What was found
AIRCRAFT WAS GROUNDED: THE ACFT DIVERTED TO MCO DUE TO THE FLT CREW REPORTING THAT DURING PUSH BACK FLT ATTENDANT REPORTED ODD SMELL IN AFT CABIN, BUT FELT OK. ALL OTHER FLT ATTENDANTS WERE OK AS WELL. NO UNUSUAL SMELL IN THE FLT DECK. DURING CLIMB OUT ABOVE FL 280 FLT ATTENDANTS REPORTED ODD SMELL & ODOR INCREASING. A MUSTY/SWEET ODOR. REPORTS OF HEADACHES & COUGHING. ACFT LANDED SAFELY AT MCO & TAXIED TO THE GATE UNDER ITS OWN POWER. MAINTENANCE FOUND THE APU TO BE THE CAUSE OF THE ODOR AND REPLACED IT PER TASK CARD 26L31049003. A DECONTAMINATION OF THE ENVIRONMENTAL CONTROL SYSTEM WAS ACCOMPLISHED PER TASK CARD 26L00021014. A SATISFACTORY LEAK / OPERATIONAL CHECK WAS ACCOMPLISHED WITH NO ODORS NOTED.