I go with dadu here - the reception would be climate-controlled. Why waste fuel idling a car just to keep you cool, when you have better env-friendly options ? Or as others said, find some tree or shade (not shady place
) nearby.
As a policy, I never ever idle the car just for the a/c. But recently have had to break it for my li'l kid due to the weather in Kerala being pretty hot and with no sign of any rains.