I just bought an 04 Z71 with the automatic dual climate control. I was reading the owners manual while waiting at the dealer, and read that when using the AUTO feature to keep your temp controlled automatically, the compressor will run when outside temps are above 40F. Even if you turn the AC of and the snowflake is not showing on the display, the compressor will still run "in order to dehumidify the air" inside the truck. This is noteworthy because according to my DIC, the fuel milage kept by the computer is immediatelly affected by approx 2 - 2.5mpg. Much different than my 98 where I noticed little to nofuel milage change when using the AC. Unless I was doing all city driving my 98 K2500 stayed at 15 mpg.