Glass like many materials expands and contracts with heat and cold. When you have a chip in your windshield the heat can cause the crack to open slightly wider, allowing for an easier repair. But, greatly increasing the risk of the repair splitting or breaking during the repair process. Pressure is applied during the repair which in turn, can also open the crack wider. A good rule of thumb to follow on hot days is to schedule your repair in the mornings when the weather is cooler. Thus reducing the risk of the repair splitting or breaking.
Blue Ribbon Auto Glass, LLC.