98 Dodge Caravan

I recently had the tensioner replaced on my dodge van. However, the old belt was not replaced at the same time. The tech said it looked fine to him but as soon as I drove off the lot and cranked up the a/c it broke. Now I have been desperately trying to schedule an appointment to get the belt replaced. Aren't the belts supposed to replaced rather than stressed and put back on? Keep in mind I live in Florida and at this time of the year it averages about 90 degrees outside.