Help! Smoke coming out of the vents!
 

I was driving this morning and had the car fan on. Waited at least half an hour and then turned the a/c on. That's when I noticed smoke coming out of the a/c vents. Turned it off immediately! What's going on?

It's steam! Natural result of an A/C unit running in a humid climate.

Agree, this is moisture. The worrisome part is that you had the system off. There have been reports of odd odors coming from the A/C system, which seems to trace back to mold growth in moisture. If you simply "set it and forget it" (except in extreme situations, such as needing MAX COOL), by placing it in AUTO, and vary the temp dial as needed, you will likely have better and cleaner performance over the long run. The system, when left in AUTO, has been designed to operate as needed to keep itself dry internally. This is how the car was intended to be used. Those who override the AUTO are depriving themselves of this benefit.

I have a 2008 Mercedes GL450 and have SMOKE coming out the vents when the heating system is on. Why would this be happening?

This is typical when you have an ac drain that is clogged. You can fix it by blowing compressed air up inside the drain.

I turn the heat dial to the drivers side temperature up and no smoke. But when I turn up the heat temperature on the passenger side is when the smoke comes out of the vents. Still a clogged ac drain?

On humid days, water vapor in the air may condense and freeze inside the air conditioning evaporator. This is normal and happens on many systems. It is not Freon. Do not worry about it.

I live in Arizona where it's not humid and or freezing accurs.

I lived in AZ. Average 43% humidity. Trust me, you have it.

Perhaps humidity built up in the 1/2 prior to turning the AC on from normal respiration and perspiration. Then when the cold air started flowing it fogged up before it all had a chance to condense on the coils?

Where is the ac drain located?

underneath the car near the firewall area