As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: PILOT NOTICED ODOR AND FUMES OF UNKNOWN ORIGIN AFTER DEPARTING FROM SAT. RETURNED TO LAND AT SAT. EMERGENCY WAS DECLARED. MAINTENANCE TROUBLESHOT & COMPLETED JOB CARD 05-96-70 & FOUND RECERC HEPA FILTERS COMPLETELY FOULED & DUCTS WITH BLOCKED AND DIRTY OUTLETS. REMOVED AND REPLACED HEPA FILTERS IAW JOB CARD 1711 AND CLEANED DUCTS. RAN A/C SYSTEM WITH APU & ENGINE, NO SMELLS NOTED.