Yesterday while driving home, I decided to use my automatic climate control. I set it to 72 and let the system take over. After a few minutes I noticed that steam or smoke would appear to flow out of the vents in cycles (visible for a minute, then it would go away), and that it had a sweet smell. I also noticed that when I set the climate control to coldest, it would go away. I started thinking that the smoke was linked to when the heater came on to temper the AC as the system was controlling for 72 degrees.

Based on that assumption, I scoured the boards for answers, and so far I've come up with a possible leaky heater core; the idea being when the heater cycles on during automatic control, coolant escapes, evaporates, and gets blown into the cabin. There isn't enough mist to fog up my windows. And my AC appears to be working very well, it's ice cold when I've set it to max. However, I've also noticed no drop in my coolant levels after 1000 miles, so if there's a leak, it's slight.

Do I have this diagnosis right, or is there another possibility?