I have heard two opposing viewpoints on this and don’t know which to believe.
Theory A: When starting a hot car on a hot day, open the windows and run the fan until you’ve blown out the hotter air inside the car. Do not start the AC right away, as it wastes fuel and is hard on the engine.
Theory B: On a hot day, the fan blows hot air for at least the first few minutes. It’ll take much longer to cool the car interior this way and won’t save much if any fuel. Open the windows, crank up the AC, and within a minute or two, shut the windows and enjoy the cool air.
The theory B person suggested opening all four windows first, followed by shutting the front windows and then the back windows in fairly quick succession, so the AC “chases” out the hot air.
Theory A sounds more plausible to me but also more uncomfortable. Is it really more fuel-efficient?
Thanks for any answers. I’m a shame-faced physics idiot, so I especially appreciate any information on a Dr. Seuss level.
Get in the car and turn the AC on full blast. This will get you cooler faster rather than wasting YOUR energy rolling windows and wasting time. Any potential fuel cost will be minimal. The engine is designed to handle the load because it compensates when the AC is on. Sure AC takes energy and burns fuel. You want AC, turn it on I say.
PS. A properly maintained engine should last the life of the vehicle these days unless it is a commercial vehicle like a cab.
Crank up the fan. Maybe or maybe not crank up the AC itself. Drive around for a few minutes with the windows down, depending on how hot it is or isn’t. Blow out all that super heated air first.
Or in other words blow out all the 140 degree air and replace it with 100 degree air. The AC will cool that down much faster. 140-80= 60 degrees to cool. 100-80=20 degrees to cool down.
Its not so much about economy or wear an tear. Its more about whether you want the interior of the car to be tolerably cool in 5 minutes or 10 minutes.
Crank A/C to Max, fan to High, roll all windows down to flush out super-heated air for about 20-30 seconds of driving, and then it’s merely a battle between the mega-hot surfaces that are radiating heat and your A/C. It’s gonna take a few mins for the A/C to get to it coolest. While it is getting up to the task, you’re flushing out hot air.
If you concern yourself with staging the windows (fronts up, backs down), get help immediately.
The instructions above (window staging aside) are the instructions in many owner manuals nowadays.
I hope I’m not the only one without automatic windows, wondering how I’m going to manage all this window rolling… Do I need to be rolling windows up and down while the car is actually moving, or is it enough that the engine is running?
One can over think some functions and I think this is a good example. There’s nothing particularly illogical with the above, but I doubt the end result (a cool interior) is effected to any great degree. On a somewhat related subject, and perhaps another example of over thinking, I don’t start my engine with the A/C on as it is as the compressor does as resistance to the starter motor. However if the added drain was anything significant, the manufacturers would note it as such. Sometimes us car guys are prone to over analysis.
I’m fairly sure most AC systems these days are designed in such a way that they won’t energize the AC compressor clutch until the engine is actually up and running, so turning the AC off before starting is no longer necessary.
All cooling effectiveness aside, the differential fuel use by running the air conditioner compressor a minute longer or so is hardly measurable. And yes, pretty much any modern car made in the last 20 years probably de-energizes the air conditioner compressor while the starter runs.
Park so the front of your car does not face the sun. This will keep the steering wheel and seats from becoming so hot to hot to touch. (learned this from a friend in Phoenix)
Leave the windows cracked an inch or so will keep the interior way cooler on a hot day.
Start the car turn on the AC and enjoy is my advice.
BTW the electronic climate control in my car won’t go to full atomic power unless the windows are up. Guess the designers figured out the AC was not strong enough to cool all of LA.
Getting the A/C on sooner will cool the car off sooner. It is not “hard on the engine,” that’s nonsense. Your car was designed to use it, and the first 2 minutes are no harder on the engine than the rest of your 30-minute commute.
Getting hot air out faster will cool the car off (a little bit) sooner. So open windows, but this process is less than 1 minute. A lot of the hot air escapes just from opening the door.
Air does not have a very high heat capacity compared to the surfaces, seats, and metal inside your car. Even after the *air *inside the car is cool, the hot surfaces will continue to heat the air until they cool off, which takes a while. The air itself is the least of your worries.
My approach is to push the button on my remote that opens all of the windows, including the moonroof, as I walk to the car. I start the car, put the A/C on automatic (why would I buy a car if I can’t trust the features to work) and start driving. In about 15-30 seconds I figure I’ve gotten all the benefit of open windows and air flow and I close the windows. I want to car comfortable and am willing to pay the few cents of extra fuel.
It looks like Theory B is the winner. Interestingly enough, Theory A was expounded by my ex, who often spoke authoritatively enough that I believed him–even when, it turns out, he didn’t know what he was talking about. Theory B was my mom’s take; she was 89 when she died last winter. Yay, Mom!
I have a light colored truck, and live in Lake Havasu City AZ. Temps outside right now are averaging in the 105-110+ range. I use a reflector in my windshield to protect my dash, but doesn’t do anything for the temperature.
I get in, roll down the front windows, blast the A/C on high fan at max temp and will keep it this way for the 1-2 minutes it takes me to get out onto the highway from work. I normally cut it down to 50% fan and roll the windows up - lasts me the 10 minute drive home just fine.
You put the reflector in the windows that have sun coming in, regardless of how you’re parked. It’s easiest to put mine in the front, so if I’m going to use it, I park front-to-the-sun.
The hot air will be dispelled more quickly through an open window, but I doubt it’s worth the trouble to open more than one.
Cool air will arrive more quickly with turning the A/C on right away. There’s really no reason not to.
The little-known technique that is worth doing is to start with taking in outside air rather than inside air, assuming the car has been parked in the sun and the air inside it is hotter than the air outside. In most American cars that means regular A/C rather than MAX A/C. In most Asian cars it means switching off the RECIRC (recirculate) button, or moving the lever from the U-shaped arrow (recirculated air) to the straight arrow (fresh air). No sense trying to cool down 130º air when 95º air is available. Once you get some cooling inside (a minute or two), switch over to MAX A/C or recirculation. Then the system will take in the already partly cooled air from inside the car and cool it even more.
Set the A/C as follows: outside air, directed towards floor and face, fan on full, turned all the way to the blue side of the dial.
Rear windows cracked just a bit.
Drive. This element is crucial, as to my knowledge most modern cars won’t kick in the A/C compressor if you’re just idling.
Bringing in outside air is almost always going to cool you down faster than using inside air at first, because the air inside is usually hotter at first. ETA: What GaryT said while I was typing.
Directing the air to both feet and face helps to push the hot air up and out the cracked windows in the back while still giving you some feedback on when it has started cooling off.
When you start to feel cool air on your face, the inside is now probably cooler than the outside, so turn to recirculate air, close the windows in the back, and feel free to adjust the output wherever you like it.
Right. No accessory is turned on while the starter runs. So you don’t have to turn off the radio or fan before turning off the engine. No excess drain on the battery when you start up because no accessory runs right away.
