A GULFSTREAM 11 IN CLB AT 14000 FT DECLARED AN EMER AND RETURNED TO THE DEP ARPT DUE TO PAX RPTING SMOKE IN THE CABIN.

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CLBING OUT ON RADAR VECTORS TO SID; PAX NOTED SMOKE IN THE CABIN. IT WAS VERIFIED VISUALLY BY BOTH PLTS. RAM AIR AND EMER PRESSURIZATION WERE SELECTED; ATC WAS NOTIFIED; AND FOLLOW-UP CHKLIST WAS ACCOMPLISHED FOR SMOKE REMOVAL; AND THE ACFT RETURNED TO ZZZ FOR AN UNEVENTFUL LNDG. THE SMOKE IMMEDIATELY DISSIPATED WITH NO FURTHER INFLOW. MAINT INVESTIGATED AND DISCOVERED BOTH MANUAL TEMPERATURE CONTROL VALVES; IN THE AFT BAGGAGE COMPARTMENT; WERE SET TO FULL HOT. THESE CONTROL VALVES OVERRIDE THE INPUTS IN THE REMAINDER OF THE SYSTEM; SO THE PLTS HAD NO CTL OF THE AIR BEING SENT THROUGH THE DUCT SYSTEM; AND THE DUCTS HAD OVERHEATED AND WERE CREATING THE SMOKE. NO DAMAGE WAS DISCOVERED; THE VALVES WERE RESET TO THEIR CTR/OFF POSITION; THE SYSTEM WAS GND CHKED; AND A SUBSEQUENT FLT WAS ACCOMPLISHED WITH NO PROBS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE FOLLOWING; THESE AFT CARGO COMPARTMENT'S MECHANICALLY OPERATED VALVES ARE ONLY INSTALLED IN THE GULFSTREAM 11 AND NORMALLY SET TO CTR/OFF POSITION. THIS AIRPLANE HAD JUST BEEN RELEASED FROM MAINT AND WAS ON ITS FIRST FLT. THE VALVES' SETTINGS ARE NOT INCLUDED IN THE PREFLT INSPECTIONS AND IT IS BELIEVED THE SETTING OF THESE TWO VALVES TO FULL HOT WAS DONE WHILE IN MAINT. THESE VALVES WHEN SET IN THE FULL HOT POSITION WILL OVERRIDE THE TEMP INPUTS TO THE AIR CONDITIONING SYSTEM. WHILE SET TO FULL HOT; THE DUCTING OVERHEATED CREATING THE SMELL AND SMOKE. THE RPTR HAS NEVER EXPERIENCED THESE VALVES SET TO FULL HOT AND THEY WERE NOT AWARE OF THE POSSIBILITY OF DUCT OVERHEATING.