Which is the external circulation of the car air conditioner

From an engineering perspective, external circulation refers to the HVAC system sourcing air externally via vents near the windscreen base. This contrasts with recirculation, which reuses cabin air. It’s mechanically simpler but less efficient for cooling/heating. Most cars, including the Ford Focus, allow manual toggling via a dashboard button (usually marked with a car icon and an arrow pointing inward).

The symbols for the external and internal circulation of the car air conditioner are easy to recognize. The buttons for external and internal circulation are usually located near the temperature and airflow control knobs. The external circulation symbol is a small car with an arrow coming in from outside the car, while the internal circulation symbol also has a small car but with the arrow inside the car. The external and internal circulation functions of the car air conditioner are features every car owner will use. When driving at high speeds and it's inconvenient to open the windows for ventilation, you can turn on the external circulation function of the air conditioner to keep the air inside the car fresh. When driving on roads with a lot of dust or in traffic jams, you can turn on the internal circulation function of the air conditioner. If external circulation is turned on during a traffic jam, the car may fill with the smell of exhaust fumes.

Using the internal and external circulation functions of the air conditioner correctly can improve comfort and benefit the health of the car's occupants. During short, low-speed trips or when there are fewer people in the car, you can choose to use either internal or external circulation. When passing near construction sites with a lot of dust, it's advisable to turn on internal circulation.

The air conditioning system needs regular cleaning and disinfection, otherwise, a large number of bacteria can grow inside the system, which can harm the health of the car's occupants. If not cleaned for a long time, the air conditioner may also produce unpleasant odors. It is recommended that car owners clean the air conditioning system at least once a year. The air conditioner has an air filter, which needs to be replaced regularly; otherwise, it may affect the performance of the air conditioner.

The external circulation mode in a car’s air conditioning system draws fresh air from outside the vehicle, rather than recirculating the existing cabin air. This is useful for improving ventilation, reducing stuffiness, or clearing fogged-up windows.

When to use external circulation:

1. Fresh air intake – Ideal for long drives to prevent drowsiness by maintaining oxygen levels.
2. Defogging windscreen – Helps clear condensation by introducing drier outside air.
3. Polluted cabin air – Useful if passengers smoke or if there’s a strong odour inside.

When to avoid it:

1. Heavy traffic or tunnels – Prevents exhaust fumes from entering.
2. Extreme heat or cold – Recirculation is more efficient for maintaining cabin temperature.

Modern systems, like those in the Tesla Model 3 or BMW iX, often automatically switch between modes based on air quality sensors.