Should the Car Air Conditioner Use Internal or External Circulation?

[Moreira]

Whether to use internal or external circulation for the car air conditioner depends on different situations: 1. Use internal circulation during traffic jams to prevent polluted air from outside from entering the cabin; 2. Use external circulation during long-distance driving to allow fresh air from outside to enter the cabin, avoiding low oxygen levels inside. The function of internal circulation is to promptly and effectively block external dust and harmful gases from entering the car, with faster cooling and heating effects. The function of external circulation is to supplement fresh air, maintaining air circulation between the inside and outside of the car, which helps keep the air inside the cabin clean. The internal circulation of the car air conditioner is located below the front dashboard in the driver's compartment, while the external circulation is located below the windshield on the passenger side of the engine compartment.

[KingstonAnn]

When I first started driving, I used to struggle with this issue too, but now I've figured it out: In summer, if you want to cool down the car quickly with AC, just press the recirculation button—it recycles the cool air inside, making cooling faster and more fuel-efficient. However, on long trips or rainy days, be careful not to keep recirculation on for more than twenty minutes continuously, as the windshield can fog up easily. That's when you should switch to fresh air mode to defog. Personally, once the car's temperature drops, I switch to fresh air mode on highways—it prevents stuffiness and keeps the air fresh. If stuck in traffic or passing by chemical plants, I immediately switch back to recirculation to keep exhaust fumes and odors out.

[JeffreyLee]

Last week when I took my child out, I kept the car's AC on recirculation mode the whole time. My child ended up feeling dizzy and nauseous, which reminded me of what I read in professional manuals: prolonged recirculation over 30 minutes can cause carbon dioxide levels to skyrocket. Now I've learned to use the auto mode (the arrow icon with the AUTO button) by default, letting the system balance between fresh air and recirculation automatically. During smoggy days on the school run, I long-press the recirculation button to lock in air purification. Five minutes before parking for lunch, I switch to fresh air mode to dissipate heat—this way the car won't feel like a sauna when we return.

[SebastianLynn]

Last time I drove my bestie's new energy vehicle, I learned a clever trick: turning on the air recirculation during traffic jams can save 10% of battery power, but prolonged AC use might feel stuffy. My current operating mantra is 'long-distance trips use external circulation, traffic jams use internal circulation.' I remember once driving on the highway with windows down—the wind noise was too loud and it wasted fuel. Closing the windows and switching to external circulation made it both quiet and fuel-efficient. If there's heavy smoke or perfume smell in the car, just turn on external circulation for five minutes to clear it out.

[Prim]

Last year at the repair shop, the mechanic explained the principle: the fresh air intake for the external circulation is located below the windshield. So remember to switch to internal circulation during heavy rain to prevent water from flowing back into the blower. Now, I check the cabin air filter every time I wash the car—if it's clogged, even using external circulation feels stuffy. When I first got the new car, I drove on the highway with external circulation to dissipate the formaldehyde smell. By the way, turning on external circulation before shutting off the AC during rest stops at service areas can help prevent mold in the AC ducts.

[AxelFitz]

In early spring up north, pollen allergies get really bad. I keep the car on full recirculation with air purifier to keep my nose comfortable. But when taking sharp mountain curves, I always feel ear pressure with recirculation on. Veteran drivers told me it's caused by air pressure difference, and switching to fresh air mode helps. Now I've developed habits: using fresh air with heater for fastest defogging in winter, and just opening the sunroof in spring/autumn to avoid circulation dilemmas. Smell earthy odor when first turning on AC? That's dust accumulated at the fresh air intake - time for cleaning!