My heater has a mind of its own. When on full blast (90 degree temp setting) on the floor setting (in manual mode) and with A/C off (fresh air selection), my heater will all by itself change into center vent mode.

I have to manually change it back to the floor setting and then it will stay there (I think)

I thought it was a defect in my car, but the loaner I had did the same thing.

Anybody know why?

Now, it only does this with the heater, not the A/C, and only when full blast or close to full blast. For some reason it doesn't like to stay on the floor setting.

Inquiring minds want to know

 

I believe that even when not in Auto mode the vent selection still works automatically unless you manually change it yourself. You should be able to test this theory by turning on the A/C, turning auto off, then starting at 60 degrees, work your way up to 90. If I'm correct the vent selection should change as the temperature rises. If it does, then manually set the vent selection, then go through the temp ranges again and see if the vent selection mode changes on its own. Im going to test it when I get home to see if thats correct. I know this is how my 06 Maxima worked and the A/C system seems to be identical. My friend has an 07 Maxima and his A/C has "Full Auto" and "Auto" modes. Full auto controlled the fan speed, and vent selection. Auto only controlled vent selection. Our cars may work the same way except "Full Auto" maybe our "Auto". Im guessing as the temperature in your car rises the vent selection changes to adjust to the proper temp. Keep in mind, just a theory mine.