Sometimes there is a fog like/vaporish looking stuff coming thru the vents

If the heater core is leaking you'll find an oily residue on the windshield after using the defroster. That's from the antifreeze in the coolant. It usually smells kind of sweet but it was reformulated years ago to make it bitter-tasting so pets won't drink it and become sick. Look for a small puddle on the ground where you park, in about the area under the front passenger's feet. There's a drain tube to drain off the condensation when the air conditioning is running. That should be water dripping there. If you find antifreeze, the heater core is leaking. The level will be slowly going down in he reservoir under the hood too.

Refrigerant can also be leaking from the "evaporator" in the dash but it won't take long before the air conditioning will stop working. Breathing refrigerant is only harmful in that it displaces air. The air blowing from the vents must never get below about 40 degrees or that condensation will freeze into a block of ice and stop the cooling action. The system is regulated to prevent that. Normal air coming from the vents with the air conditioning on is around 60 degrees. If the air is considerably colder than that, you may indeed be feeling the vaporizing, (leaking) refrigerant which can get REAL cold and cause frostbite. That will only occur for a short time before the system is discharged and will stop working.