What was found
CAB CONT "ZONE TEMP" ILLUMINATED, COMPLIED WITH QRH PROCEDURE AND "ZONE TEMP" RESET WITH MASTER CAUTION RESET. CAB CONT AT FULL WARM PRODUCED 10 DEGREES C ON SUPPLY DUCT TEMP, COCKPIT WAS COLD. CONT CAB FWD CAB & AFT CAB ALL SELECTED OFF. COCKPIT TEMP STABILIZED. SUPPLY DUCT TEMP IS 24 DEGREES C. DUCT PRESSURE SPLIT "L" IS 21 PSI AND "R" IS 40. GROUNDED - YES. TRANSFERED DUCT PRESSURE SPLIT "L" IS 25PSI , "R" IS 40PSI TO LOG PG # 60232347 36205 08/19/21 PERFORMED P2TC BITE REF B737-900 AMM 21-61-00, #2 CONTROL FAULTED CONTROL CABIN TRIM AIR VALVE . FAULT RESET ON VERIFY BUT VALVE MOTOR SOUNDED WEAK AND INTERMITTENT. DUE TO HISTORY , REMOVED AND REPLACED CONTROL CABIN TRIM AIR VALVE REF AMM 21-61-21. VALVE OP CHECKS GOOD , REQUIRES LEAK CHECK REF AMM 21-61-21. COMPLETED INSTALL OF THE CONTROL CABIN TRIM AIR VALVE REF AMM 21-61-21-400-801 LEAK TEST GOOD.