As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
"ACM OHEAT" ANNUNCIATOR WITH ASSOCIATED FLASHING CAUTION LIGHT ILLUMINATED SHORTLY AFTER TAKE-OFF. CREW SMELLED FUMES IN THE COCKPIT. EMERGENCY DECLARED AND AIRCRAFT RETURNED TO DEPARTURE AIRPORT. LANDING WAS UNEVENTFUL. MAINTENANCE REPLACED THE ECU LOW LIMIT BYPASS VALVE DUE TO STICKING AND WATER SEPARATOR CONDENSER. PERFORMED ENGINE RUNS AND GROUND OPERATIONAL CHECKS WERE GOOD. AIRCRAFT WAS RETURNED TO SERVICE.