If your vehicle is showing chemical or gunpowder smell in the cabin without a crash, here are the most likely causes and the parts you'll need to fix each one.
The blower motor resistor controls the HVAC fan speeds and gets extremely hot. If the resistor fails or its plastic wiring connector melts, it produces a strong acrid, ozone, or gunpowder-like electrical burning smell through the vents.
A small leak in the heater core allows hot engine coolant to vaporize into the cabin's ventilation system. This creates a sweet, pungent chemical smell, often accompanied by a greasy film on the inside of the windshield.
If the A/C evaporator develops a leak, refrigerant and PAG oil escape directly into the HVAC system. This causes a distinct chemical, ether-like, or sweet odor from the vents when the climate control is on.
A failed voltage regulator can cause the alternator to overcharge the 12V battery. This causes the battery acid to boil and vent sulfuric gas into the cowl area, which smells like harsh chemicals, rotten eggs, or sulfur.
Seatbelt pretensioners use small pyrotechnic charges to pull the belts tight during a crash. A severe pothole, electrical short, or faulty sensor can trigger them without deploying the airbags, leaving a literal gunpowder smell in the cabin.
A severe short circuit or water intrusion can blow internal capacitors inside a major computer module. Blown capacitors release a smell exactly like gunpowder or burnt ozone.