before.
Now, if you are talking about the hissing noise, that is a totally seperate problem. But to my knowledge there is no tensioner on the A/C belt.