Smoke and it smells comes out of vents when ac on nissan altima

Their must be some oil stored somewhere and it is dripping on your exhaust manifold,but never pressure wash your engine, could cause worse problems,in time the smell will go away,just be patient.It will burn off in time.

The speed control of your fan has resisters that are in the venting system to blow air on them to keep them cool. If they overheat and or burn you will lose your low and medium speeds of the fan. If you run the fan at full see if the smell goes away. Your engine could be burning oil on the outside of the engine block, make sure that the weatherstrip where your hood meets the fresh air intake grill is sealing tight.

I could be that the evaporator core started to freeze up and what you saw was the steam coming off of that.

Check you cabin filter it is under hood on pass side near wiper blades
If the blower motor is running fine and no smell from there.

no it has a closed system so no smell of petrol so their is something wrong with the suction pump and the pipes that come from teh engine compartment

something near the a/c vent (under your hood) started to burn or burnt something stuck in there like leaves or plastic etc. check your lines and fuels, make sure nothing's leaking or dried up.

Perhaps the Blower Motor for the Heat/AC, is going bad.

Oil is leaking getting into the cylinders which is being burnt which is causing the white smoke from the exhaust. You might have compression problems or worn valves.

I've had mice in my Nissan PU and actually caught one in a trap set on the floorboard; so I know they can get inside. They also knocked some of the fiberglass insulation into the blower motor so it vibrated as it was no longer balanced. You could have a dead one in your blower. Mine was easily accessible from under the passenger side under the dash. Three screws and the motor dropped so I could clean out the fiberglass.

white smoke is water
blue smoke is oil.
nest time try and smell the white smoke see if it smells sweet?
if it does its antifreeze.
and also black smoke is fuel (like a leaky injector )
hope this helps
paul