What was found
CONTROL CABIN PACK TEMP CONTROLLER NOT OPERATING CORRECTLY. AT CRUISE ALT 340 AND 360, SLIGHT TEMP CHANGES CAUSE TEMP TO VARY FROM 2 DEGREES C TO 45 DEGREES C. CONSTANT ADJUSTING REQUIRED. DOESN'T APPEAR TO BE OPERATING NORMALLY. GROUNDED - YES. PERFORMED PACK ZONE TEMP CONTROLLER BITE, REF B737-800 FIM 21-62 TASK 801. NO FAULTS LOGGED. INSPECTED CONTROL CABIN ZONE TEMP SENSOR AND FAN, REF B737-800 FIM 21-61 TASK 861. FOUND CONTROL CABIN ZONE TEMP SENSOR AND SENSOR FAN COVERED WITH DIRT AND DUST. CLEANED SENSOR AND FAN. ACCOMPLISHED TEMP CONTROL INDICATION AND OPERATIONAL TEST FOR CONTROL CABIN PER B737-800 AMM 21-61-00-700-807-002. OPERATIONAL TEST NORMAL.