Read the manual... Checked another car.
Below is what the handbook says regarding the AC. Quite simple really. Not what youy would call rocket science.
Air conditioner button (if so equipped)
The button is provided only on vehicles equipped
with an air conditioner.
Start the engine, turn the fan control dial to the
desired position and push the AC button to
turn on the air conditioner. The indicator light
comes on when the air conditioner is operating.
To turn off the air conditioner, push theAC button again.
Below is the criteria for the AC to turn on and stay on.
"When the Defrost or Floor/Defrost position is selected, the air
conditioner automatically turns on (however,
the indicator light will not illuminate) if the
outside temperature is more than 36°F
(2°C). The air conditioning system will continue
to operate until the vehicle is restarted,
even if the air flow control dial is turned to a
position other than the defrost position. This
dehumidifies the air which helps defog the
windshield. The Recirculate mode automatically
turns off, allowing outside air to be drawn
into the passenger compartment to further
improve the defogging performance."
It appears that there is a programming glitch in the 2005s because the routine that is only supposed to occour when defrost is chosen is happening even when simply switching on Recirculate or the AC while on vent. I do not have to touch the air flow control dial.
I checked out another Altima with a salesman today and it did the same thing. He said the same as me. "Something's wrong".
If I am driving with my fresh air venting and come up behind a smog mobile, I can not simply change to Recirculate and switch back after I pass it. If I was to do that I would have to pull over to the side of the road, shut off the car and restart it to turn off the AC. By that time the Smog mobile would be passing me again!
Does this seem to you as it appears to me that there is a programming problem?