Is it advisable to roll down windows before switching on AC

The air circulating inside the car contains higher levels of benzene, due to the heat emanating from the hot plastic.

BHPian Anees_Offl recently shared this with other enthusiasts.

I always had this doubt in mind. Different people had given me different answers. So, thought of posting this in this forum.

We all know the temperature inside a car will be much higher than the temperature prevailing outside. Let's take the case of Indian weather conditions for example, where

  • If the car is parked under a shade/garage, the temperature hovers around 30 - 33 degree Celsius.
  • If the car is parked outside (directly under sun), then the temperature can go up to 38 - 44 degrees (or more) depending on the prevailing weather conditions.

There are people who religiously ensure that the windows are open before switching on the AC.

This article also advices us the same.

The air circulating inside the car contains higher levels of benzene, due to the heat emanating from the hot plastic.

While that being the case, I have seen a few people who are allergic to rolling down their car windows (even for a minute) due to obvious reasons.

So, to sum it up, we have these questions.

  1. Isn't it a good idea (or) isn't it advisable to open windows to expel trapped gas before turning on the AC, at least for 5 minutes?
  2. If it's for our own and our family's well-being, why are people avoiding to do so?

Here's what BHPian akshay4587 had to say on the matter:

These days, my Polo is parked out in the open during the day, and I cannot thank enough VW, for being able to roll down windows from remote before I walk into the oven.

Once Inside, I turn on the AC and roll up front windows and let the rear ones open for some time to let the hot air escape.

Here's what BHPian IamNikhil had to say on the matter:

What I have religiously followed always is rolling down all windows for the first few minutes after starting the car and putting the fan on. I switch the AC on after approximately driving for 2-3 minutes. Have utilised this technique in all weather conditions. Also, during the summer, I open the sunroof for a couple of minutes, to allow the internal heat to dissipate faster.

Here's what BHPian Dr.AD had to say on the matter:

a) Yes, it is a good idea. It is always a good idea to expel out the hot air. However, it need not be strictly done before starting the AC. And also, it need not be for 5 minutes. Once your car is moving, even 30 seconds is enough to expel out all the trapped air and get in fresh air. This could easily be done even after you switch ON the AC. The main logic is not to burden the AC with cooling down the trapped hot air. That is the idea. There is no harm if you switch ON the AC first, and then a few seconds later roll down the windows.

b) There could be reasons to not roll down the windows, on some rare occasions. For example, if I parked in an area with foul smell or unclean air, or if it is raining heavily, I do not roll down the windows until I get out of that area. It is not like not rolling down the windows is going to cause any immediate or any noticeable harm to your AC. All it will do is make your AC work extra hard for a few minutes. Also, maybe a couple of minutes of breathing in that trapped air is not going to cause any danger to you.

Of course, case b) is a rare occasion, and almost always, I follow the practice mentioned in case a).

Yes, fresh air mode will do that job of swapping the air, but way too slowly. This is not the intended use of fresh air mode. The intended use of fresh air model is to get in fresh air as and when needed (or sometimes in continuous mode), at a small rate, once the internal temperature is already somewhat stabilized to desired levels.

However, when you get in a parked car, there is a large volume of air which is hot and stale. It is best to expel this out as quickly as possible, and not burden the AC system with the job of cooling down this large static mass of hot air. Rolling down the windows even for 30 seconds will do this job and do this quite well.

On the other hand, if you solely depend on the fresh air mode to do this job, it might take 15 minutes (or even more) of overloaded AC operation under fresh air mode to completely swap the air mass trapped inside with fresh air while simultaneously cooling this hot air. The AC will be doing a lot of unnecessary work of cooling down the air which is much hotter than the ambient temperature.

Here's what BHPian anjan_c2007 had to say on the matter:

Always desirable especially during hot weather and post "non-use" spells when it is very necessary.

When parked in heat during sunny days (also summers) the interior temperature touches 50 degrees Celsius or even more at times. The hot air needs to be cleared and the windows are needed to be rolled down. Only after we can see a reduction in interior temperature should we roll up the windows and switch on the AC.

Similarly during many days of "non-use" the stale air inside the cabin needs to be freshened up.

However, on dusty of smoke/smog filled stretches, our own judgment needs to be used while rolling down the windows. It's better to allow such hostile stretches to pass over.

But apart from the other factors, it is also very important to get rid of the toxic benzene formed inside the cabin due to heating up of the plastics and the upholstery. This finding was reported by researchers I believe about a decade ago.

Check out BHPian comments for more insights and information.

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