Front heater core is in the dash, the rear heater core is all the way in the back of the vehicle. If you have steam coming out of the dash vents, the front HC is leaking. If you have steam coming out of the rear heater vents, then the rear core is leaking.
you need a new heater core
your heater core is leaking anitfreeze! heatercoreleaks antifreeze into the heater & ac vents causing a burnt spell & oily film on the front window.
Either the a/c system is freezing up or you have a leaking heater core.............
This means that you have either an issue with a vacuum line or one of the a/c - heater doors behind the dash is not working correctly and you need to start off at the a/c - heater controller to check that all positions are working...........
smoky mist coming from the heater vents.
The heater may not be on - but the fan still blows air through the vents when they're open !
There are heater doors on the heat blower box that direct the path of the heat. Apparently the heater door to the floor vents is stuck closed.
Check for a broken vacuum line by the battery. These lines get brittle and break with age.
There is no heater matrix for the back air vents, only and evaporator for the A/C. My suburban always blowed cold until I added an extra rear heater matrix.
heater fan broken.
1st bet: Does it smell like antifreeze? Leaky heater core. 2nd bet: Worse after rain or car wash? Leak under cowl vents (the vents in front of the windshield. Good luck!