If I understand properly, setting your vehicle in the AC setting will cycle air from the outside into your vehicle attempting to cool it before it is pulled in. Likewise, MAX AC only recycles the cabin air not pulling in any air from "under the hood."

With that being said, if it is HOT in your car from sitting in a parking lot all day (10+ hours) -- would it get your vehicle cooler if you turn on AC and allow your vehicle to "cool" the outside air being pulled in. OR use MAX AC where the HOT cabin air is just cycled throughout your cabin?

  • 1
    FYI - outside air is usually pulled from the exterior vents at the bottom of the windshield. – MooseLucifer Jul 20 '16 at 19:23
  • Also, if our car from sitting in a parking lot all day (10+ hours) then I would not start with AC. Instead drive the first kilometer with all windows open. That will quitely replace your sauna with normal hot air. Then turn on AC and close the windows. – Hennes Jul 21 '16 at 7:52
  • @Hennes - I have tried this approach, and (albeit I am now thinking I should get my cooling system checked) I must ride with the windows down for roughly 12 miles and even then the AC is not capable of blowing iceberg temp air out. – user2676140 Jul 21 '16 at 12:00
  • 12 miles seems quite a distance. I can understand no perfectly cold air within 100 meters, but 12 miles is really to long. – Hennes Jul 21 '16 at 13:50
  • @Hennes - that is what I was thinking as well. I am planning to take it in to have the AC checked out either this afternoon or 1st thing in the AM – user2676140 Jul 21 '16 at 13:53

Ok, let's break this down a bit. A/C systems have two basic modes:

  • Outside air
  • Recirculate

When you are in outside air mode, the vehicle will allow air from outside the cabin to enter.

Recirculate means that the vehicle will mostly use the air already inside of the cabin.

Note that both modes allow air to be from both sources. You will get outside air in recirculate, and you will recirculate in outside air. What you change is the amount.

The common approach to cooling a hot cabin is to turn on the A/C and let outside air in. This is done to replace the hot inside air with fresh outside air. Once the hot air has been replaced, the recirculate mode is turned on to increase the speed air is cooled inside the cabin. Its easier to cool air that has been recirculating inside the cabin than outside air.

Why does MAX A/C work for you?

In modern cars, the MAX A/C settings gets an initial burst of outside air in the first few seconds of operation and then starts to recirculate it. It is a hybrid setting that allows you to get cold air as soon as possible. If you car has an intelligent multi mode climate control system then you are going to have to ask the weather guy to help you figure it out. :)

  • Also, it can't be a bad idea to initially (and quickly) purge the stale air with outside air before going to MAX AC; the solvents used for upholstery and surface finishes, and glues, contain toxic stuff like formaldehyde. That stuff slowly volatilizes, especially when temp rises. – Jimmy Fix-it Jul 21 '16 at 5:00

I would have thought it would be more efficient at first to pull air in from outside as it will initially be cooler than the cabin air. After a few minutes I would change it to MAX AC to recycle the cooler air from inside the cabin, making it even cooler.

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    I will give that a go in a few on the commute home and see if I can tell a diff. – user2676140 Jul 20 '16 at 19:01

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