That smothering wall of oppressive heat waiting for you when you open your car door is undoubtedly the worst part of summer, to say nothing of the occasional burn from a searing-hot seatbelt. If you don't get your car cooled off ASA-freakin'-P, you'll be a miserable puddle of sweat before you get where you're going.
So what's the fastest way to get the heat out of your car? I decided to run some scientific (-ish) tests: park my car outside in the Texas sun for a few hours, several days in a row, measure how high the interior temperature climbs, and then experiment with various ways of cooling it off while timing how long it takes. The results were more dramatic than I expected, with a very clear winner that will certainly be of use to you this summer. You're welcome.
Method 1: Blasting the A/C and waiting
Temperature change in first 10 minutes: 1.8 degrees/minute
To get a control reading, I did the most obvious, basic thing imaginable. I started the car, hit the "MAX A/C" button, and let the system do its thing. I didn't even drive around, which was the best I could do to simulate horrific rush-hour traffic -- that's important, because your A/C relies on flowing air to help get rid of excess heat.
The car temperature when I got in was a balmy 128 degrees. After a nice blast of hot air to my face, courtesy of the register, cold air began to flow within a few seconds... but the rest of the car? Still baking. Ten minutes later, the air was down to 110 degrees. After 15 minutes, it was at 107. By the time 20 minutes had passed, it was at 103 and my neighbors probably thought I was insane. I cut the experiment there. It was right at 100 degrees outside, so 103 inside wasn't all that bad...
... Twenty minutes, however, is. You wouldn't exactly want to walk into a business meeting afterward.
Method 2: Driving with the windows down (and blasting A/C)
Temperature change in first 10 minutes: 2.5 degrees/minute
For day two, I did what I assume most people do when they're getting into a hot car: I rolled the windows down, hit "MAX/AC," and drove off. The cabin was cooler than the previous day, at only 126 degrees. I rolled the windows back up after two minutes, and by the seventh minute, the temperature was down to 110 inside the car. It was down to 101 by the time 10 minutes had passed, and after 15 minutes, it was down to 97 degrees. That's a full eight-degree advantage over the control.
Method 3: Driving with the windows up (and blasting A/C)
Temperature change in first 10 minutes: 3.1 degrees/minute
On day three I hit "MAX A/C" and drove off, but kept the windows up. The car's temperature went from 138 to 122 after five minutes, to 107 after 10, 94 after 15, and ultimately wound up at 88 degrees by the time 20 minutes had come and gone. I know what you're thinking. It's somehow faster than opening the windows?!? Well, that kind of makes a lot of sense. When you open your windows, you let plenty of heat out, sure, but you also let out plenty of that blessed, blessed cold air. It more than cancels out, and you don't effectively start the cooling process until later.
Method 4: Fanning the door
Temperature change in first 10 minutes: 3.6 degrees/minute
I pulled out some physics for this one: I rolled down the passenger-side window, then "fanned" the driver's-side door about half a dozen times. The idea is to create a low-pressure area that literally sucks the hot air out of the car. When done, I started the car, pressed the obligatory "MAX A/C" button, rolled up the passenger-side window, and drove off. The car sat for a little longer on this day, and the temperature spiked to 135 degrees, which would've been a good start if my goal was a nice long sweat in a sauna.
After five minutes, it was only down to 124... and then came a much bigger difference than I anticipated. Just one minute later, it was 116, followed by 107 after another 60 seconds. By the 10-minute marker, the temperature was already below 100, at which point I switched off dear old "MAX A/C." Five minutes later, the ambient temperature was down to 91 degrees. It didn't stop getting cooler and cooler, though, and by the time 20 minutes rolled around, it was a downright comfortable 86 degrees. Outside, it was the same 100-degree day as the previous two.
And the winner is...
As you can see on the chart, fanning your car by opening and closing your door a few times with the passenger-side window down is still a faster way to cool off the car for the first few minutes. It actually wins the degrees-per-minute battle by a score of 3.6 to 3.1, whereas the control is 1.8 over that time frame and driving the first two minutes with the windows down is 2.5 degrees per minute.
The biggest takeaway: keep driving
If you know anything about air-conditioning systems, you know that they require an immense amount of wind passing over the condenser (the radiator-like object that's usually next to the, um, radiator) in order to effectively transfer enough heat. This is why many cars have a dedicated auxiliary fan that can help out if you're not moving fast enough. However, the system isn't optimized to run while you're stopped for long periods of time, as evidenced by the graph -- not to mention it's by far the worst option for your car's long-term health. Whereas the control test is clearly the outlier of the group, the other three tests all generally coalesce around a point of diminishing returns.
In other words, go ahead and open the passenger window and fan the driver's-side door, but whatever you do, drive around if you want your car to cool off faster.