On my car ('98 S70) the AC compressor will run if the button is on until the outside air temp gets to around 40. The AC compressor is shut off by the system below this temperature. This is according to the owners manual.

Another neat feature of the climate control I discovered by accident: I set the ECC "recirc" feature to the timer mode. This is outlined in the owners manual. The recirc mode is then on a limited timer and will automatically switch back to "fresh" after a period of time according to conditions. This prevents you from leaving the AC in "recirc" mode for extended periods of time. After that, any time you manually select "recirc" again, it will automatically change back to "fresh". (Usually in 5-10 miunutes). Anyway, after setting it up this way, I noticed when it is very hot out and the car interior is also super hot, the ECC will automatically select and start up in the system "recirc" mode! (Just like Dad's Caddy!) When the car cools down a bit, it will switch to "fresh"! If the car is not super hot, or if the windows were open so the car is cool, it will start in "fresh" mode as usual.

Nice feature that is not documented anywhere.