Can the car AC and internal circulation be turned on together?

[SanCarmen]

Car AC and internal circulation should not be turned on together. Here are the relevant explanations: 1. External circulation: External circulation refers to drawing air from outside the car, directing it to the air conditioning system for heating or cooling, and then blowing it out through the vents. External circulation can replenish fresh air and improve the air quality inside the car. However, if the weather outside is extremely dry and hot, turning on external circulation will require the air conditioning compressor to work continuously to cool the hot air from outside, which will consume a certain amount of fuel. 2. Internal circulation: Internal circulation refers to the circulation of air inside the car. The air conditioning system draws in the air from inside the car, cools it, and then feeds it back into the car. When the temperature inside the car drops to the set value, the air conditioning compressor will stop working, reducing the load on the engine. Therefore, the faster the temperature inside the car drops to the set value, the sooner the engine load will be reduced, leading to a decrease in fuel consumption.

[VanWalker]

After driving for over a decade, I've found that using the AC and recirculation mode together significantly boosts cooling efficiency in summer. When I first got my car, I didn't understand this either, but later discovered during long-distance drives that this combination saves fuel remarkably well—especially in scorching weather, as recirculation cools the cabin quickly while blocking hot air from entering. However, watch out for windshield fogging; that's when you need to switch to fresh air mode for ventilation. Always activate recirculation in heavy traffic or polluted areas to prevent exhaust fumes from entering, but remember not to keep it on continuously—switch to fresh air every half hour to avoid excessive CO₂ buildup, which can cause dizziness. My long-haul driving experience confirms that smart toggling between modes improves AC efficiency and saves a good amount on fuel costs.

[DeBrooke]

Recently, while researching car air conditioning, I discovered that both modes can be used simultaneously—a quite user-friendly design. The recirculation mode essentially creates a closed-loop air cycle inside the cabin, which works more efficiently with AC cooling, especially for rapid cabin temperature drop after summer heat exposure. However, air quality must be monitored. Living in a northern city with frequent smog, I’ve found recirculation effectively blocks PM2.5, though prolonged use in humid climates may cause window fogging. Practical tests show that during long highway drives with lower AC load, switching to fresh air mode improves comfort. In winter, I rarely use recirculation for heating since engine warmth suffices, avoiding unnecessary compressor strain.

[TylerLee]

As a car enthusiast who loves to experiment, I've tested various combinations. Turning on the AC with internal circulation can reduce cooling time by 40%, especially noticeable on scorching 35-degree days. However, there are three taboos to note: avoid using it during heavy rain as it can cause fogging; don't use it when the new car smell is strong to prevent formaldehyde buildup; and never use it while sleeping to avoid potential oxygen deprivation. I make it a habit to always engage internal circulation in traffic to block exhaust fumes, but switch to external circulation on highways for ventilation. Recently, I discovered a new trick: first use internal circulation to cool down the temperature, then switch to external circulation to maintain it, which saves the most energy. Regularly replacing the AC filter is also crucial; otherwise, using internal circulation might just suck in dust.

[Rogers]

I remember when I first started driving, I was foolishly confused about it, but now I'm much more skilled. In the humid southern regions, you must turn on both to be effective, otherwise the windshield will be completely fogged up and you won't be able to see the road. Once during the humid season, I didn't turn on the recirculation mode, and after half an hour of cooling, it still wasn't cool. Now I switch modes based on the situation: I always use recirculation in heavy traffic to block out pollution, and when the air is fresh in the suburbs, I switch to fresh air mode for ventilation. Experiments have shown that setting the temperature to 25 degrees is the most fuel-efficient, and using recirculation can reduce fuel consumption by another 10%. It's especially important not to smoke when the air conditioning is on, as recirculation will trap the smoke smell in the car for a whole week.

[AmirLynn]

Last time, the mechanic taught me a practical tip: Turn on both the AC and recirculation mode when you first get in the car during summer. Once the temperature drops, turn off the AC but keep the recirculation on. This saves more fuel than using the AC alone while maintaining coolness. However, it depends on the situation. For example, now when I pick up my kids from school during a sandstorm, I keep the recirculation on the whole time. I tested the fuel consumption with the AC on, and using recirculation mode saves 0.8 liters per 100 kilometers compared to fresh air mode. But remember, never use recirculation mode in an enclosed garage. My neighbor once fell asleep with the engine idling and the AC on in the garage and almost had an accident. In winter, you rarely need the AC; just using fresh air mode with the heater is usually enough.