Smoke comes in though the air vent when the heat is on. there is no heat though, its a 1994 buick park ave 124,000 miles what could it be? what can I do to fix it?

does it have a sweet smell to it at all? i think your heater core may have a lot to do with the problem i had a blue car that did that to me and it would put out a ton of smoke.to where i could not even see to drive down the road.i think it could be either the heater core OR the thermostat not opening all the way but either way you need to try to get it to a shop and have it fixed asap before anything really major goes wrong other than what already is wrong does it have a sweet smell to it at all? i think your heater core may have a lot to do with the problem i had a blue car that did that to me and it would put out a ton of smoke.to where i could not even see to drive down the road.i think it could be either the heater core OR the thermostat not opening all the way but either way you need to try to get it to a shop and have it fixed asap before anything really major goes wrong other than what already is wrong