Most people immediately hit this button when they enter their hot car on a warm day. Many simply leave it on all the time. That’s the “Recirculate” button. It causes your ventilation system to close the outside air intakes, and simply recirculate the existing air in the car thereby not allowing foul air from outside pollute the air in the car.
When people press this button, they usually hear more fan noise in the car and assume that this means their A/C system is moving more air or working harder to make it cooler – not absolutely true.
By pressing this button with the A/C on, your car is forced to cool the hotter air inside the cabin, instead of recirculating and cooling outside fresh air. This increases the time it takes to cool off the interior of the car. It also doesn’t help push out the stale hot air using the flow-through ventilation system.
You only activate this switch once the car is initially cooled off. Not immediately when entering a warm vehicle.
This other button allows outside air to flow in as it opens up the outside air intake vents which may be the better option when just entering a hot car. It may be better to switch to circulation in areas that may have bad odours in the air as it would not allow the foul smell to come visiting inside the car.