91 l98 auto, electronic ac control, never had a part replaced or go bad (beside brakes and tune-ups), I've had her for 7 years and 130K fun miles:)(sorry, it's long)

When the car reaches operating temp and you select heat for the feet:) I can't breath. Some sort of smell/odor makes it very difficult to breath. It's similar to burning dust (you know the smell when you turn the heat on for the first time each year in the house), but is so strong I have to roll the window down in order to breath (I've tried running the heat for 20min to see if it goes away, and it doesn't). I'm going on 2 years with this problem and it's getting worse. If I turn on defrost or ac vents, no smell. I can breath fine.

The odor does not smell like exhaust fumes, but I can't guarantee it's dust (again extremely strong that does not go away)...(Could be similar to a burning electrical smell, but no electrical problems)

I smell a faint coolant smell outside the car. No wet carpet. I know there is a slight intake coolant leak on the drivers side towards the firewall. I assume this is where the coolant smell is coming from, but who knows (I will be doing a rebuild in the coming months that will address this)

So, my best guess is to take it to the dealership explain the issue and pay for someone to replace the heater core and see if this fixes the issue (I researched all the possibilities of pin hole leaks, to leaking heater hoses etc. that could cause issues with coolant smells). I'm not convinced this is my problem, so that's why I'm posting.

Thoughts....

 

You may be getting a little coolant onto the heater wires inside the blower system.

 

Sounds good. Thanks

 

Coolant is fairly obvious and if you're only getting it with heat, doubt it's the a/c clutch (when they slip the smell is pretty obnoxious) or anything in the air intake or the blower motor. Mold can build up around the evaporator - especially if it's been leaking or the foam filter on the inlet side can disentigrate and work it's way into the ductwork. If it's soaked in a/c oil, it can adhere to the ductwork. You will also get a few pieces blowing out the a/c vents every now and then, so if you've experienced that, that could be the problem. Absent those things, my guess would be that something has gotten into the lower ducts (field mice, if common to your area, can be a problem) or there is something on the carpet that emits the odor when heated. To check the carpet, take a hair dryer to it and see if the odor comes back.

 

Thanks for the info.