Hot/burning coolant smells sweet like pancake syrup - it doesn't smell like anything burning. The most you'll get from a bad heater core is excess condensation on the inside of the windshield which doesn't wipe off easily, and unless it's leaking onto an electrical component that's shorting out which just happens to be in the air stream, so you won't get "smoke" unless the coolant is burning.

If you want to see if it's your heater core, lift up your carpet towards the front of your vehicle - if it's wet, you've got a busted heater core.

If your defrost won't get hot, check your monovalve & aux heat pump.

__________________
A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.