What was found
(CAN) DURING TAXI TO THE GATE, FLIGHT CREW RECEIVED A "SMOKE TOILET" CAUTION MESSAGE SHORTLY FOLLOWED BY A "RT PACK HI TEMP" CAUTION MESSAGE. THE F/A NOTICED LIGHT SMOKE AND A BURNING ODOR IN THE CABIN NEAR THE LAVATORY, LAV AREA. AS A PRECAUTIONARY MEASURE, SHE DISCHARGED A FIRE EXTINGUISHER INSIDE THE LAV COMPARTMENT. THE ACFT CONTINUED TO THE GATE AND THE PASSENGERS DEPLANED WITHOUT FURTHER INCIDENT. DURING TROUBLESHOOTING, MAINTENANCE FOUND THAT THE FLAPPERS, 2 OF THE RT PACK RAM AIR CHECK VALVE, IPC 21-52-00-01-035, WERE MISSING. THE FLAPPERS WERE FOUND AT THE HEAT EXCHANGER, RESTRICTING THE COOLING AIR FLOW. THE CHECK VALVE WAS REPLACED, THE PACK SYSTEM TESTED AND THE ACFT RETURNED INTO SERVICE.