Check for a line leak to your heater core or a leak in the heater core it self. Usually it is under the dash on passinger side.
Antifreeze will be leaking in the floorboard on the passenger side, there will be a smell of antifreeze through the vents.
heater core
If antifreeze is filtering through your ac vents, other toxins could also be coming through. Don't take chances; see a mechanic.
the heater core may be plugged up
i believe the heater core is leaking, a small pin hole leak can generate a lot of smell.
heater core is shot and you have to get a new one
The possible explanation for the smell may be that the heater core in the vehicle has a slight leak, therefore the smell of evaporating antifreeze will come through the vents until it is all dried up. Solution is to take the car to a garage and get the heater core replaced.
heater core, tough job.take it to a qualified auto technician
The "antifreeze smell out the AC vents" would mean only one thing, you have a small leak in the heater core.
The heater coil probably has a leak causing steam and vaporized antifreeze to be released into the vents. Is it using coolant?
Most of the time it is caused by a hole in the heater core, do you smell a sweet smell? The sweet smell would be the antifreeze.
More than likely the heater core is leaking.