What was found
PASSENGER CABIN WAS EXCESSIVELY WARM IN FLIGHT WITH FWD CAB AND AFT CAB IN RELATIVELY NORMAL POSITIONS. TURNED FWD CAB AND AFT CAB CONTROLLERS WAY DOWN BUT PAX CABIN REMAINED WARM. REFERENCED QRH PROCEDURE AND TURNED TRIM AIR SWITCH OFF PAX CABIN TEMPERATURE GRADUALLY LOWERED TO AN ACCEPTABLE TEMPERATURE. GROUNDED - YES. BITE CKD BOTH ZONE TEMP CONT BOTH CK GOOD REF B737-900 AMM 21-61-00. NO FAULTS LOGGED. FOUND BOTH CABIN TEMP FILTERS CLOGGED CLEANED SAME SYS OPS NML GND VERIFICATION SUCCESSFUL.