Messing with my 03 4.4i yesterday and it got really warm, really quickly in the car (I was wearing a heavy outside jacket) and hit the 'Max AC' button on the auto climate control.
Nada...nothing....zip !
Hmmm... fiddled some more, regular AC works, everyhting else works but no max AC.
Ah well, perhaps I disturbed something when I removed the panel to add the aux input.
On a whim, I actually checked the manual and to my surprise found the following "Max AC function is in-operative if outside air temp is 41* or less"
Ahhhh... 38 * outside so it makes sense, most folks don't need max AC but there you have it, MAX AC shuts down at 41* or less ... we learn something everyday