You have a coolant leak in your heater core behind the dashboard of your car. The sweet smell and the fog is the coolant from the engine being blown out the vents into the car interior.
There really is no easy way to fix this; the heater core needs to be replaced. This is very labor intensive so only advanced do-it-yourselfers should attempt it. Take it to a mechanic.
Since this is an engine coolant leak, it can drain your radiator and cause your engine to overheat if too much coolant leaks out. Also, the leak can get bad enough you start getting puddles in the floor of the passenger compartment. One can bypass the heater core at the firewall (in the engine compartment), however this means no heat in the winter for passengers.
You need a cooling system leakdown test. Then check the usual suspects. You have coolant in the heater case.
some applications, this can be hose connections.
also, some offer a stronger part. for the heater.
wear your roller blading knee pads.
have fun with all them little screws.
Get your procedure at the library to see if it is really something you want to tackle and price it at the dealer because they have the most experience.
Then decide .
You did not say what car or truck it is, so cant really be specific.
Make sure you don't have to reclaim your A/C refrigerant and remove your evap case for access to the heater.
That can take tools you dont want to buy and machines you dont have.
You have a coolant leak in the heater core.
You have a leak in your cooling system. The sweet smell is the odor of anti freeze.
It's possible that your engine moved enough to crack one of the pipes on your heater core and now it's leaking. That would be my guess. What you smell is antifreeze.
You need to take the car to a pro to get it fixed, asap.
I had slid on ice and hit a curb, my heat was on full blast and was working fine for half the day then I shut off the car, let it sit for roughly an hr and started it back up and then it was blowing smoke and a sweet smelling odor from the defroster. I do have a minor coolant leak also but I've had the leak for a while.
