What was found
COCKPIT AND FWD TEMP CONTROL UNRESPONSIVE IN AUTO OR MANUAL. AFT WORKS NORMAL. CYCLING TRIM AIR RESTORED PARTIAL CONTROL. PASSENGER COMPLAINED OF COLD IN FWD CABIN AND CONTINUED ADJUST IS WHEN FLT CREW RECOGNIZED LOSS OF TEMP CONTROL. ACFT GROUNDED. BITE CHECK OF PACK/ZONE TEMP CONTROLLERS OK. NO FAULTS LOGGED, INSTALLATION TEST OF TRIM AIR PRSOV FAILS. WITH COCKPIT SELECTOR IN FULL WARM AND FWD AND AFT IN FULL COLD. NO DIFFERENCE IN SUPPLY DUCT TEMPS IAW FIM 21-62/855. REPLACED TRIM AIR PRSOV. OPERATIONAL TEST PASSES IAW AMM 21-62-01/401. TECH SERVICES REQUESTS FOLLOW UP. STCV FAILED TEST. REPLACED STCV IAW MM 21-51-11. OPS CK GOOD. NO OTHER DEFECTS NOTED.