uhh, not exactly. the a/c system is a sealed system (just like your fridge) containing R134 and lubrication oil. the compressor compresses the R134 so it's at a higher pressure to expand and cool.

you never compress the outside air, it just flows through the evaporator core. the cold evaporator core causes the moisture in the outside air to condense on it, thus drying the air that enters the cabin. the condensate on the evap core runs out underneath the car, which is why your car drips water when your a/c is on.

also, if you put the temp setting on mid-cool, it doesn't cause the compressor to run less frequently. the temp is adjusted with a blend door that regulates the mixing of cold air from the evap core with hot air from the heater core. high and low pressure switches control the cycling of the a/c compressor.

 

I figure the lack of exhaust smell does not mean inside air is healthier. Your car can be full of gases you do not smell that creep in from the engine and fluids. Even the surfaces of all the materials in your car give off gases, especially if the car is in the sun. That’s one reason why the inside of the windshield gets dirty over time.

More importantly, there is the animal in your car that takes in oxygen and exhales carbon dioxide. If your car really didn’t bring in outside air, the oxygen level would slowly go down as the carbon dioxide displaces it. Then you get sleepy and run off the road and hit something.

So, in order to have healthy air, I always have it set to bring in outside air. Well, I set to recirculation for a 5 mile stretch between LA and SF on I5 near Harris Ranch.