As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PRIOR TO TAKE OFF, TURNED ON THE ACFT`S AIR CONDITIONER. DURING CLIMB OUT WE SMELLED AN ELEC BURNING SMELL & ASSOCIATED GREY SMOKE COMING FROM THE NOSE OF THE ACFT. TURNED OFF THE THE AIR CONDITIONER, PERFORMED THE EMERGENCY PROCEDURE FOR SMOKE IN THE COCKPIT & LANDED BACK ON THE HELIPAD & COMPLETED THE SHUTDOWN WITHOUT ANY FURTHER INCIDENT. THE AIR CONDITIONER COMPRESSOR BELT HAD HEATED & BROKE.