A while back my wife mentioned that smoke was coming from the front vents after a bit of driving with the A/C on. This does not happen regularly and the Freeon levels do not change. The other day, I witnessed this myself. There was no freeon odor - it didn't have an odor much at all. Then after about five minutes, it just went away. If freeon was leaking out, my A/C today would not be working, but as far as I can tell, everything still seems to work. To answer some basic questions: 1. No it was not smokey outside 2. No I do not smoke 3. No, it was at 73-degrees, not full cold when this happened. Yes, we were in the car for only a few minutes after leaving the mall (which is approx 30 miles from my house) On the way there, cold A/C, no smoke. -TiM
After running the A/C awhile do you see a puddle under the car while it is parked. It is normal for this to happen. I am speculating that the evaporator drain is clogged or draining slow. The water is collecting and what you see is frost blowing out the vent. If it is smoke it should rise as it comes out the vent due to it being warm. If is frost is will sink slightly as it comes out of the vent.
Along this lines of what @mikes said, when the A/C first starts, if it is really humid inside the vehicle, you can get fog coming out of the vents until the A/C brings the humidity down. This is because as the cold air coming off of the A/C hits the interior air, it is condensed, making fog. This probably lasts for about two to three minutes and then all is fine. Could be a bit longer if it's really humid. I used to see this all the time when I lived in the State of Georgia.
You did not decribe the smoke. what colour? Smell? You can tell a lot from these details. Did you use heater or cooler? I suggest changing the a/c compressor. They are semi consumable and not expensive and wear out after some time.