Offgassing dash pad ??!?
The heater core could be leaking. I had an incident with a truck i owned back in the early 90's. I was doing a lot of windshield time & I began to feel off, not to the point of being sick, just didn't feel well. I finally went to the doctor & he scheduled blood test & discovered glycol in the test. He asked if I had been exposed to any coolant, which I hadn't to my knowledge. I had noticed a fine mist coming from the passenger side AC vent but wrote it off as just condensation. I took the truck to a reputable shop & they pressure tested the coolant system overnight. I leaked down to zero & they looked up into the heater core. Lo & behold, it had a minute pin hole & the coolant was permeating the cab as a fine mist while I was driving. The heater core was replaced & I was put on medication to help alleviate the glycol from my system. Just a heads up, because the leak "may not" be big enough to leak onto the carpet & glycol poisoning can lead to a "LOT" of health problems including organ failure.