I have a 97 Geo Prizm that is emitting a plastic like burning smell when I turn on the heater. The smell takes a minute to start up. I took it in to a mechanic and they cleaned out the heater motor as it was filled with acorn pieces, leaves, twigs, pine needles and they cleaned the vent under the windshield. However the smell is still there and in fact is stronger when you're outside, more on the left side of the dash. I've had the heater core replaced 5 yrs ago and the signs aren't the same (with that there was white smoke and window fogged up). They also sprayed an industrial mold cleaner in the vent. Wondering if folks have thoughts on what the issue could be? Could there be more twigs etc in more unreachable places or more of an electrical issue?