or doesn't blow as hard, you probably need to clean or replace the
HVAC system's cabin air filter element.
Getting to the filter is a little more involved than our Toyota
Corolla where you just have to drop the glove box, but the whole
process only takes about 15-30 minutes. You'll need a Phillips head
screwdriver and a small flathead screwdriver.
Here's the guide -
formatting link
I'd recommend getting the Purolator brand replacement filter since I
was able to verify the correct part number for the 07-12 Altima on
both Amazon and Advance Auto Parts.
If the old filter isn't too dirty save yourself some money and just
tap out the bugs/leaves/dirt and blow out the dust with a shop
vacuum.
-Paul