Dear Car Talk:
Is it harmful to start the car if the air conditioner, radio, etc., have been left in the "on" position?
Yes, that's why at the shop, we recommend to all of our customers that they leave their cars idling from May through September.
Actually, no. It's not harmful at all, Stanley. For two reasons.
First, cars automatically shut off auxiliary power while the car is cranking. So when you turn the key to crank the engine and start the car, the AC, the radio and virtually every other electrical device is shut off anyway. That allows the maximum amount of current to be directed from the battery to the starter motor, where it's needed.
Once the car starts, power is restored to the accessories, and they pick up wherever they left off.
The second reason it's not a problem is because it doesn't matter when you turn them on -- you're still turning them on. They're designed to be turned on suddenly, whether it's when you start the car, or when you flip their on-off switch.
So don't worry. None of these devices need to be gently shaken awake in the morning, like I do.