Mine have never stayed in the car alone.Someone stays in the car with them,with the a/c on.I refuse to leave them alone.I'll only leave them if were filling up the gas tank or something like that.
Its illegal here to leave your dog in the car in the summer.It get's so hot here,and many animals have died from people leaving their dogs in the car. You have your dog taken away if its left in the car,and if someone complains about it.