No, air conditioners don't bring in fresh air from outside. This is not how they were designed. What actually happens is that the air conditioner uses a fan to draw air into the interior of the unit and disperse it through a structure. Air conditioners are never designed to bring in air from outside the house.
They are considered a sealed system in the sense that they will only work in the air within the ecosystem of the building in which they are installed. In the past, there was a big industry around evaporative air coolers and all the supplies you needed to set up an evaporative air conditioner outside the windows and the house. But those types of air conditioners have now taken a backseat. However, you can still find grilles on some models that are designed to introduce air into the cooling process.
These grilles are used to draw air into the back of the unit and help ventilate the condenser coils. Unvented air conditioners don't require a way to vent out the warm air that comes from the rear of the unit. And while they don't require any way to drain them, they do require a water source that is connected directly or added manually. Whenever you find an air conditioner that says it doesn't need an exhaust or doesn't have ventilation, you'll know that you're looking for an air conditioner that needs a water supply.
In some cases, window or water-based systems may not be practical for certain areas. Therefore, portable and practical aren't exactly interchangeable when it comes to air conditioning. Portable units don't need any water source, don't expel hot air from the rear, but must be emptied of water when not in use. In simpler words, window air conditioners don't draw fresh air from outside.
However, they filter, cool and recirculate the air inside your home. Some of these ACs offer a vent lever option that allows fresh air to enter when needed. This can be incredibly relaxing if your area is suffering from polluted air due to wildfires or other environmental pollution. If turned on, the fresh air vent located on the outside of the unit (the part that is outside) will open.
Split system air conditioning usually uses heat pumps and part of the system is located outside the house, but it does not absorb outside air. Outdoor air enters the system from an inlet that is usually located next to the boiler, but sometimes it is its own independent system. Its main operational purpose of cooling the air in your home is not achieved by moving cold air indoors, but by expelling unwanted heat. The most popular type of unvented AC is called a “swamp cooler” or “no ventilation” air conditioner or “no exhaust” AC.
The basic premise of this type of window cooler is to extract outdoor air onto absorption pads that have been soaked in water and cause water-cooled air to enter the room. Window ACs only work with indoor air, cooling small amounts at a time by reducing warm air that filters around holes in the machine and cold air that escapes through those holes. This helps save money on electricity and makes sure that your unit won't have to work as hard. If your home's indoor air is warm or humid, spring and fall are great times to open up your window AC's vent lever and let some fresh air in.
In addition, these ACs cannot remove smoke particles from the air since they are too microscopic for them to filter out. To sum up, window ACs don't draw fresh outdoor air into your home; they only recirculate indoor air. Portable units don't need any water source but must be emptied of water when not in use and have a large hose that must be hung across the room to expel warm air created during cooling.
