What was found
CONTROL CABIN TEMP CONTROL HAD NO EFFECT ON FLIGHT DECK TEMPERATURE OFF POSITION. MAINTAINED 20 DEGREES C. NO ABNORMAL INDICATIONS ON RECALL. ACFT GROUNDED. WHILE ON DEFERRAL: FWD CABIN COMPLETELY UNRESPONSIVE IN AUTO AND MANUAL SUPPLY DUCT TEMP REMAINS AT 5 DEGREE C, REGARDLESS OF TEMP SELECTION. CONTROL CABIN COMPLETELY INOPERATIVE IN OFF POSITION TEMP READS "0" IN FULL COLD AND FULL WARM TEMP READS "0". BITE OF 1 & 2 CONTROLLERS GOOD. NO FAULTS LOGGED. CONTROL CABIN TEMP HAS NO CONTROL IN ANY POSITION. OFF GOES TO FULL COLD. TROUBLESHOT SYS IAW FIM 21-61, TASK 861. SUSPECT TRIM AIR PRSOV INOPERATIVE. PRSOV FAILS OPS CHECK IAW MM 21-62-01. TEMPERATURE IS CONTROLLABLE WITH TRIM AIR SWITCH OFF. CLEANED ALL 3 CABIN FILTERS, REF MM 21-61-06-100-801, REPLACED THE TRIM AIR PRSOV IAW AMM 21-62-01-400-801. OPS TEST GOOD.