Japanese Maples can suffer during hot summers if not kept watered. Leaves turning brown and crispy in the summer are a sure sign of dryness and drought. Water your maple more frequently during the hot summer months and if you can, choose a location in the part shade / part sun as opposed to full sun. Water deeply with a garden hose at least 1-2 times per week.
In most cases, the Japanese Maple will re-leaf either after being watered or next spring. Don't panic. Give the tree time to recover before deciding to remove it from the garden.