A/C steaming from vents?

If it smells sweet it is likely a leaking heater core in the dash. The system works by running air over the heater core and then over the AC EVAP core. So even a small leak in the heater core would travel through the system and show up as steam. If it has overheated the leak may be losing enough coolant to cause air in the system and then it overheats. So does the steam smell sweet and is it leaving any film on the glass? If it is either one it's got a leak. The only solution is replacing the heater core. For that you have to remove the instrument panel to get to the HVAC housing.