To be honest, I'm not aware of Cadillac using that (mainly import) feature. GM usually uses recirc. air only when "MAX" A/C is selected (manually or automatically by the computer) in an effort to more quickly cool off the interior. For years, I've had people tell me that they thought that selecting "MAX" A/C caused an even higher blower speed than "HI" does. Actually, the extra noise heard when selecting "MAX" is only due to the recirc vent opening and then allowing the occupants to hear the fan more readily. As soon as "MAX" is de-selected, interior noise level reduces due to the vent closing, not due to a reduction in fan speed. Either way, selecting "RECIRC" on a system that provides the seperate setting only increases the percentage if interior air into the system. It DOES NOT eliminate outside air being brought in. By law, all OEMs must have a constant flow of outside air into the car. Even when the blower is "OFF", you are still getting outside air into your car.